Re: [PATCH] SATA / AHCI: Do not play with the link PM during suspend to RAM (was: Re: HDD not suspending properly / dead on resume)

From: Rafael J. Wysocki
Date: Mon Aug 02 2010 - 17:39:14 EST

On Monday, August 02, 2010, Stephan Diestelhorst wrote:
> On Wednesday 28 July 2010, 23:50:09 Rafael J. Wysocki wrote:
> > On Saturday, July 10, 2010, Tejun Heo wrote:
> > > On 07/10/2010 08:50 AM, Stephan Diestelhorst wrote:
> > > >> I have a box where this problem is kind of reproducible, but it happens _very_
> > > >> rarely. Also I can't reproduce it on demand running suspend-resume in a tight
> > > >> loop. Are you able to reproduce it more regurarly?
> > > >
> > > > For me it is much more reproducible. If I run multiple direct writing
> > > > dd-s to the disk in question I trigger it rather reliably (~75% or
> > > > higher). See the attached script from an earlier email.
> > > > Maybe that helps triggering your case more reliabl, too?
> > >
> > That didn't help, but the appended patch fixes the problem for me.
> <snip>
> Sorry for taking ages. Vacation and catching up after it are to blame,
> as is me forgetting to build a proper initrd...
> Thanks for the patch! It certainly changes behaviour, however, in a
> very strange way for me. With your patch my machine does not suspend
> to ram anymore (a simple echo mem > /proc/sys/state blocks), and
> nothing happens in dmesg if there is a lot of write I/O while
> suspending. (A number of parallel dd's with oflag=direct)
> If I stop the I/O, the system eventually goes into suspend to RAM.
> However, that takes a while, after the I/O has stopped, and also
> from "Preparing system for suspend" log entry until it is actually
> done.
> Is this intentional?

It surely isn't.

> Let me know how I can debug this further!
> Ideally I'd like to be able to suspend the machine under I/O load,
> too. (E.g. during a compile job.)
> Can you reproduce this at your end, too?

Well, I didn't try suspending with a number of parallel dd's with oflag=direct
in the background, but otherwise I'm not reproducing the issue with
the patch applied.

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