Re: [PATCH 13/14] scsi: add support for a blk-mq based I/O path.

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On Tue, Aug 19, 2014 at 3:51 AM, Kashyap Desai
<kashyap.desai@xxxxxxxxxxxxx> wrote:
>
> > -----Original Message-----
> > From: linux-scsi-owner@xxxxxxxxxxxxxxx [mailto:linux-scsi-
> > owner@xxxxxxxxxxxxxxx] On Behalf Of Christoph Hellwig
> > Sent: Friday, July 18, 2014 3:43 PM
> > To: James Bottomley; linux-scsi@xxxxxxxxxxxxxxx
> > Cc: Jens Axboe; Bart Van Assche; Mike Christie; Martin K. Petersen;
> Robert
> > Elliott; Webb Scales; linux-kernel@xxxxxxxxxxxxxxx
> > Subject: [PATCH 13/14] scsi: add support for a blk-mq based I/O path.
> >
> > This patch adds support for an alternate I/O path in the scsi midlayer
> which
> > uses the blk-mq infrastructure instead of the legacy request code.
> >
> > Use of blk-mq is fully transparent to drivers, although for now a host
> > template field is provided to opt out of blk-mq usage in case any
> unforseen
> > incompatibilities arise.
> >
> > In general replacing the legacy request code with blk-mq is a simple and
> > mostly mechanical transformation.  The biggest exception is the new code
> > that deals with the fact the I/O submissions in blk-mq must happen from
> > process context, which slightly complicates the I/O completion handler.
> > The second biggest differences is that blk-mq is build around the
> concept of
> > preallocated requests that also include driver specific data, which in
> SCSI
> > context means the scsi_cmnd structure.  This completely avoids dynamic
> > memory allocations for the fast path through I/O submission.
> >
> > Due the preallocated requests the MQ code path exclusively uses the
> host-
> > wide shared tag allocator instead of a per-LUN one.  This only affects
> drivers
> > actually using the block layer provided tag allocator instead of their
> own.
> > Unlike the old path blk-mq always provides a tag, although drivers don't
> have
> > to use it.
> >
> > For now the blk-mq path is disable by defauly and must be enabled using
> the
> > "use_blk_mq" module parameter.  Once the remaining work in the block
> > layer to make blk-mq more suitable for slow devices is complete I hope
> to
> > make it the default and eventually even remove the old code path.
> >
> > Based on the earlier scsi-mq prototype by Nicholas Bellinger.
> >
> > Thanks to Bart Van Assche and Robert Elliot for testing, benchmarking
> and
> > various sugestions and code contributions.
> >
> > Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> > Reviewed-by: Hannes Reinecke <hare@xxxxxxx>
> > Reviewed-by: Webb Scales <webbnh@xxxxxx>
> > Acked-by: Jens Axboe <axboe@xxxxxxxxx>
> > Tested-by: Bart Van Assche <bvanassche@xxxxxxx>
> > Tested-by: Robert Elliott <elliott@xxxxxx>
> > ---
> >  drivers/scsi/hosts.c      |  35 +++-
> >  drivers/scsi/scsi.c       |   5 +-
> >  drivers/scsi/scsi_lib.c   | 464
> > ++++++++++++++++++++++++++++++++++++++++------
> >  drivers/scsi/scsi_priv.h  |   3 +
> >  drivers/scsi/scsi_scan.c  |   5 +-
> >  drivers/scsi/scsi_sysfs.c |   2 +
> >  include/scsi/scsi_host.h  |  18 +-
> >  include/scsi/scsi_tcq.h   |  28 ++-
> >  8 files changed, 488 insertions(+), 72 deletions(-)
> >
> > diff --git a/drivers/scsi/hosts.c b/drivers/scsi/hosts.c index
> 0632eee..6de80e3
> > 100644
> > --- a/drivers/scsi/hosts.c
> > +++ b/drivers/scsi/hosts.c
> > @@ -213,9 +213,24 @@ int scsi_add_host_with_dma(struct Scsi_Host
> > *shost, struct device *dev,
> >               goto fail;
> >       }
> >
> > +     if (shost_use_blk_mq(shost)) {
> > +             error = scsi_mq_setup_tags(shost);
> > +             if (error)
> > +                     goto fail;
> > +     }
> > +
> > +     /*
> > +      * Note that we allocate the freelist even for the MQ case for
> now,
> > +      * as we need a command set aside for scsi_reset_provider.  Having
> > +      * the full host freelist and one command available for that is a
> > +      * little heavy-handed, but avoids introducing a special allocator
> > +      * just for this.  Eventually the structure of scsi_reset_provider
> > +      * will need a major overhaul.
> > +      */
> >       error = scsi_setup_command_freelist(shost);
> >       if (error)
> > -             goto fail;
> > +             goto out_destroy_tags;
> > +
> >
> >       if (!shost->shost_gendev.parent)
> >               shost->shost_gendev.parent = dev ? dev : &platform_bus;
> > @@ -226,7 +241,7 @@ int scsi_add_host_with_dma(struct Scsi_Host *shost,
> > struct device *dev,
> >
> >       error = device_add(&shost->shost_gendev);
> >       if (error)
> > -             goto out;
> > +             goto out_destroy_freelist;
> >
> >       pm_runtime_set_active(&shost->shost_gendev);
> >       pm_runtime_enable(&shost->shost_gendev);
> > @@ -279,8 +294,11 @@ int scsi_add_host_with_dma(struct Scsi_Host
> > *shost, struct device *dev,
> >       device_del(&shost->shost_dev);
> >   out_del_gendev:
> >       device_del(&shost->shost_gendev);
> > - out:
> > + out_destroy_freelist:
> >       scsi_destroy_command_freelist(shost);
> > + out_destroy_tags:
> > +     if (shost_use_blk_mq(shost))
> > +             scsi_mq_destroy_tags(shost);
> >   fail:
> >       return error;
> >  }
> > @@ -309,8 +327,13 @@ static void scsi_host_dev_release(struct device
> > *dev)
> >       }
> >
> >       scsi_destroy_command_freelist(shost);
> > -     if (shost->bqt)
> > -             blk_free_tags(shost->bqt);
> > +     if (shost_use_blk_mq(shost)) {
> > +             if (shost->tag_set.tags)
> > +                     scsi_mq_destroy_tags(shost);
> > +     } else {
> > +             if (shost->bqt)
> > +                     blk_free_tags(shost->bqt);
> > +     }
> >
> >       kfree(shost->shost_data);
> >
> > @@ -436,6 +459,8 @@ struct Scsi_Host *scsi_host_alloc(struct
> > scsi_host_template *sht, int privsize)
> >       else
> >               shost->dma_boundary = 0xffffffff;
> >
> > +     shost->use_blk_mq = scsi_use_blk_mq && !shost->hostt-
> > >disable_blk_mq;
> > +
> >       device_initialize(&shost->shost_gendev);
> >       dev_set_name(&shost->shost_gendev, "host%d", shost->host_no);
> >       shost->shost_gendev.bus = &scsi_bus_type; diff --git
> > a/drivers/scsi/scsi.c b/drivers/scsi/scsi.c index 3dde8a3..013709f
> 100644
> > --- a/drivers/scsi/scsi.c
> > +++ b/drivers/scsi/scsi.c
> > @@ -805,7 +805,7 @@ void scsi_adjust_queue_depth(struct scsi_device
> > *sdev, int tagged, int tags)
> >        * is more IO than the LLD's can_queue (so there are not enuogh
> >        * tags) request_fn's host queue ready check will handle it.
> >        */
> > -     if (!sdev->host->bqt) {
> > +     if (!shost_use_blk_mq(sdev->host) && !sdev->host->bqt) {
> >               if (blk_queue_tagged(sdev->request_queue) &&
> >                   blk_queue_resize_tags(sdev->request_queue, tags) != 0)
> >                       goto out;
> > @@ -1361,6 +1361,9 @@ MODULE_LICENSE("GPL");
> > module_param(scsi_logging_level, int, S_IRUGO|S_IWUSR);
> > MODULE_PARM_DESC(scsi_logging_level, "a bit mask of logging levels");
> >
> > +bool scsi_use_blk_mq = false;
> > +module_param_named(use_blk_mq, scsi_use_blk_mq, bool, S_IWUSR |
> > +S_IRUGO);
> > +
> >  static int __init init_scsi(void)
> >  {
> >       int error;
> > diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c index
> > bbd7a0a..9c44392 100644
> > --- a/drivers/scsi/scsi_lib.c
> > +++ b/drivers/scsi/scsi_lib.c
> > @@ -1,5 +1,6 @@
> >  /*
> > - *  scsi_lib.c Copyright (C) 1999 Eric Youngdale
> > + * Copyright (C) 1999 Eric Youngdale
> > + * Copyright (C) 2014 Christoph Hellwig
> >   *
> >   *  SCSI queueing library.
> >   *      Initial versions: Eric Youngdale (eric@xxxxxxxxxxx).
> > @@ -20,6 +21,7 @@
> >  #include <linux/delay.h>
> >  #include <linux/hardirq.h>
> >  #include <linux/scatterlist.h>
> > +#include <linux/blk-mq.h>
> >
> >  #include <scsi/scsi.h>
> >  #include <scsi/scsi_cmnd.h>
> > @@ -113,6 +115,16 @@ scsi_set_blocked(struct scsi_cmnd *cmd, int reason)
> >       }
> >  }
> >
> > +static void scsi_mq_requeue_cmd(struct scsi_cmnd *cmd) {
> > +     struct scsi_device *sdev = cmd->device;
> > +     struct request_queue *q = cmd->request->q;
> > +
> > +     blk_mq_requeue_request(cmd->request);
> > +     blk_mq_kick_requeue_list(q);
> > +     put_device(&sdev->sdev_gendev);
> > +}
> > +
> >  /**
> >   * __scsi_queue_insert - private queue insertion
> >   * @cmd: The SCSI command being requeued @@ -150,6 +162,10 @@ static
> > void __scsi_queue_insert(struct scsi_cmnd *cmd, int reason, int unbusy)
> >        * before blk_cleanup_queue() finishes.
> >        */
> >       cmd->result = 0;
> > +     if (q->mq_ops) {
> > +             scsi_mq_requeue_cmd(cmd);
> > +             return;
> > +     }
> >       spin_lock_irqsave(q->queue_lock, flags);
> >       blk_requeue_request(q, cmd->request);
> >       kblockd_schedule_work(&device->requeue_work);
> > @@ -308,6 +324,14 @@ void scsi_device_unbusy(struct scsi_device *sdev)
> >       atomic_dec(&sdev->device_busy);
> >  }
> >
> > +static void scsi_kick_queue(struct request_queue *q) {
> > +     if (q->mq_ops)
> > +             blk_mq_start_hw_queues(q);
> > +     else
> > +             blk_run_queue(q);
> > +}
> > +
> >  /*
> >   * Called for single_lun devices on IO completion. Clear
> starget_sdev_user,
> >   * and call blk_run_queue for all the scsi_devices on the target - @@
> -332,7
> > +356,7 @@ static void scsi_single_lun_run(struct scsi_device
> *current_sdev)
> >        * but in most cases, we will be first. Ideally, each LU on the
> >        * target would get some limited time or requests on the target.
> >        */
> > -     blk_run_queue(current_sdev->request_queue);
> > +     scsi_kick_queue(current_sdev->request_queue);
> >
> >       spin_lock_irqsave(shost->host_lock, flags);
> >       if (starget->starget_sdev_user)
> > @@ -345,7 +369,7 @@ static void scsi_single_lun_run(struct scsi_device
> > *current_sdev)
> >                       continue;
> >
> >               spin_unlock_irqrestore(shost->host_lock, flags);
> > -             blk_run_queue(sdev->request_queue);
> > +             scsi_kick_queue(sdev->request_queue);
> >               spin_lock_irqsave(shost->host_lock, flags);
> >
> >               scsi_device_put(sdev);
> > @@ -435,7 +459,7 @@ static void scsi_starved_list_run(struct Scsi_Host
> > *shost)
> >                       continue;
> >               spin_unlock_irqrestore(shost->host_lock, flags);
> >
> > -             blk_run_queue(slq);
> > +             scsi_kick_queue(slq);
> >               blk_put_queue(slq);
> >
> >               spin_lock_irqsave(shost->host_lock, flags); @@ -466,7
> > +490,10 @@ static void scsi_run_queue(struct request_queue *q)
> >       if (!list_empty(&sdev->host->starved_list))
> >               scsi_starved_list_run(sdev->host);
> >
> > -     blk_run_queue(q);
> > +     if (q->mq_ops)
> > +             blk_mq_start_stopped_hw_queues(q, false);
> > +     else
> > +             blk_run_queue(q);
> >  }
> >
> >  void scsi_requeue_run_queue(struct work_struct *work) @@ -564,25
> > +591,72 @@ static struct scatterlist *scsi_sg_alloc(unsigned int nents,
> gfp_t
> > gfp_mask)
> >       return mempool_alloc(sgp->pool, gfp_mask);  }
> >
> > -static void scsi_free_sgtable(struct scsi_data_buffer *sdb)
> > +static void scsi_free_sgtable(struct scsi_data_buffer *sdb, bool mq)
> >  {
> > -     __sg_free_table(&sdb->table, SCSI_MAX_SG_SEGMENTS, false,
> > scsi_sg_free);
> > +     if (mq && sdb->table.nents <= SCSI_MAX_SG_SEGMENTS)
> > +             return;
> > +     __sg_free_table(&sdb->table, SCSI_MAX_SG_SEGMENTS, mq,
> > scsi_sg_free);
> >  }
> >
> >  static int scsi_alloc_sgtable(struct scsi_data_buffer *sdb, int nents,
> > -                           gfp_t gfp_mask)
> > +                           gfp_t gfp_mask, bool mq)
> >  {
> > +     struct scatterlist *first_chunk = NULL;
> >       int ret;
> >
> >       BUG_ON(!nents);
> >
> > +     if (mq) {
> > +             if (nents <= SCSI_MAX_SG_SEGMENTS) {
> > +                     sdb->table.nents = nents;
> > +                     sg_init_table(sdb->table.sgl, sdb->table.nents);
> > +                     return 0;
> > +             }
> > +             first_chunk = sdb->table.sgl;
> > +     }
> > +
> >       ret = __sg_alloc_table(&sdb->table, nents,
> > SCSI_MAX_SG_SEGMENTS,
> > -                            NULL, gfp_mask, scsi_sg_alloc);
> > +                            first_chunk, gfp_mask, scsi_sg_alloc);
> >       if (unlikely(ret))
> > -             scsi_free_sgtable(sdb);
> > +             scsi_free_sgtable(sdb, mq);
> >       return ret;
> >  }
> >
> > +static void scsi_uninit_cmd(struct scsi_cmnd *cmd) {
> > +     if (cmd->request->cmd_type == REQ_TYPE_FS) {
> > +             struct scsi_driver *drv = scsi_cmd_to_driver(cmd);
> > +
> > +             if (drv->uninit_command)
> > +                     drv->uninit_command(cmd);
> > +     }
> > +}
> > +
> > +static void scsi_mq_free_sgtables(struct scsi_cmnd *cmd) {
> > +     if (cmd->sdb.table.nents)
> > +             scsi_free_sgtable(&cmd->sdb, true);
> > +     if (cmd->request->next_rq && cmd->request->next_rq->special)
> > +             scsi_free_sgtable(cmd->request->next_rq->special, true);
> > +     if (scsi_prot_sg_count(cmd))
> > +             scsi_free_sgtable(cmd->prot_sdb, true); }
> > +
> > +static void scsi_mq_uninit_cmd(struct scsi_cmnd *cmd) {
> > +     struct scsi_device *sdev = cmd->device;
> > +     unsigned long flags;
> > +
> > +     BUG_ON(list_empty(&cmd->list));
> > +
> > +     scsi_mq_free_sgtables(cmd);
> > +     scsi_uninit_cmd(cmd);
> > +
> > +     spin_lock_irqsave(&sdev->list_lock, flags);
> > +     list_del_init(&cmd->list);
> > +     spin_unlock_irqrestore(&sdev->list_lock, flags); }
> > +
> >  /*
> >   * Function:    scsi_release_buffers()
> >   *
> > @@ -602,19 +676,19 @@ static int scsi_alloc_sgtable(struct
> scsi_data_buffer
> > *sdb, int nents,  static void scsi_release_buffers(struct scsi_cmnd
> *cmd)  {
> >       if (cmd->sdb.table.nents)
> > -             scsi_free_sgtable(&cmd->sdb);
> > +             scsi_free_sgtable(&cmd->sdb, false);
> >
> >       memset(&cmd->sdb, 0, sizeof(cmd->sdb));
> >
> >       if (scsi_prot_sg_count(cmd))
> > -             scsi_free_sgtable(cmd->prot_sdb);
> > +             scsi_free_sgtable(cmd->prot_sdb, false);
> >  }
> >
> >  static void scsi_release_bidi_buffers(struct scsi_cmnd *cmd)  {
> >       struct scsi_data_buffer *bidi_sdb = cmd->request->next_rq-
> > >special;
> >
> > -     scsi_free_sgtable(bidi_sdb);
> > +     scsi_free_sgtable(bidi_sdb, false);
> >       kmem_cache_free(scsi_sdb_cache, bidi_sdb);
> >       cmd->request->next_rq->special = NULL;  } @@ -625,8 +699,6 @@
> > static bool scsi_end_request(struct request *req, int error,
> >       struct scsi_cmnd *cmd = req->special;
> >       struct scsi_device *sdev = cmd->device;
> >       struct request_queue *q = sdev->request_queue;
> > -     unsigned long flags;
> > -
> >
> >       if (blk_update_request(req, error, bytes))
> >               return true;
> > @@ -639,14 +711,38 @@ static bool scsi_end_request(struct request *req,
> > int error,
> >       if (blk_queue_add_random(q))
> >               add_disk_randomness(req->rq_disk);
> >
> > -     spin_lock_irqsave(q->queue_lock, flags);
> > -     blk_finish_request(req, error);
> > -     spin_unlock_irqrestore(q->queue_lock, flags);
> > +     if (req->mq_ctx) {
> > +             /*
> > +              * In the MQ case the command gets freed by
> > __blk_mq_end_io,
> > +              * so we have to do all cleanup that depends on it
> earlier.
> > +              *
> > +              * We also can't kick the queues from irq context, so we
> > +              * will have to defer it to a workqueue.
> > +              */
> > +             scsi_mq_uninit_cmd(cmd);
> > +
> > +             __blk_mq_end_io(req, error);
> > +
> > +             if (scsi_target(sdev)->single_lun ||
> > +                 !list_empty(&sdev->host->starved_list))
> > +                     kblockd_schedule_work(&sdev->requeue_work);
> > +             else
> > +                     blk_mq_start_stopped_hw_queues(q, true);
> > +
> > +             put_device(&sdev->sdev_gendev);
> > +     } else {
> > +             unsigned long flags;
> > +
> > +             spin_lock_irqsave(q->queue_lock, flags);
> > +             blk_finish_request(req, error);
> > +             spin_unlock_irqrestore(q->queue_lock, flags);
> > +
> > +             if (bidi_bytes)
> > +                     scsi_release_bidi_buffers(cmd);
> > +             scsi_release_buffers(cmd);
> > +             scsi_next_command(cmd);
> > +     }
> >
> > -     if (bidi_bytes)
> > -             scsi_release_bidi_buffers(cmd);
> > -     scsi_release_buffers(cmd);
> > -     scsi_next_command(cmd);
> >       return false;
> >  }
> >
> > @@ -953,8 +1049,14 @@ void scsi_io_completion(struct scsi_cmnd *cmd,
> > unsigned int good_bytes)
> >               /* Unprep the request and put it back at the head of the
> > queue.
> >                * A new command will be prepared and issued.
> >                */
> > -             scsi_release_buffers(cmd);
> > -             scsi_requeue_command(q, cmd);
> > +             if (q->mq_ops) {
> > +                     cmd->request->cmd_flags &= ~REQ_DONTPREP;
> > +                     scsi_mq_uninit_cmd(cmd);
> > +                     scsi_mq_requeue_cmd(cmd);
> > +             } else {
> > +                     scsi_release_buffers(cmd);
> > +                     scsi_requeue_command(q, cmd);
> > +             }
> >               break;
> >       case ACTION_RETRY:
> >               /* Retry the same command immediately */ @@ -976,9
> > +1078,8 @@ static int scsi_init_sgtable(struct request *req, struct
> > scsi_data_buffer *sdb,
> >        * If sg table allocation fails, requeue request later.
> >        */
> >       if (unlikely(scsi_alloc_sgtable(sdb, req->nr_phys_segments,
> > -                                     gfp_mask))) {
> > +                                     gfp_mask, req->mq_ctx != NULL)))
> >               return BLKPREP_DEFER;
> > -     }
> >
> >       /*
> >        * Next, walk the list, and fill in the addresses and sizes of @@
> -
> > 1006,6 +1107,7 @@ int scsi_init_io(struct scsi_cmnd *cmd, gfp_t
> gfp_mask)  {
> >       struct scsi_device *sdev = cmd->device;
> >       struct request *rq = cmd->request;
> > +     bool is_mq = (rq->mq_ctx != NULL);
> >       int error;
> >
> >       BUG_ON(!rq->nr_phys_segments);
> > @@ -1015,15 +1117,19 @@ int scsi_init_io(struct scsi_cmnd *cmd, gfp_t
> > gfp_mask)
> >               goto err_exit;
> >
> >       if (blk_bidi_rq(rq)) {
> > -             struct scsi_data_buffer *bidi_sdb = kmem_cache_zalloc(
> > -                     scsi_sdb_cache, GFP_ATOMIC);
> > -             if (!bidi_sdb) {
> > -                     error = BLKPREP_DEFER;
> > -                     goto err_exit;
> > +             if (!rq->q->mq_ops) {
> > +                     struct scsi_data_buffer *bidi_sdb =
> > +                             kmem_cache_zalloc(scsi_sdb_cache,
> > GFP_ATOMIC);
> > +                     if (!bidi_sdb) {
> > +                             error = BLKPREP_DEFER;
> > +                             goto err_exit;
> > +                     }
> > +
> > +                     rq->next_rq->special = bidi_sdb;
> >               }
> >
> > -             rq->next_rq->special = bidi_sdb;
> > -             error = scsi_init_sgtable(rq->next_rq, bidi_sdb,
> > GFP_ATOMIC);
> > +             error = scsi_init_sgtable(rq->next_rq,
> rq->next_rq->special,
> > +                                       GFP_ATOMIC);
> >               if (error)
> >                       goto err_exit;
> >       }
> > @@ -1035,7 +1141,7 @@ int scsi_init_io(struct scsi_cmnd *cmd, gfp_t
> > gfp_mask)
> >               BUG_ON(prot_sdb == NULL);
> >               ivecs = blk_rq_count_integrity_sg(rq->q, rq->bio);
> >
> > -             if (scsi_alloc_sgtable(prot_sdb, ivecs, gfp_mask)) {
> > +             if (scsi_alloc_sgtable(prot_sdb, ivecs, gfp_mask, is_mq))
> {
> >                       error = BLKPREP_DEFER;
> >                       goto err_exit;
> >               }
> > @@ -1049,13 +1155,16 @@ int scsi_init_io(struct scsi_cmnd *cmd, gfp_t
> > gfp_mask)
> >               cmd->prot_sdb->table.nents = count;
> >       }
> >
> > -     return BLKPREP_OK ;
> > -
> > +     return BLKPREP_OK;
> >  err_exit:
> > -     scsi_release_buffers(cmd);
> > -     cmd->request->special = NULL;
> > -     scsi_put_command(cmd);
> > -     put_device(&sdev->sdev_gendev);
> > +     if (is_mq) {
> > +             scsi_mq_free_sgtables(cmd);
> > +     } else {
> > +             scsi_release_buffers(cmd);
> > +             cmd->request->special = NULL;
> > +             scsi_put_command(cmd);
> > +             put_device(&sdev->sdev_gendev);
> > +     }
> >       return error;
> >  }
> >  EXPORT_SYMBOL(scsi_init_io);
> > @@ -1266,13 +1375,7 @@ out:
> >
> >  static void scsi_unprep_fn(struct request_queue *q, struct request
> *req)  {
> > -     if (req->cmd_type == REQ_TYPE_FS) {
> > -             struct scsi_cmnd *cmd = req->special;
> > -             struct scsi_driver *drv = scsi_cmd_to_driver(cmd);
> > -
> > -             if (drv->uninit_command)
> > -                     drv->uninit_command(cmd);
> > -     }
> > +     scsi_uninit_cmd(req->special);
> >  }
> >
> >  /*
> > @@ -1295,7 +1398,11 @@ static inline int scsi_dev_queue_ready(struct
> > request_queue *q,
> >                * unblock after device_blocked iterates to zero
> >                */
> >               if (atomic_dec_return(&sdev->device_blocked) > 0) {
> > -                     blk_delay_queue(q, SCSI_QUEUE_DELAY);
> > +                     /*
> > +                      * For the MQ case we take care of this in the
> caller.
> > +                      */
> > +                     if (!q->mq_ops)
> > +                             blk_delay_queue(q, SCSI_QUEUE_DELAY);
> >                       goto out_dec;
> >               }
> >               SCSI_LOG_MLQUEUE(3, sdev_printk(KERN_INFO, sdev, @@
> > -1671,6 +1778,180 @@ out_delay:
> >               blk_delay_queue(q, SCSI_QUEUE_DELAY);  }
> >
> > +static inline int prep_to_mq(int ret)
> > +{
> > +     switch (ret) {
> > +     case BLKPREP_OK:
> > +             return 0;
> > +     case BLKPREP_DEFER:
> > +             return BLK_MQ_RQ_QUEUE_BUSY;
> > +     default:
> > +             return BLK_MQ_RQ_QUEUE_ERROR;
> > +     }
> > +}
> > +
> > +static int scsi_mq_prep_fn(struct request *req) {
> > +     struct scsi_cmnd *cmd = blk_mq_rq_to_pdu(req);
> > +     struct scsi_device *sdev = req->q->queuedata;
> > +     struct Scsi_Host *shost = sdev->host;
> > +     unsigned char *sense_buf = cmd->sense_buffer;
> > +     struct scatterlist *sg;
> > +
> > +     memset(cmd, 0, sizeof(struct scsi_cmnd));
> > +
> > +     req->special = cmd;
> > +
> > +     cmd->request = req;
> > +     cmd->device = sdev;
> > +     cmd->sense_buffer = sense_buf;
> > +
> > +     cmd->tag = req->tag;
> > +
> > +     req->cmd = req->__cmd;
> > +     cmd->cmnd = req->cmd;
> > +     cmd->prot_op = SCSI_PROT_NORMAL;
> > +
> > +     INIT_LIST_HEAD(&cmd->list);
> > +     INIT_DELAYED_WORK(&cmd->abort_work,
> > scmd_eh_abort_handler);
> > +     cmd->jiffies_at_alloc = jiffies;
> > +
> > +     /*
> > +      * XXX: cmd_list lookups are only used by two drivers, try to get
> > +      * rid of this list in common code.
> > +      */
> > +     spin_lock_irq(&sdev->list_lock);
> > +     list_add_tail(&cmd->list, &sdev->cmd_list);
> > +     spin_unlock_irq(&sdev->list_lock);
>
> Hi Chris,
>
> I am using scsi.mq.4 branch and doing profiling to find out possible
> improvement in low level driver to get benefit of SCSI.MQ.  I am using
> LSI/Avago 12G MegaRaid Invader and total 12 SSDs (of 12Gpb/s).
> I have done some changes in "megaraid_sas" driver to gain from scsi.mq
> interface. I will send the list of changes some time later to get early
> feedback..
>
> I used this thread to reply as I found relevant patch to explain you
> better.
>
> Here are few data points - ( I used 4K Rand READ  FIO-libaio load on Two
> socket Super micro server)
>
> If I use "null_blk" driver, I was able to get 1800K IOPs on my setup
> When I used "megaraid_sas" driver in loop back mode (FAKE READ/WRITE), I
> see below numbers.
> Keep the worker on Node-0, 1800K IOPs (similar to null_blk), but when I
> spread workers on Node-0 and Node-1, I see ~700K IOPS.
>
> Above experiment hint me that there may be some difference in SCSI.MQ
> compare to BLK-MQ.
>
> My original problem was - "12 Drives R0 cannot scale beyond 750K IOPS, but
> it goes upto 1200K IOPS if I keep workers on Node-0 using cpus_allowed
> parameter of fio"
>
> Lock stats data  - Below data is for work load where I was not able to
> scale beyond 750K IOPS..
>
>
> --------------------------------------------------------------------------
> ------
>                               class name    con-bounces    contentions
> waittime-min   waittime-max waittime-total   waittime-avg    acq-bounces
> acquisitions   holdtime-min   holdtime-max holdtime-total   holdtime-avg
> --------------------------------------------------------------------------
> --------------------------------------------------------------------------
> -------------------------------------------------------------------------
>
>               &(&sdev->list_lock)->rlock:       2307248        2308395
> 0.07         158.89    10435357.44           4.52        3849400
> 3958002           0.04          26.02     1123671.56           0.28
>               --------------------------
>               &(&sdev->list_lock)->rlock        1105029
> [<ffffffff814ac980>] scsi_queue_rq+0x560/0x750
>               &(&sdev->list_lock)->rlock        1203366
> [<ffffffff814abc97>] scsi_mq_uninit_cmd+0x47/0xb0
>               --------------------------
>               &(&sdev->list_lock)->rlock        1176271
> [<ffffffff814abc97>] scsi_mq_uninit_cmd+0x47/0xb0
>               &(&sdev->list_lock)->rlock        1132124
> [<ffffffff814ac980>] scsi_queue_rq+0x560/0x750
>
>
>
> I read  this comment and find that very few drivers are using this
> cmd_list.  I think if we remove this cmd_list, performance will scale as I
> am seeing major contention in this lock.
> Just thought to ping you to see if this is known limitation for now or any
> plan to change this lock in near future ?

Additional info -

I tried after removing spinlock + list_add/del from scsi_mq_uninit()
and scsi_queue_rq(), IOPs are able to scale now upto 1100K (earlier
only 700K IOPS) which is almost similar to IO load running on single
Numa Node.


>
>
> ~ Kashyap
>
> > +
> > +     sg = (void *)cmd + sizeof(struct scsi_cmnd) + shost->hostt-
> > >cmd_size;
> > +     cmd->sdb.table.sgl = sg;
> > +
> > +     if (scsi_host_get_prot(shost)) {
> > +             cmd->prot_sdb = (void *)sg +
> > +                     shost->sg_tablesize * sizeof(struct scatterlist);
> > +             memset(cmd->prot_sdb, 0, sizeof(struct scsi_data_buffer));
> > +
> > +             cmd->prot_sdb->table.sgl =
> > +                     (struct scatterlist *)(cmd->prot_sdb + 1);
> > +     }
> > +
> > +     if (blk_bidi_rq(req)) {
> > +             struct request *next_rq = req->next_rq;
> > +             struct scsi_data_buffer *bidi_sdb =
> > blk_mq_rq_to_pdu(next_rq);
> > +
> > +             memset(bidi_sdb, 0, sizeof(struct scsi_data_buffer));
> > +             bidi_sdb->table.sgl =
> > +                     (struct scatterlist *)(bidi_sdb + 1);
> > +
> > +             next_rq->special = bidi_sdb;
> > +     }
> > +
> > +     return scsi_setup_cmnd(sdev, req);
> > +}
> > +
> > +static void scsi_mq_done(struct scsi_cmnd *cmd) {
> > +     trace_scsi_dispatch_cmd_done(cmd);
> > +     blk_mq_complete_request(cmd->request);
> > +}
> > +
> > +static int scsi_queue_rq(struct blk_mq_hw_ctx *hctx, struct request
> > +*req) {
> > +     struct request_queue *q = req->q;
> > +     struct scsi_device *sdev = q->queuedata;
> > +     struct Scsi_Host *shost = sdev->host;
> > +     struct scsi_cmnd *cmd = blk_mq_rq_to_pdu(req);
> > +     int ret;
> > +     int reason;
> > +
> > +     ret = prep_to_mq(scsi_prep_state_check(sdev, req));
> > +     if (ret)
> > +             goto out;
> > +
> > +     ret = BLK_MQ_RQ_QUEUE_BUSY;
> > +     if (!get_device(&sdev->sdev_gendev))
> > +             goto out;
> > +
> > +     if (!scsi_dev_queue_ready(q, sdev))
> > +             goto out_put_device;
> > +     if (!scsi_target_queue_ready(shost, sdev))
> > +             goto out_dec_device_busy;
> > +     if (!scsi_host_queue_ready(q, shost, sdev))
> > +             goto out_dec_target_busy;
> > +
> > +     if (!(req->cmd_flags & REQ_DONTPREP)) {
> > +             ret = prep_to_mq(scsi_mq_prep_fn(req));
> > +             if (ret)
> > +                     goto out_dec_host_busy;
> > +             req->cmd_flags |= REQ_DONTPREP;
> > +     }
> > +
> > +     scsi_init_cmd_errh(cmd);
> > +     cmd->scsi_done = scsi_mq_done;
> > +
> > +     reason = scsi_dispatch_cmd(cmd);
> > +     if (reason) {
> > +             scsi_set_blocked(cmd, reason);
> > +             ret = BLK_MQ_RQ_QUEUE_BUSY;
> > +             goto out_dec_host_busy;
> > +     }
> > +
> > +     return BLK_MQ_RQ_QUEUE_OK;
> > +
> > +out_dec_host_busy:
> > +     atomic_dec(&shost->host_busy);
> > +out_dec_target_busy:
> > +     if (scsi_target(sdev)->can_queue > 0)
> > +             atomic_dec(&scsi_target(sdev)->target_busy);
> > +out_dec_device_busy:
> > +     atomic_dec(&sdev->device_busy);
> > +out_put_device:
> > +     put_device(&sdev->sdev_gendev);
> > +out:
> > +     switch (ret) {
> > +     case BLK_MQ_RQ_QUEUE_BUSY:
> > +             blk_mq_stop_hw_queue(hctx);
> > +             if (atomic_read(&sdev->device_busy) == 0 &&
> > +                 !scsi_device_blocked(sdev))
> > +                     blk_mq_delay_queue(hctx, SCSI_QUEUE_DELAY);
> > +             break;
> > +     case BLK_MQ_RQ_QUEUE_ERROR:
> > +             /*
> > +              * Make sure to release all allocated ressources when
> > +              * we hit an error, as we will never see this command
> > +              * again.
> > +              */
> > +             if (req->cmd_flags & REQ_DONTPREP)
> > +                     scsi_mq_uninit_cmd(cmd);
> > +             break;
> > +     default:
> > +             break;
> > +     }
> > +     return ret;
> > +}
> > +
> > +static int scsi_init_request(void *data, struct request *rq,
> > +             unsigned int hctx_idx, unsigned int request_idx,
> > +             unsigned int numa_node)
> > +{
> > +     struct scsi_cmnd *cmd = blk_mq_rq_to_pdu(rq);
> > +
> > +     cmd->sense_buffer = kzalloc_node(SCSI_SENSE_BUFFERSIZE,
> > GFP_KERNEL,
> > +                     numa_node);
> > +     if (!cmd->sense_buffer)
> > +             return -ENOMEM;
> > +     return 0;
> > +}
> > +
> > +static void scsi_exit_request(void *data, struct request *rq,
> > +             unsigned int hctx_idx, unsigned int request_idx) {
> > +     struct scsi_cmnd *cmd = blk_mq_rq_to_pdu(rq);
> > +
> > +     kfree(cmd->sense_buffer);
> > +}
> > +
> >  static u64 scsi_calculate_bounce_limit(struct Scsi_Host *shost)  {
> >       struct device *host_dev;
> > @@ -1692,16 +1973,10 @@ static u64 scsi_calculate_bounce_limit(struct
> > Scsi_Host *shost)
> >       return bounce_limit;
> >  }
> >
> > -struct request_queue *__scsi_alloc_queue(struct Scsi_Host *shost,
> > -                                      request_fn_proc *request_fn)
> > +static void __scsi_init_queue(struct Scsi_Host *shost, struct
> > +request_queue *q)
> >  {
> > -     struct request_queue *q;
> >       struct device *dev = shost->dma_dev;
> >
> > -     q = blk_init_queue(request_fn, NULL);
> > -     if (!q)
> > -             return NULL;
> > -
> >       /*
> >        * this limit is imposed by hardware restrictions
> >        */
> > @@ -1732,7 +2007,17 @@ struct request_queue *__scsi_alloc_queue(struct
> > Scsi_Host *shost,
> >        * blk_queue_update_dma_alignment() later.
> >        */
> >       blk_queue_dma_alignment(q, 0x03);
> > +}
> >
> > +struct request_queue *__scsi_alloc_queue(struct Scsi_Host *shost,
> > +                                      request_fn_proc *request_fn)
> > +{
> > +     struct request_queue *q;
> > +
> > +     q = blk_init_queue(request_fn, NULL);
> > +     if (!q)
> > +             return NULL;
> > +     __scsi_init_queue(shost, q);
> >       return q;
> >  }
> >  EXPORT_SYMBOL(__scsi_alloc_queue);
> > @@ -1753,6 +2038,55 @@ struct request_queue *scsi_alloc_queue(struct
> > scsi_device *sdev)
> >       return q;
> >  }
> >
> > +static struct blk_mq_ops scsi_mq_ops = {
> > +     .map_queue      = blk_mq_map_queue,
> > +     .queue_rq       = scsi_queue_rq,
> > +     .complete       = scsi_softirq_done,
> > +     .timeout        = scsi_times_out,
> > +     .init_request   = scsi_init_request,
> > +     .exit_request   = scsi_exit_request,
> > +};
> > +
> > +struct request_queue *scsi_mq_alloc_queue(struct scsi_device *sdev) {
> > +     sdev->request_queue = blk_mq_init_queue(&sdev->host-
> > >tag_set);
> > +     if (IS_ERR(sdev->request_queue))
> > +             return NULL;
> > +
> > +     sdev->request_queue->queuedata = sdev;
> > +     __scsi_init_queue(sdev->host, sdev->request_queue);
> > +     return sdev->request_queue;
> > +}
> > +
> > +int scsi_mq_setup_tags(struct Scsi_Host *shost) {
> > +     unsigned int cmd_size, sgl_size, tbl_size;
> > +
> > +     tbl_size = shost->sg_tablesize;
> > +     if (tbl_size > SCSI_MAX_SG_SEGMENTS)
> > +             tbl_size = SCSI_MAX_SG_SEGMENTS;
> > +     sgl_size = tbl_size * sizeof(struct scatterlist);
> > +     cmd_size = sizeof(struct scsi_cmnd) + shost->hostt->cmd_size +
> > sgl_size;
> > +     if (scsi_host_get_prot(shost))
> > +             cmd_size += sizeof(struct scsi_data_buffer) + sgl_size;
> > +
> > +     memset(&shost->tag_set, 0, sizeof(shost->tag_set));
> > +     shost->tag_set.ops = &scsi_mq_ops;
> > +     shost->tag_set.nr_hw_queues = 1;
> > +     shost->tag_set.queue_depth = shost->can_queue;
> > +     shost->tag_set.cmd_size = cmd_size;
> > +     shost->tag_set.numa_node = NUMA_NO_NODE;
> > +     shost->tag_set.flags = BLK_MQ_F_SHOULD_MERGE |
> > BLK_MQ_F_SG_MERGE;
> > +     shost->tag_set.driver_data = shost;
> > +
> > +     return blk_mq_alloc_tag_set(&shost->tag_set);
> > +}
> > +
> > +void scsi_mq_destroy_tags(struct Scsi_Host *shost) {
> > +     blk_mq_free_tag_set(&shost->tag_set);
> > +}
> > +
> >  /*
> >   * Function:    scsi_block_requests()
> >   *
> > @@ -2498,9 +2832,13 @@ scsi_internal_device_block(struct scsi_device
> > *sdev)
> >        * block layer from calling the midlayer with this device's
> >        * request queue.
> >        */
> > -     spin_lock_irqsave(q->queue_lock, flags);
> > -     blk_stop_queue(q);
> > -     spin_unlock_irqrestore(q->queue_lock, flags);
> > +     if (q->mq_ops) {
> > +             blk_mq_stop_hw_queues(q);
> > +     } else {
> > +             spin_lock_irqsave(q->queue_lock, flags);
> > +             blk_stop_queue(q);
> > +             spin_unlock_irqrestore(q->queue_lock, flags);
> > +     }
> >
> >       return 0;
> >  }
> > @@ -2546,9 +2884,13 @@ scsi_internal_device_unblock(struct scsi_device
> > *sdev,
> >                sdev->sdev_state != SDEV_OFFLINE)
> >               return -EINVAL;
> >
> > -     spin_lock_irqsave(q->queue_lock, flags);
> > -     blk_start_queue(q);
> > -     spin_unlock_irqrestore(q->queue_lock, flags);
> > +     if (q->mq_ops) {
> > +             blk_mq_start_stopped_hw_queues(q, false);
> > +     } else {
> > +             spin_lock_irqsave(q->queue_lock, flags);
> > +             blk_start_queue(q);
> > +             spin_unlock_irqrestore(q->queue_lock, flags);
> > +     }
> >
> >       return 0;
> >  }
> > diff --git a/drivers/scsi/scsi_priv.h b/drivers/scsi/scsi_priv.h index
> > a45d1c2..12b8e1b 100644
> > --- a/drivers/scsi/scsi_priv.h
> > +++ b/drivers/scsi/scsi_priv.h
> > @@ -88,6 +88,9 @@ extern void scsi_next_command(struct scsi_cmnd
> > *cmd);  extern void scsi_io_completion(struct scsi_cmnd *, unsigned
> int);
> > extern void scsi_run_host_queues(struct Scsi_Host *shost);  extern
> struct
> > request_queue *scsi_alloc_queue(struct scsi_device *sdev);
> > +extern struct request_queue *scsi_mq_alloc_queue(struct scsi_device
> > +*sdev); extern int scsi_mq_setup_tags(struct Scsi_Host *shost); extern
> > +void scsi_mq_destroy_tags(struct Scsi_Host *shost);
> >  extern int scsi_init_queue(void);
> >  extern void scsi_exit_queue(void);
> >  struct request_queue;
> > diff --git a/drivers/scsi/scsi_scan.c b/drivers/scsi/scsi_scan.c index
> > 4a6e4ba..b91cfaf 100644
> > --- a/drivers/scsi/scsi_scan.c
> > +++ b/drivers/scsi/scsi_scan.c
> > @@ -273,7 +273,10 @@ static struct scsi_device *scsi_alloc_sdev(struct
> > scsi_target *starget,
> >        */
> >       sdev->borken = 1;
> >
> > -     sdev->request_queue = scsi_alloc_queue(sdev);
> > +     if (shost_use_blk_mq(shost))
> > +             sdev->request_queue = scsi_mq_alloc_queue(sdev);
> > +     else
> > +             sdev->request_queue = scsi_alloc_queue(sdev);
> >       if (!sdev->request_queue) {
> >               /* release fn is set up in scsi_sysfs_device_initialise,
> so
> >                * have to free and put manually here */ diff --git
> > a/drivers/scsi/scsi_sysfs.c b/drivers/scsi/scsi_sysfs.c index
> deef063..6c9227f
> > 100644
> > --- a/drivers/scsi/scsi_sysfs.c
> > +++ b/drivers/scsi/scsi_sysfs.c
> > @@ -333,6 +333,7 @@ store_shost_eh_deadline(struct device *dev, struct
> > device_attribute *attr,
> >
> >  static DEVICE_ATTR(eh_deadline, S_IRUGO | S_IWUSR,
> > show_shost_eh_deadline, store_shost_eh_deadline);
> >
> > +shost_rd_attr(use_blk_mq, "%d\n");
> >  shost_rd_attr(unique_id, "%u\n");
> >  shost_rd_attr(cmd_per_lun, "%hd\n");
> >  shost_rd_attr(can_queue, "%hd\n");
> > @@ -352,6 +353,7 @@ show_host_busy(struct device *dev, struct
> > device_attribute *attr, char *buf)  static DEVICE_ATTR(host_busy,
> S_IRUGO,
> > show_host_busy, NULL);
> >
> >  static struct attribute *scsi_sysfs_shost_attrs[] = {
> > +     &dev_attr_use_blk_mq.attr,
> >       &dev_attr_unique_id.attr,
> >       &dev_attr_host_busy.attr,
> >       &dev_attr_cmd_per_lun.attr,
> > diff --git a/include/scsi/scsi_host.h b/include/scsi/scsi_host.h index
> > 5e8ebc1..ba20347 100644
> > --- a/include/scsi/scsi_host.h
> > +++ b/include/scsi/scsi_host.h
> > @@ -7,6 +7,7 @@
> >  #include <linux/workqueue.h>
> >  #include <linux/mutex.h>
> >  #include <linux/seq_file.h>
> > +#include <linux/blk-mq.h>
> >  #include <scsi/scsi.h>
> >
> >  struct request_queue;
> > @@ -510,6 +511,9 @@ struct scsi_host_template {
> >        */
> >       unsigned int cmd_size;
> >       struct scsi_host_cmd_pool *cmd_pool;
> > +
> > +     /* temporary flag to disable blk-mq I/O path */
> > +     bool disable_blk_mq;
> >  };
> >
> >  /*
> > @@ -580,7 +584,10 @@ struct Scsi_Host {
> >        * Area to keep a shared tag map (if needed, will be
> >        * NULL if not).
> >        */
> > -     struct blk_queue_tag    *bqt;
> > +     union {
> > +             struct blk_queue_tag    *bqt;
> > +             struct blk_mq_tag_set   tag_set;
> > +     };
> >
> >       atomic_t host_busy;                /* commands actually active on
> low-
> > level */
> >       atomic_t host_blocked;
> > @@ -672,6 +679,8 @@ struct Scsi_Host {
> >       /* The controller does not support WRITE SAME */
> >       unsigned no_write_same:1;
> >
> > +     unsigned use_blk_mq:1;
> > +
> >       /*
> >        * Optional work queue to be utilized by the transport
> >        */
> > @@ -772,6 +781,13 @@ static inline int scsi_host_in_recovery(struct
> > Scsi_Host *shost)
> >               shost->tmf_in_progress;
> >  }
> >
> > +extern bool scsi_use_blk_mq;
> > +
> > +static inline bool shost_use_blk_mq(struct Scsi_Host *shost) {
> > +     return shost->use_blk_mq;
> > +}
> > +
> >  extern int scsi_queue_work(struct Scsi_Host *, struct work_struct *);
> > extern void scsi_flush_work(struct Scsi_Host *);
> >
> > diff --git a/include/scsi/scsi_tcq.h b/include/scsi/scsi_tcq.h index
> > 81dd12e..cdcc90b 100644
> > --- a/include/scsi/scsi_tcq.h
> > +++ b/include/scsi/scsi_tcq.h
> > @@ -67,7 +67,8 @@ static inline void scsi_activate_tcq(struct
> scsi_device
> > *sdev, int depth)
> >       if (!sdev->tagged_supported)
> >               return;
> >
> > -     if (!blk_queue_tagged(sdev->request_queue))
> > +     if (!shost_use_blk_mq(sdev->host) &&
> > +         blk_queue_tagged(sdev->request_queue))
> >               blk_queue_init_tags(sdev->request_queue, depth,
> >                                   sdev->host->bqt);
> >
> > @@ -80,7 +81,8 @@ static inline void scsi_activate_tcq(struct
> scsi_device
> > *sdev, int depth)
> >   **/
> >  static inline void scsi_deactivate_tcq(struct scsi_device *sdev, int
> depth)  {
> > -     if (blk_queue_tagged(sdev->request_queue))
> > +     if (!shost_use_blk_mq(sdev->host) &&
> > +         blk_queue_tagged(sdev->request_queue))
> >               blk_queue_free_tags(sdev->request_queue);
> >       scsi_adjust_queue_depth(sdev, 0, depth);  } @@ -108,6 +110,15 @@
> > static inline int scsi_populate_tag_msg(struct scsi_cmnd *cmd, char
> *msg)
> >       return 0;
> >  }
> >
> > +static inline struct scsi_cmnd *scsi_mq_find_tag(struct Scsi_Host
> *shost,
> > +             unsigned int hw_ctx, int tag)
> > +{
> > +     struct request *req;
> > +
> > +     req = blk_mq_tag_to_rq(shost->tag_set.tags[hw_ctx], tag);
> > +     return req ? (struct scsi_cmnd *)req->special : NULL; }
> > +
> >  /**
> >   * scsi_find_tag - find a tagged command by device
> >   * @SDpnt:   pointer to the ScSI device
> > @@ -118,10 +129,12 @@ static inline int scsi_populate_tag_msg(struct
> > scsi_cmnd *cmd, char *msg)
> >   **/
> >  static inline struct scsi_cmnd *scsi_find_tag(struct scsi_device *sdev,
> int tag)
> > {
> > -
> >          struct request *req;
> >
> >          if (tag != SCSI_NO_TAG) {
> > +             if (shost_use_blk_mq(sdev->host))
> > +                     return scsi_mq_find_tag(sdev->host, 0, tag);
> > +
> >               req = blk_queue_find_tag(sdev->request_queue, tag);
> >               return req ? (struct scsi_cmnd *)req->special : NULL;
> >       }
> > @@ -130,6 +143,7 @@ static inline struct scsi_cmnd *scsi_find_tag(struct
> > scsi_device *sdev, int tag)
> >       return sdev->current_cmnd;
> >  }
> >
> > +
> >  /**
> >   * scsi_init_shared_tag_map - create a shared tag map
> >   * @shost:   the host to share the tag map among all devices
> > @@ -138,6 +152,12 @@ static inline struct scsi_cmnd
> *scsi_find_tag(struct
> > scsi_device *sdev, int tag)  static inline int
> scsi_init_shared_tag_map(struct
> > Scsi_Host *shost, int depth)  {
> >       /*
> > +      * We always have a shared tag map around when using blk-mq.
> > +      */
> > +     if (shost_use_blk_mq(shost))
> > +             return 0;
> > +
> > +     /*
> >        * If the shared tag map isn't already initialized, do it now.
> >        * This saves callers from having to check ->bqt when setting up
> >        * devices on the shared host (for libata) @@ -165,6 +185,8 @@
> static
> > inline struct scsi_cmnd *scsi_host_find_tag(struct Scsi_Host *shost,
> >       struct request *req;
> >
> >       if (tag != SCSI_NO_TAG) {
> > +             if (shost_use_blk_mq(shost))
> > +                     return scsi_mq_find_tag(shost, 0, tag);
> >               req = blk_map_queue_find_tag(shost->bqt, tag);
> >               return req ? (struct scsi_cmnd *)req->special : NULL;
> >       }
> > --
> > 1.9.1
> >
> > --
> > To unsubscribe from this list: send the line "unsubscribe linux-scsi" in
> the
> > body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at
> > http://vger.kernel.org/majordomo-info.html




-- 
Device Driver Developer @ Avagotech
Kashyap D. Desai
Note - my new email address
kashyap.desai@xxxxxxxxxxxxx
--
To unsubscribe from this list: send the line "unsubscribe linux-scsi" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html




[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
[Index of Archives]     [SCSI Target Devel]     [Linux SCSI Target Infrastructure]     [Kernel Newbies]     [IDE]     [Security]     [Git]     [Netfilter]     [Bugtraq]     [Yosemite News]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux RAID]     [Linux ATA RAID]     [Linux IIO]     [Samba]     [Device Mapper]
  Powered by Linux