[PATCH RESEND] IB/device: Convert ib-comp-wq to be CPU-bound

[PATCH RESEND] IB/device: Convert ib-comp-wq to be CPU-bound

[Sagi Grimberg]

This workqueue is used by our storage target mode ULPs
via the new CQ API. Recent observations when working
with very high-end flash storage devices reveal that
UNBOUND workqueue threads can migrate between cpu cores
and even numa nodes (although some numa locality is accounted
for).

While this attribute can be useful in some workloads,
it does not fit in very nicely with the normal
run-to-completion model we usually use in our target-mode
ULPs and the block-mq irq<->cpu affinity facilities.

The whole block-mq concept is that the completion will
land on the same cpu where the submission was performed.
The fact that our submitter thread is migrating cpus
can break this locality.

We assume that as a target mode ULP, we will serve multiple
initiators/clients and we can spread the load enough without
having to use unbound kworkers.

Also, while we're at it, expose this workqueue via sysfs which
is harmless and can be useful for debug.

Signed-off-by: Sagi Grimberg <sagi-NQWnxTmZq1alnMjI0IkVqw@public.gmane.org>
---
 drivers/infiniband/core/device.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/infiniband/core/device.c b/drivers/infiniband/core/device.c
index 593d2ce6ec7c..fb5ae9564e80 100644
--- a/drivers/infiniband/core/device.c
+++ b/drivers/infiniband/core/device.c
@@ -1015,8 +1015,7 @@ static int __init ib_core_init(void)
 		return -ENOMEM;
 
 	ib_comp_wq = alloc_workqueue("ib-comp-wq",
-			WQ_UNBOUND | WQ_HIGHPRI | WQ_MEM_RECLAIM,
-			WQ_UNBOUND_MAX_ACTIVE);
+			WQ_HIGHPRI | WQ_MEM_RECLAIM | WQ_SYSFS, 0);
 	if (!ib_comp_wq) {
 		ret = -ENOMEM;
 		goto err;
-- 
2.7.4

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Re: [PATCH RESEND] IB/device: Convert ib-comp-wq to be CPU-bound

[Christoph Hellwig]

This looks fine in principle, but any performance number showing
how this helps (or at least doesn't hurt)?
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Re: [PATCH RESEND] IB/device: Convert ib-comp-wq to be CPU-bound

[Bart Van Assche]

On Wed, 2017-03-08 at 22:03 +0200, Sagi Grimberg wrote:
> [ ... ]

Reviewed-by: Bart Van Assche <bart.vanassche-XdAiOPVOjttBDgjK7y7TUQ@public.gmane.org>--
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Re: [PATCH RESEND] IB/device: Convert ib-comp-wq to be CPU-bound

[Sagi Grimberg]

> This looks fine in principle, but any performance number showing
> how this helps (or at least doesn't hurt)?

I had it back when I noticed it and came up with this patch,
but it was a while ago... Also, IIRC Ming ran it at some point.

I'll rerun it though.
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Re: [PATCH RESEND] IB/device: Convert ib-comp-wq to be CPU-bound

[Doug Ledford]

On Wed, 2017-03-08 at 22:03 +0200, Sagi Grimberg wrote:
> This workqueue is used by our storage target mode ULPs
> via the new CQ API. Recent observations when working
> with very high-end flash storage devices reveal that
> UNBOUND workqueue threads can migrate between cpu cores
> and even numa nodes (although some numa locality is accounted
> for).
> 
> While this attribute can be useful in some workloads,
> it does not fit in very nicely with the normal
> run-to-completion model we usually use in our target-mode
> ULPs and the block-mq irq<->cpu affinity facilities.
> 
> The whole block-mq concept is that the completion will
> land on the same cpu where the submission was performed.
> The fact that our submitter thread is migrating cpus
> can break this locality.
> 
> We assume that as a target mode ULP, we will serve multiple
> initiators/clients and we can spread the load enough without
> having to use unbound kworkers.
> 
> Also, while we're at it, expose this workqueue via sysfs which
> is harmless and can be useful for debug.
> 
> Signed-off-by: Sagi Grimberg <sagi-NQWnxTmZq1alnMjI0IkVqw@public.gmane.org>

Thanks, applied.

-- 
Doug Ledford <dledford-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
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