linux-kernel - Re: Async suspend-resume patch w/ completions (was: Re: Async suspend-resume patch w/ rwsems)

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Date:	Tue, 15 Dec 2009 07:26:41 -0800 (PST)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
cc:	Alan Stern <stern@...land.harvard.edu>,
	Zhang Rui <rui.zhang@...el.com>,
	LKML <linux-kernel@...r.kernel.org>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	pm list <linux-pm@...ts.linux-foundation.org>
Subject: Re: Async suspend-resume patch w/ completions (was: Re: Async
 suspend-resume patch w/ rwsems)

On Tue, 15 Dec 2009, Rafael J. Wysocki wrote:
> > 
> > Give a real example that matters.
> 
> I'll try.  Let -> denote child-parent relationships and assume dpm_list looks
> like this:

No. 

I mean something real - something like

 - if you run on a non-PC with two USB buses behind non-PCI controllers.

 - device xyz.

> If this applies to _resume_ only, then I agree, but the Arjan's data clearly
> show that serio devices take much more time to suspend than USB.

I mean in general - something where you actually have hard data that some 
device really needs anythign more than my one-liner, and really _needs_ 
some complex infrastructure.

Not "let's imagine a case like xyz".

> But if we only talk about resume, the PCI bridges don't really matter,
> because they are resumed before all devices that depend on them, so they don't
> really need to wait for anyone anyway.

But that's my _point_. That's the whole point of the one-liner patch. Read 
the comment above that one-liner.

My whole point was that by doing the whole "wait for children" in generic 
code, you also made devices - such as PCI bridges - have to wait for 
children, even though they don't need to, and don't want to.

So I suggested an admittedly ugly hack to take care of it - rather than 
some complex infrastructure.

		Linus
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