linux-kernel - Re: [PATCH 2/3] drm/msm/gpu: Park scheduler threads for system suspend

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Date:   Thu, 17 Mar 2022 09:18:44 -0700
From:   Rob Clark <robdclark@...il.com>
To:     Christian König <christian.koenig@....com>
Cc:     Andrey Grodzovsky <andrey.grodzovsky@....com>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        freedreno <freedreno@...ts.freedesktop.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Rob Clark <robdclark@...omium.org>,
        Sean Paul <sean@...rly.run>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        David Airlie <airlied@...ux.ie>,
        Akhil P Oommen <quic_akhilpo@...cinc.com>,
        Jonathan Marek <jonathan@...ek.ca>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Vladimir Lypak <vladimir.lypak@...il.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] drm/msm/gpu: Park scheduler threads for system suspend

On Thu, Mar 17, 2022 at 9:04 AM Christian König
<christian.koenig@....com> wrote:
>
> Am 17.03.22 um 16:10 schrieb Rob Clark:
> > [SNIP]
> > userspace frozen != kthread frozen .. that is what this patch is
> > trying to address, so we aren't racing between shutting down the hw
> > and the scheduler shoveling more jobs at us.
>
> Well exactly that's the problem. The scheduler is supposed to shoveling
> more jobs at us until it is empty.
>
> Thinking more about it we will then keep some dma_fence instance
> unsignaled and that is and extremely bad idea since it can lead to
> deadlocks during suspend.

Hmm, perhaps that is true if you need to migrate things out of vram?
It is at least not a problem when vram is not involved.

> So this patch here is an absolute clear NAK from my side. If amdgpu is
> doing something similar that is a severe bug and needs to be addressed
> somehow.

I think amdgpu's use of kthread_park is not related to suspend, but
didn't look too closely.

And perhaps the solution for this problem is more complex in the case
of amdgpu, I'm not super familiar with the constraints there.  But I
think it is a fine solution for integrated GPUs.

BR,
-R

> Regards,
> Christian.
>
> >
> > BR,
> > -R
> >
>