linux-kernel - Re: [PATCH v2 5/8] drm/lima: handle spurious timeouts due to high irq latency

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Date: Wed, 24 Jan 2024 20:38:02 +0800
From: Qiang Yu <yuq825@...il.com>
To: Erico Nunes <nunes.erico@...il.com>
Cc: anarsoul@...il.com, christian.koenig@....com, 
	dri-devel@...ts.freedesktop.org, lima@...ts.freedesktop.org, 
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>, 
	Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>, 
	Sumit Semwal <sumit.semwal@...aro.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 5/8] drm/lima: handle spurious timeouts due to high irq latency

On Wed, Jan 24, 2024 at 11:00 AM Erico Nunes <nunes.erico@...il.com> wrote:
>
> There are several unexplained and unreproduced cases of rendering
> timeouts with lima, for which one theory is high IRQ latency coming from
> somewhere else in the system.
> This kind of occurrence may cause applications to trigger unnecessary
> resets of the GPU or even applications to hang if it hits an issue in
> the recovery path.
> Panfrost already does some special handling to account for such
> "spurious timeouts", it makes sense to have this in lima too to reduce
> the chance that it hit users.
>
> Signed-off-by: Erico Nunes <nunes.erico@...il.com>
> ---
>  drivers/gpu/drm/lima/lima_sched.c | 31 ++++++++++++++++++++++++++++---
>  1 file changed, 28 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/lima/lima_sched.c b/drivers/gpu/drm/lima/lima_sched.c
> index c3bf8cda8498..814428564637 100644
> --- a/drivers/gpu/drm/lima/lima_sched.c
> +++ b/drivers/gpu/drm/lima/lima_sched.c
> @@ -1,6 +1,7 @@
>  // SPDX-License-Identifier: GPL-2.0 OR MIT
>  /* Copyright 2017-2019 Qiang Yu <yuq825@...il.com> */
>
> +#include <linux/hardirq.h>
>  #include <linux/iosys-map.h>
>  #include <linux/kthread.h>
>  #include <linux/slab.h>
> @@ -401,9 +402,35 @@ static enum drm_gpu_sched_stat lima_sched_timedout_job(struct drm_sched_job *job
>         struct lima_sched_pipe *pipe = to_lima_pipe(job->sched);
>         struct lima_sched_task *task = to_lima_task(job);
>         struct lima_device *ldev = pipe->ldev;
> +       struct lima_ip *ip = pipe->processor[0];
> +       int i;
> +
> +       /*
> +        * If the GPU managed to complete this jobs fence, the timeout is
> +        * spurious. Bail out.
> +        */
> +       if (dma_fence_is_signaled(task->fence)) {
> +               DRM_WARN("%s spurious timeout\n", lima_ip_name(ip));
> +               return DRM_GPU_SCHED_STAT_NOMINAL;
> +       }
> +
> +       /*
> +        * Lima IRQ handler may take a long time to process an interrupt
> +        * if there is another IRQ handler hogging the processing.
> +        * In order to catch such cases and not report spurious Lima job
> +        * timeouts, synchronize the IRQ handler and re-check the fence
> +        * status.
> +        */
> +       for (i = 0; i < pipe->num_processor; i++)
> +               synchronize_irq(pipe->processor[i]->irq);
> +
I have a question, this timeout handler will be called when GP/PP error IRQ.
If we call synchronize_irq() in the IRQ handler, will we block ourselves here?

> +       if (dma_fence_is_signaled(task->fence)) {
> +               DRM_WARN("%s unexpectedly high interrupt latency\n", lima_ip_name(ip));
> +               return DRM_GPU_SCHED_STAT_NOMINAL;
> +       }
>
>         if (!pipe->error)
> -               DRM_ERROR("lima job timeout\n");
> +               DRM_ERROR("%s job timeout\n", lima_ip_name(ip));
>
>         drm_sched_stop(&pipe->base, &task->base);
>
> @@ -417,8 +444,6 @@ static enum drm_gpu_sched_stat lima_sched_timedout_job(struct drm_sched_job *job
>         if (pipe->bcast_mmu)
>                 lima_mmu_page_fault_resume(pipe->bcast_mmu);
>         else {
> -               int i;
> -
>                 for (i = 0; i < pipe->num_mmu; i++)
>                         lima_mmu_page_fault_resume(pipe->mmu[i]);
>         }
> --
> 2.43.0
>