linux-kernel - Re: [PATCH 1/2] drm/msm: Move hangcheck timer restart

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Date:   Wed, 3 Aug 2022 13:29:02 -0700
From:   Rob Clark <robdclark@...il.com>
To:     Akhil P Oommen <quic_akhilpo@...cinc.com>
Cc:     dri-devel@...ts.freedesktop.org, linux-arm-msm@...r.kernel.org,
        freedreno@...ts.freedesktop.org,
        Rob Clark <robdclark@...omium.org>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] drm/msm: Move hangcheck timer restart

On Wed, Aug 3, 2022 at 12:52 PM Akhil P Oommen <quic_akhilpo@...cinc.com> wrote:
>
> On 8/3/2022 10:53 PM, Rob Clark wrote:
> > From: Rob Clark <robdclark@...omium.org>
> >
> > Don't directly restart the hangcheck timer from the timer handler, but
> > instead start it after the recover_worker replays remaining jobs.
> >
> > If the kthread is blocked for other reasons, there is no point to
> > immediately restart the timer.  Fixes a random symptom of the problem
> > fixed in the next patch.
> >
> > Signed-off-by: Rob Clark <robdclark@...omium.org>
> > ---
> >   drivers/gpu/drm/msm/msm_gpu.c | 14 +++++++++-----
> >   1 file changed, 9 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/msm/msm_gpu.c b/drivers/gpu/drm/msm/msm_gpu.c
> > index fba85f894314..8f9c48eabf7d 100644
> > --- a/drivers/gpu/drm/msm/msm_gpu.c
> > +++ b/drivers/gpu/drm/msm/msm_gpu.c
> > @@ -328,6 +328,7 @@ find_submit(struct msm_ringbuffer *ring, uint32_t fence)
> >   }
> >
> >   static void retire_submits(struct msm_gpu *gpu);
> > +static void hangcheck_timer_reset(struct msm_gpu *gpu);
> >
> >   static void get_comm_cmdline(struct msm_gem_submit *submit, char **comm, char **cmd)
> >   {
> > @@ -420,6 +421,8 @@ static void recover_worker(struct kthread_work *work)
> >       }
> >
> >       if (msm_gpu_active(gpu)) {
> > +             bool restart_hangcheck = false;
> > +
> >               /* retire completed submits, plus the one that hung: */
> >               retire_submits(gpu);
> >
> > @@ -436,10 +439,15 @@ static void recover_worker(struct kthread_work *work)
> >                       unsigned long flags;
> >
> >                       spin_lock_irqsave(&ring->submit_lock, flags);
> > -                     list_for_each_entry(submit, &ring->submits, node)
> > +                     list_for_each_entry(submit, &ring->submits, node) {
> >                               gpu->funcs->submit(gpu, submit);
> > +                             restart_hangcheck = true;
> > +                     }
> >                       spin_unlock_irqrestore(&ring->submit_lock, flags);
> >               }
> > +
> > +             if (restart_hangcheck)
> > +                     hangcheck_timer_reset(gpu);
> >       }
> >
> >       mutex_unlock(&gpu->lock);
> > @@ -515,10 +523,6 @@ static void hangcheck_handler(struct timer_list *t)
> >               kthread_queue_work(gpu->worker, &gpu->recover_work);
> >       }
> >
> > -     /* if still more pending work, reset the hangcheck timer: */
> In the scenario mentioned here, shouldn't we restart the timer?

yeah, actually the case where we don't want to restart the timer is
*only* when we schedule recover_work..

BR,
-R

>
> -Akhil.
> > -     if (fence_after(ring->fctx->last_fence, ring->hangcheck_fence))
> > -             hangcheck_timer_reset(gpu);
> > -
> >       /* workaround for missing irq: */
> >       msm_gpu_retire(gpu);
> >   }
> >
>