linux-kernel - Re: [PATCHSET v1 wq/for-6.5] workqueue: Improve unbound workqueue execution locality

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Date:   Mon, 12 Jun 2023 16:48:07 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Brian Norris <briannorris@...omium.org>
Cc:     jiangshanlai@...il.com, torvalds@...ux-foundation.org,
        peterz@...radead.org, linux-kernel@...r.kernel.org,
        kernel-team@...a.com, joshdon@...gle.com, brho@...gle.com,
        nhuck@...gle.com, agk@...hat.com, snitzer@...nel.org,
        void@...ifault.com, treapking@...omium.org
Subject: Re: [PATCHSET v1 wq/for-6.5] workqueue: Improve unbound workqueue
 execution locality

Hello,

On Mon, Jun 12, 2023 at 04:56:06PM -0700, Brian Norris wrote:
> Thanks for the CC; my colleague tried out your patches (ported to 5.15
> with some minor difficulty), and aside from some crashes (already noted
> by others, although we didn't pull the proposed v2 fixes), he didn't

Yeah, there were a few subtle bugs that v2 fixes.

> notice a significant change in performance on our particular test system
> and WiFi-throughput workload. I don't think we expected a lot though,
> per the discussion at:
> 
> https://lore.kernel.org/all/ZFvpJb9Dh0FCkLQA@google.com/

That's disappointing. I was actually expecting that the default behavior
would restrain migrations across L3 boundaries strong enough to make a
meaningful difference. Can you enable WQ_SYSFS and test the following
configs?

 1. affinity_scope = cache, affinity_strict = 1

 2. affinity_scope = cpu, affinity_strict = 0

 3. affinity_scope = cpu, affinity_strict = 1

#3 basically turns it into a percpu workqueue, so it should perform more or
less the same as a percpu workqueue without affecting everyone else.

Any chance you can post the toplogy details on the affected setup? How are
the caches and cores laid out?

Thanks.

-- 
tejun