linux-kernel - Re: Selecting CPUs for queuing work on

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Message-ID: <Yva4g3V2jAP0NKcY@slm.duckdns.org>
Date:   Fri, 12 Aug 2022 10:30:59 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Felix Kuehling <felix.kuehling@....com>
Cc:     Lai Jiangshan <jiangshanlai@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Dave Airlie <airlied@...il.com>,
        Philip Yang <Philip.Yang@....com>,
        Maling list - DRI developers 
        <dri-devel@...ts.freedesktop.org>,
        "amd-gfx@...ts.freedesktop.org" <amd-gfx@...ts.freedesktop.org>
Subject: Re: Selecting CPUs for queuing work on

On Fri, Aug 12, 2022 at 04:26:47PM -0400, Felix Kuehling wrote:
> Hi workqueue maintainers,
> 
> In the KFD (amdgpu) driver we found a need to schedule bottom half interrupt
> handlers on CPU cores different from the one where the top-half interrupt
> handler runs to avoid the interrupt handler stalling the bottom half in
> extreme scenarios. See my latest patch that tries to use a different
> hyperthread on the same CPU core, or falls back to a different core in the
> same NUMA node if that fails:
> https://lore.kernel.org/all/20220811190433.1213179-1-Felix.Kuehling@amd.com/
> 
> Dave pointed out that the driver may not be the best place to implement such
> logic and suggested that we should have an abstraction, maybe in the
> workqueue code. Do you feel this is something that could or should be
> provided by the core workqueue code? Or maybe some other place?

I'm not necessarily against it. I guess it can be a flag on an unbound wq.
Do the interrupts move across different CPUs tho? ie. why does this need to
be a dynamic decision?

Thanks.

-- 
tejun