Re: [PATCH v3 20/77] ncr5380: Introduce unbound workqueue

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On 12/22/2015 02:17 AM, Finn Thain wrote:
Allocate a work queue that will permit busy waiting and sleeping. This
means NCR5380_init() can potentially fail, so add this error path.

Signed-off-by: Finn Thain <fthain@xxxxxxxxxxxxxxxxxxx>

---

In subsequent patches, the work function adopts this work queue so it
can sleep while polling, which allows the removal of some flawed and
complicated code in NCR5380_select() in NCR5380.c.

Changed since v1:
- Dropped WQ_CPU_INTENSIVE flag because Documentation/workqueue.txt says it
   "is meaningless for unbound wq".

---
  drivers/scsi/NCR5380.c       |   15 +++++++++++----
  drivers/scsi/NCR5380.h       |    1 +
  drivers/scsi/arm/cumana_1.c  |    8 ++++++--
  drivers/scsi/arm/oak.c       |    8 ++++++--
  drivers/scsi/atari_NCR5380.c |    8 +++++++-
  drivers/scsi/atari_scsi.c    |    5 ++++-
  drivers/scsi/dmx3191d.c      |   17 +++++++++++------
  drivers/scsi/dtc.c           |   11 +++++++++--
  drivers/scsi/g_NCR5380.c     |   31 +++++++++++++++----------------
  drivers/scsi/mac_scsi.c      |    5 ++++-
  drivers/scsi/pas16.c         |   10 ++++++++--
  drivers/scsi/sun3_scsi.c     |    5 ++++-
  drivers/scsi/t128.c          |   13 ++++++++++---
  13 files changed, 96 insertions(+), 41 deletions(-)

Index: linux/drivers/scsi/NCR5380.c
===================================================================
--- linux.orig/drivers/scsi/NCR5380.c	2015-12-22 12:15:52.000000000 +1100
+++ linux/drivers/scsi/NCR5380.c	2015-12-22 12:15:56.000000000 +1100
@@ -514,7 +514,7 @@ static int should_disconnect(unsigned ch
  static void NCR5380_set_timer(struct NCR5380_hostdata *hostdata, unsigned long timeout)
  {
  	hostdata->time_expires = jiffies + timeout;
-	schedule_delayed_work(&hostdata->coroutine, timeout);
+	queue_delayed_work(hostdata->work_q, &hostdata->coroutine, timeout);
  }


@@ -791,7 +791,12 @@ static int NCR5380_init(struct Scsi_Host
  	hostdata->disconnected_queue = NULL;
  	
  	INIT_DELAYED_WORK(&hostdata->coroutine, NCR5380_main);
-	
+	hostdata->work_q = alloc_workqueue("ncr5380_%d",
+	                        WQ_UNBOUND | WQ_MEM_RECLAIM,
+	                        1, instance->host_no);
+	if (!hostdata->work_q)
+		return -ENOMEM;
+
  	/* The CHECK code seems to break the 53C400. Will check it later maybe */
  	if (flags & FLAG_NCR53C400)
  		hostdata->flags = FLAG_HAS_LAST_BYTE_SENT | flags;

Wouldn't it be better to use a normal (ie bound) workqueue here?
SCSI-2 is pretty much single-threaded, so shifting things onto arbitrary CPUs don't sound very appealing.

Cheers,

Hannes
--
Dr. Hannes Reinecke		      zSeries & Storage
hare@xxxxxxx			      +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg)
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