On Tue, Jan 15 2008 at 11:23 +0200, FUJITA Tomonori <fujita.tomonori@xxxxxxxxxxxxx> wrote: > This is the second version of > > http://marc.info/?l=linux-scsi&m=119933628210006&w=2 > > I gave up once, but I found that the performance loss is negligible > (within 1%) by using kmem_cache_alloc instead of mempool. > > I use scsi_debug with fake_rw=1 and disktest (DIO reads with 8 > threads) again: > > scsi-misc (slub) | 486.9 MB/s IOPS 124652.9/s > dynamic sense buf (slub) | 483.2 MB/s IOPS 123704.1/s > > scsi-misc (slab) | 467.0 MB/s IOPS 119544.3/s > dynamic sense buf (slab) | 468.7 MB/s IOPS 119986.0/s > > The results are the averages of three runs with a server using two > dual-core 1.60 GHz Xeon processors with DDR2 memory. > > > I doubt think that someone will complain about the performance > regression due to this patch. In addition, unlike scsi_debug, the real > LLDs allocate the own data structure per scsi_cmnd so the performance > differences would be smaller (and with the real hard disk overheads). > > Here's the full results: > > http://www.kernel.org/pub/linux/kernel/people/tomo/sense/results.txt > TOMO Hi. This is grate news. Thanks I like what you did here. and it's good to know. Why should a mempool be so slow ;) I have a small concern of a leak, please see below, but otherwise this is grate. > > = > From: FUJITA Tomonori <fujita.tomonori@xxxxxxxxxxxxx> > Subject: [PATCH] use dynamically allocated sense buffer > > This removes static array sense_buffer in scsi_cmnd and uses > dynamically allocated sense_buffer (with GFP_DMA). > > The reason for doing this is that some architectures need cacheline > aligned buffer for DMA: > > http://lkml.org/lkml/2007/11/19/2 > > The problems are that scsi_eh_prep_cmnd puts scsi_cmnd::sense_buffer > to sglist and some LLDs directly DMA to scsi_cmnd::sense_buffer. It's > necessary to DMA to scsi_cmnd::sense_buffer safely. This patch solves > these issues. > > __scsi_get_command allocates sense_buffer via kmem_cache_alloc and > attaches it to a scsi_cmnd so everything just work as before. > > A scsi_host reserves one sense buffer for the backup command > (shost->backup_sense_buffer). > > > Signed-off-by: FUJITA Tomonori <fujita.tomonori@xxxxxxxxxxxxx> > --- > drivers/scsi/hosts.c | 10 ++++++- > drivers/scsi/scsi.c | 67 ++++++++++++++++++++++++++++++++++++++++++++- > drivers/scsi/scsi_priv.h | 2 + > include/scsi/scsi_cmnd.h | 2 +- > include/scsi/scsi_host.h | 3 ++ > 5 files changed, 80 insertions(+), 4 deletions(-) > > diff --git a/drivers/scsi/hosts.c b/drivers/scsi/hosts.c > index 9a10b43..35c5f0e 100644 > --- a/drivers/scsi/hosts.c > +++ b/drivers/scsi/hosts.c > @@ -205,10 +205,14 @@ int scsi_add_host(struct Scsi_Host *shost, struct device *dev) > if (!shost->shost_gendev.parent) > shost->shost_gendev.parent = dev ? dev : &platform_bus; > > - error = device_add(&shost->shost_gendev); > + error = scsi_setup_command_sense_buffer(shost); > if (error) > goto out; > > + error = device_add(&shost->shost_gendev); > + if (error) > + goto destroy_pool; > + > scsi_host_set_state(shost, SHOST_RUNNING); > get_device(shost->shost_gendev.parent); > > @@ -248,6 +252,8 @@ int scsi_add_host(struct Scsi_Host *shost, struct device *dev) > class_device_del(&shost->shost_classdev); > out_del_gendev: > device_del(&shost->shost_gendev); > + destroy_pool: > + scsi_destroy_command_sense_buffer(shost); > out: > return error; > } > @@ -267,6 +273,8 @@ static void scsi_host_dev_release(struct device *dev) > scsi_free_queue(shost->uspace_req_q); > } > > + scsi_destroy_command_sense_buffer(shost); > + > scsi_destroy_command_freelist(shost); > if (shost->bqt) > blk_free_tags(shost->bqt); > diff --git a/drivers/scsi/scsi.c b/drivers/scsi/scsi.c > index 54ff611..d153da3 100644 > --- a/drivers/scsi/scsi.c > +++ b/drivers/scsi/scsi.c > @@ -161,6 +161,9 @@ static struct scsi_host_cmd_pool scsi_cmd_dma_pool = { > > static DEFINE_MUTEX(host_cmd_pool_mutex); > > +static struct kmem_cache *sense_buffer_slab; > +static int sense_buffer_slab_users; > + > /** > * __scsi_get_command - Allocate a struct scsi_cmnd > * @shost: host to transmit command > @@ -186,6 +189,22 @@ struct scsi_cmnd *__scsi_get_command(struct Scsi_Host *shost, gfp_t gfp_mask) > list_del_init(&cmd->list); > } > spin_unlock_irqrestore(&shost->free_list_lock, flags); > + > + if (cmd) { > + memset(cmd, 0, sizeof(*cmd)); > + cmd->sense_buffer = shost->backup_sense_buffer; [1] If command was put on free_list in __put_command(), then this here will leak the sense_buffer that was allocated for that command. See explanations below. > + } > + } else { > + unsigned char *buf; > + > + buf = kmem_cache_alloc(sense_buffer_slab, __GFP_DMA|gfp_mask); > + if (likely(buf)) { > + memset(cmd, 0, sizeof(*cmd)); > + cmd->sense_buffer = buf; > + } else { > + kmem_cache_free(shost->cmd_pool->slab, cmd); > + cmd = NULL; > + } > } > > return cmd; > @@ -212,7 +231,6 @@ struct scsi_cmnd *scsi_get_command(struct scsi_device *dev, gfp_t gfp_mask) > if (likely(cmd != NULL)) { > unsigned long flags; > > - memset(cmd, 0, sizeof(*cmd)); > cmd->device = dev; > init_timer(&cmd->eh_timeout); > INIT_LIST_HEAD(&cmd->list); > @@ -246,8 +264,10 @@ void __scsi_put_command(struct Scsi_Host *shost, struct scsi_cmnd *cmd, > } > spin_unlock_irqrestore(&shost->free_list_lock, flags); > > - if (likely(cmd != NULL)) > + if (likely(cmd != NULL)) { > + kmem_cache_free(sense_buffer_slab, cmd->sense_buffer); > kmem_cache_free(shost->cmd_pool->slab, cmd); > + } > > put_device(dev); > } > @@ -351,6 +371,49 @@ void scsi_destroy_command_freelist(struct Scsi_Host *shost) > mutex_unlock(&host_cmd_pool_mutex); > } > > +int scsi_setup_command_sense_buffer(struct Scsi_Host *shost) > +{ > + unsigned char *sense_buffer; > + > + mutex_lock(&host_cmd_pool_mutex); > + if (!sense_buffer_slab_users) { > + sense_buffer_slab = kmem_cache_create("scsi_sense_buffer", > + SCSI_SENSE_BUFFERSIZE, > + 0, SLAB_CACHE_DMA, NULL); > + if (!sense_buffer_slab) { > + mutex_unlock(&host_cmd_pool_mutex); > + return -ENOMEM; > + } > + } > + sense_buffer_slab_users++; > + mutex_unlock(&host_cmd_pool_mutex); > + > + sense_buffer = kmem_cache_alloc(sense_buffer_slab, > + GFP_KERNEL | __GFP_DMA); > + if (!sense_buffer) > + goto fail; > + > + shost->backup_sense_buffer = sense_buffer; > + > + return 0; > +fail: > + mutex_lock(&host_cmd_pool_mutex); > + if (!--sense_buffer_slab_users) > + kmem_cache_destroy(sense_buffer_slab); > + mutex_unlock(&host_cmd_pool_mutex); > + return -ENOMEM; > +} > + > +void scsi_destroy_command_sense_buffer(struct Scsi_Host *shost) > +{ > + kmem_cache_free(sense_buffer_slab, shost->backup_sense_buffer); > + > + mutex_lock(&host_cmd_pool_mutex); > + if (!--sense_buffer_slab_users) > + kmem_cache_destroy(sense_buffer_slab); > + mutex_unlock(&host_cmd_pool_mutex); > +} > + > #ifdef CONFIG_SCSI_LOGGING > void scsi_log_send(struct scsi_cmnd *cmd) > { > diff --git a/drivers/scsi/scsi_priv.h b/drivers/scsi/scsi_priv.h > index 3f34e93..55c6f71 100644 > --- a/drivers/scsi/scsi_priv.h > +++ b/drivers/scsi/scsi_priv.h > @@ -27,6 +27,8 @@ extern void scsi_exit_hosts(void); > extern int scsi_dispatch_cmd(struct scsi_cmnd *cmd); > extern int scsi_setup_command_freelist(struct Scsi_Host *shost); > extern void scsi_destroy_command_freelist(struct Scsi_Host *shost); > +extern int scsi_setup_command_sense_buffer(struct Scsi_Host *shost); > +extern void scsi_destroy_command_sense_buffer(struct Scsi_Host *shost); > extern void __scsi_done(struct scsi_cmnd *cmd); > #ifdef CONFIG_SCSI_LOGGING > void scsi_log_send(struct scsi_cmnd *cmd); > diff --git a/include/scsi/scsi_cmnd.h b/include/scsi/scsi_cmnd.h > index 3f47e52..abd7479 100644 > --- a/include/scsi/scsi_cmnd.h > +++ b/include/scsi/scsi_cmnd.h > @@ -88,7 +88,7 @@ struct scsi_cmnd { > working on */ > > #define SCSI_SENSE_BUFFERSIZE 96 > - unsigned char sense_buffer[SCSI_SENSE_BUFFERSIZE]; > + unsigned char *sense_buffer; > /* obtained by REQUEST SENSE when > * CHECK CONDITION is received on original > * command (auto-sense) */ > diff --git a/include/scsi/scsi_host.h b/include/scsi/scsi_host.h > index 0fd4746..65d2bcf 100644 > --- a/include/scsi/scsi_host.h > +++ b/include/scsi/scsi_host.h > @@ -520,6 +520,9 @@ struct Scsi_Host { > struct list_head free_list; /* backup store of cmd structs */ > struct list_head starved_list; > > + /* sense buffer for the backup command */ > + unsigned char *backup_sense_buffer; > + > spinlock_t default_lock; > spinlock_t *host_lock; > commands can be put on the free list in 2 places: [1] void __scsi_put_command(struct Scsi_Host *shost, struct scsi_cmnd *cmd, struct device *dev) { unsigned long flags; /* changing locks here, don't need to restore the irq state */ spin_lock_irqsave(&shost->free_list_lock, flags); if (unlikely(list_empty(&shost->free_list))) { list_add(&cmd->list, &shost->free_list); cmd = NULL; } ... and [2] int scsi_setup_command_freelist(struct Scsi_Host *shost) { ... if (!cmd) goto fail2; list_add(&cmd->list, &shost->free_list); return 0; ... case [1] cmnd had a sense_buffer with it, case [2] did not. The easiest fix would be to remove just the sense buffer from [1] and have an empty cmnd on the free_list in all cases. But I would suggest to just put the extra allocated sense_buffer on the cmnd in case [2] and always have cmnd+sense_buffer, this way you can get rid of the pointer for the backup_sense_buffer in host struct. (and have the code localized to scsi.c only) Also, is there a kmem_cache_zalloc()? I would use it for the command allocation just to make sure when we do scsi_destroy_command_freelist() in the case that a sense_buffer allocation failed and the host is unloaded. Boaz - 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
