linux-kernel - Re: [PATCH] DRM / radeon / PM: Do not evict VRAM during freeze phase of hibernation

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Message-Id: <201006191453.58379.rjw@sisk.pl>
Date:	Sat, 19 Jun 2010 14:53:58 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Dave Airlie <airlied@...hat.com>
Cc:	linux-kernel@...r.kernel.org,
	"dri-devel" <dri-devel@...ts.freedesktop.org>,
	linux-pm@...ts.linux-foundation.org,
	Alex Deucher <alexdeucher@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ondrej Zary <linux@...nbow-software.org>
Subject: Re: [PATCH] DRM / radeon / PM: Do not evict VRAM during freeze phase of hibernation

On Saturday, June 19, 2010, Dave Airlie wrote:
> On Sat, 2010-06-19 at 01:23 +0200, Rafael J. Wysocki wrote:
> > On Friday, June 18, 2010, Dave Airlie wrote:
> > > On Fri, 2010-06-18 at 22:21 +0200, Rafael J. Wysocki wrote:
> > > > From: Rafael J. Wysocki <rjw@...k.pl>
> > > > 
> > > > I have recently noticed a 55 sec. delay during the "device freeze"
> > > > phase of hibernation on my test-bed HP nx6325.  Due to the 100%
> > > > reproducibility of it I was able to narrow it down to
> > > > radeon_suspend_kms() and then it turned out that the delay occured
> > > > somewhere in radeon_bo_evict_vram().  However, it doesn't seem really
> > > > necessary or even very useful to me to evict VRAM at this particular
> > > > point, because we're going to create an image and bring the device
> > > > back to the fully functional state in a little while.  Thus, I think
> > > > the VRAM evicition can be skipped for state.event == PM_EVENT_FREEZE,
> > > > which makes the delay go away.
> > > 
> > > I'm not 100% sure of the hibernate sequencing and its early in the
> > > morning, but we want to evict VRAM before image building so we can have
> > > the contents of VRAM in the image so we can restore them on resume. Does
> > > this just avoid evicting them a second time after we created the image?
> > 
> > No, it's the first time, before creating the image, but I didn't seen any
> > difference on resume with and without the patch, so I thought it was a good
> > idea. :-)
> 
> On the machine you have its most likely not going to show up unless you
> are running a 3D app or something across suspend, since currently X
> re-exposes most apps on VT switch, so they just redraw.

Yes.  Moreover, hibernation is always done after a VT switch.  That's why
I said I thought the eviction wasn't necessary in the changelog.

BTW, I have three different test boxes with radeon hardware and the
$subject patch is not a problem on any of them.

> Was it always this slow?

Nope.  It definitely is a regression, although I'm not sure what's the last
good kernel.

> you can see how many objects are in vram using
> debugfs (/sys/kernel/debug/dri/0/radeon_vram_mm), it sounds like the TTM
> eviction process is blocking on something,

Yup.

> we shouldn't be using any UC/WC memory on that machine so I can't imagine
> the new pool allocator stuff would get in the way. Maybe its the lack of
> GFP_USER, (Jerome posted a patch).

Can you give me a pointer to that patch, please?

Rafael
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