linux-kernel - Re: [PATCH v1] PM: sleep: Restore asynchronous device resume optimization

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Date: Wed, 7 Feb 2024 19:41:32 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Tejun Heo <tj@...nel.org>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>, Marek Szyprowski <m.szyprowski@...sung.com>, 
	"Rafael J. Wysocki" <rjw@...ysocki.net>, Linux PM <linux-pm@...r.kernel.org>, 
	Ulf Hansson <ulf.hansson@...aro.org>, Nathan Chancellor <nathan@...nel.org>, 
	LKML <linux-kernel@...r.kernel.org>, 
	Stanislaw Gruszka <stanislaw.gruszka@...ux.intel.com>, Lai Jiangshan <jiangshanlai@...il.com>, 
	Naohiro.Aota@....com, kernel-team@...a.com
Subject: Re: [PATCH v1] PM: sleep: Restore asynchronous device resume optimization

On Wed, Feb 7, 2024 at 5:40 PM Tejun Heo <tj@...nel.org> wrote:
>
> Hello,
>
> On Wed, Feb 07, 2024 at 12:25:46PM +0100, Rafael J. Wysocki wrote:
> > The other one is that what happens during async resume does not meet
> > the assumptions of commit 5797b1c18919 (for example, it can easily
> > produce a chain of interdependent work items longer than 8) and so it
> > breaks things.
>
> Ah, that's fascinating. But aren't CPUs all brought up online before devices
> are resumed?

They are.

> If so, the max_active should already be way higher than the
> WQ_DFL_MIN_ACTIVE. Also, are these multi node NUMA machines?

They aren't.

> Otherwise, it really shouldn't affect anything.

Well, it evidently makes a difference.  I'm wondering what difference
it can make in that case.

> One easy way to verify would be just bumping up WQ_DFL_MIN_ACTIVE and see what happens.

Sure.