linux-kernel - Re: Async resume patch (was: Re: [GIT PULL] PM updates for 2.6.33)

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Date:	Wed, 9 Dec 2009 10:57:12 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
cc:	"Rafael J. Wysocki" <rjw@...k.pl>, 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 resume patch (was: Re: [GIT PULL] PM updates for 2.6.33)

On Wed, 9 Dec 2009, Linus Torvalds wrote:

> That's partly why I realy did suggest that we do the async stuff purely in 
> the USB layer, rather than try to put it deeper in the device layer. And 
> if we do support it "natively" in the device layer like Rafael's latest 
> patch, I still think we should be very very nervous about making devices 
> async unless there is a measured - and very noticeable - advantage.

Agreed.  Arjan's measurements indicated that USB was one of the biggest
offenders; everything else other than the PS/2 mouse was much faster.  
Given these results there isn't much incentive to do anything else
asynchronously.

(However other devices not present on Arjan's machine may be a
different story.  Spinning up multiple external disks is a good example 
-- although here it may be necessary for the driver to take charge, 
because spinning up a disk requires a lot of power and doing too many 
of them at the same time could be bad.)

Alan Stern

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