Re: [PATCH v3 20/77] ncr5380: Introduce unbound workqueue
From: Hannes Reinecke
Date: Tue Dec 22 2015 - 09:48:35 EST
On 12/22/2015 01:44 PM, Finn Thain wrote:
On Tue, 22 Dec 2015, Hannes Reinecke wrote:
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?
The polling algorithm I've used requires that the workqueue item is free
to busy-wait and sleep. Perhaps a kthread_worker would be better?
SCSI-2 is pretty much single-threaded, so shifting things onto arbitrary
CPUs don't sound very appealing.
Most of these drivers only run on UP systems. For the x86 drivers, I
suspect that the cache miss penalty would be insignificant compared to
some of the other overheads. The 5380 chip requires that the CPU is
involved in SCSI bus signalling and merely accessing a chip register
takes over a microsecond.
I know.
But using a bound workqueue would mean you could use
'create_workqueue()' instead of open-coding it :-)
But in the end it's up to you. If the thing works I'm not that concerned.
Reviewed-by: Hannes Reinecke <hare@xxxxxxxx>
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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