linux-kernel - Re: [RFC][PATCH] PM: disable nonboot cpus before suspending devices

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Date:	Mon, 25 Jan 2010 16:08:50 +0100 (CET)
From:	Sebastian Ott <sebott@...ux.vnet.ibm.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
cc:	linux-pm@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: [RFC][PATCH] PM: disable nonboot cpus before suspending
 devices

Hi.

On Fri, 22 Jan 2010, Rafael J. Wysocki wrote:

> On Friday 22 January 2010, Sebastian Ott wrote:
> > 
> > a possible fix would be to call disable_nonboot_cpus before suspending the
> > devices..
> 
> This is going against the changes attempting to speed-up suspend and resume,
> such as the asynchronous suspend/resume patchset, so I don't agree with it.

Isn't the main benefit for this scenario that while a driver starts io and
waits for interrupts, the callback for the next device can be called? And
this can be done with one cpu as well.

> 
> The real solution would be to remove the memory allocations from the
> _cpu_down() call path.

So you have to also ban allocations from all registered notifiers at the
cpu_chain. And since enable_nonboot_cpus is called before the devices are
woken up, the same would be true for _cpu_up() which may not be done
easily.

> 
> BTW, this is one of the cases I and Ben are talking about where it's not
> practical to rework the code just to avoid memory allocation problems during
> suspend/resume.

Ok. All i'm saying is that in hibernation_snapshot/create_image memory
allocations are directely triggered after all devices were put to sleep /
before woken up - and this looks like a bug.

For the driver case - what about using your patch to not modify the gfp
mask but print a warning instead so that these drivers can be identified
and fixed.

Regards,
Sebastian
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