On Wed, 2022-08-10 at 13:59 +0200, Karol Herbst wrote:
> On Wed, Aug 10, 2022 at 12:42 PM Computer Enthusiastic
> <computer.enthusiastic@xxxxxxxxx> wrote:
> >
> > Hello,
> >
> > The "supend to ram" issue (system freeze when resuming after suspend
> > to ram or disk hibernation) is still affecting the nouveau kernel
> > module from linux version 5 and above with nvidia GeForce 9600M GT and
> > other nvidia graphic card with the same chipset [1][2][3].
> >
> > I've been successfully using the "work in progress" patch by Karol
> > Herbst [4] to solve the "supend to ram" issue since it was proposed
> > for an apparent different issue ("[GT216][Linux 5.16.4] Long stalls in
> > dma_fence_default_wait") [5] whose root cause is probably the same.
> >
> > I send this message to bring to your attention the aforementioned
> > patch [4] (below in the message as text) to evaluate it for the next
> > steps for possible inclusion in the upstream kernel version.
> >
>
> I think it might be better to CC Ben and Lyude, who _might_ have a
> good idea on what's the proper patch, but maybe the patch is fine as
> it is?
When the GPU starts going into suspend, TTM migrates all of the active bos in
vram over to system ram so they aren't lost. Based on what's described here
and the fact that a fence wait seems to fix it, it sounds like to me that TTM
may still be migrating bos (buffer objects) from the GPU over to system RAM
when the suspend process starts. Of course this causes those operations to get
interrupted and lose access to VRAM unexpectedly, which likely causes the
world to go boom.
So, I'm not 100% sure but I think this patch is potentially overkill since it
looks like it would fix this issue by just making all m2mf bo moves
synchronous. Thisis something we probably(?) don't want to do since if my
theory is correct, the only time we should need to do a fence wait is before
suspending the GPU in order to ensure that all m2mf operations have been
completed before continuing suspend. I think Ben would likely need to weigh
in, or you might be able to figure out the answer to this just by seeing how
we handle this with the newer method of vram blitting - the CE (copy engine).
Let me know if you need any more input, or are able to come up with a patch
that more or less does what I just described.
>
> > Thanks.
> >
> > [1] https://gitlab.freedesktop.org/xorg/driver/xf86-video-nouveau/-/issues/547
> > [2] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=989705#5
> > [3] https://bugzilla.kernel.org/show_bug.cgi?id=213617
> > [4] https://gitlab.freedesktop.org/drm/nouveau/-/issues/156#note_1385770
> > [5] https://gitlab.freedesktop.org/drm/nouveau/-/issues/156
> >
> > ----- %= ----- %= ----- %=
> >
> > From 70271cb0aa30e4523d39c3942e84b16fe18338f5 Mon Sep 17 00:00:00 2001
> > From: Karol Herbst <kherbst@xxxxxxxxxx>
> > Date: Mon, 16 May 2022 17:40:20 +0200
> > Subject: [PATCH] nouveau WIP
> >
> > ---
> > drivers/gpu/drm/nouveau/nouveau_bo.c | 1 +
> > 1 file changed, 1 insertion(+)
> >
> > diff --git a/drivers/gpu/drm/nouveau/nouveau_bo.c
> > b/drivers/gpu/drm/nouveau/nouveau_bo.c
> > index 05076e530e7d..b6343741eda6 100644
> > --- a/drivers/gpu/drm/nouveau/nouveau_bo.c
> > +++ b/drivers/gpu/drm/nouveau/nouveau_bo.c
> > @@ -820,6 +820,7 @@ nouveau_bo_move_m2mf(struct ttm_buffer_object *bo,
> > int evict,
> > if (ret == 0) {
> > ret = nouveau_fence_new(chan, false, &fence);
> > if (ret == 0) {
> > + nouveau_fence_wait(fence, false, false);
> > ret = ttm_bo_move_accel_cleanup(bo,
> > &fence->base,
> > evict, false,
> > --
> > 2.35.3
> >
>
--
Cheers,
Lyude Paul (she/her)
Software Engineer at Red Hat
