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

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Message-ID: <20091225170943.GB1581@ucw.cz>
Date:	Fri, 25 Dec 2009 18:09:44 +0100
From:	Pavel Machek <pavel@....cz>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	"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)

Hi!

> > 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.)

Well, system would better be able to supply enough current... because
usb disks auto-sleep on their own, and then something like async ls -l
/*/* would kill your machine...
								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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