On Wed, 2025-06-18 at 11:47 -0300, Maíra Canal wrote:
> When the DRM scheduler times out, it's possible that the GPU isn't
> hung;
> instead, a job may still be running, and there may be no valid reason
> to
> reset the hardware. This can occur in two situations:
>
> 1. The GPU exposes some mechanism that ensures the GPU is still
> making
> progress. By checking this mechanism, the driver can safely skip
> the
> reset, re-arm the timeout, and allow the job to continue running
> until
> completion. This is the case for v3d, Etnaviv, and Xe.
> 2. Timeout has fired before the free-job worker. Consequently, the
> scheduler calls `timedout_job()` for a job that isn't timed out.
Optional nit: I'd hint here that timedout_job() is a driver callback.
>
> These two scenarios are problematic because the job was removed from
> the
> `sched->pending_list` before calling `sched->ops->timedout_job()`,
> which
> means that when the job finishes, it won't be freed by the scheduler
> though `sched->ops->free_job()` - leading to a memory leak.
>
> To solve those problems, create a new `drm_gpu_sched_stat`, called
> DRM_GPU_SCHED_STAT_NO_HANG, that allows a driver to skip the reset.
> The
> new status will indicate that the job must be reinserted into the
> pending list, and the hardware / driver will still complete that job.
>
> Signed-off-by: Maíra Canal <mca...@igalia.com>
> ---
> drivers/gpu/drm/scheduler/sched_main.c | 43
> ++++++++++++++++++++++++++++++++--
> include/drm/gpu_scheduler.h | 3 +++
> 2 files changed, 44 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/scheduler/sched_main.c
> b/drivers/gpu/drm/scheduler/sched_main.c
> index
> fb6d9eddf5b378910b66d456f3610ff2ca7c0f41..5e1c07ca867cb14746cec9a7e53
> 896fe17af6e58 100644
> --- a/drivers/gpu/drm/scheduler/sched_main.c
> +++ b/drivers/gpu/drm/scheduler/sched_main.c
> @@ -380,11 +380,16 @@ static void drm_sched_run_free_queue(struct
> drm_gpu_scheduler *sched)
> {
> struct drm_sched_job *job;
>
> - spin_lock(&sched->job_list_lock);
> job = list_first_entry_or_null(&sched->pending_list,
> struct drm_sched_job, list);
> if (job && dma_fence_is_signaled(&job->s_fence->finished))
> __drm_sched_run_free_queue(sched);
> +}
> +
> +static void drm_sched_run_free_queue_unlocked(struct
> drm_gpu_scheduler *sched)
> +{
> + spin_lock(&sched->job_list_lock);
> + drm_sched_run_free_queue(sched);
> spin_unlock(&sched->job_list_lock);
> }
>
> @@ -537,6 +542,31 @@ static void drm_sched_job_begin(struct
> drm_sched_job *s_job)
> spin_unlock(&sched->job_list_lock);
> }
>
> +/**
> + * drm_sched_job_reinsert_on_false_timeout - Reinsert the job on a
nit: The other docstrings all start with lower case after the -
> false timeout
> + * @sched: scheduler instance
> + * @job: job to be reinserted on the pending list
> + *
> + * In the case of a "false timeout" - when a timeout occurs but the
> GPU isn't
> + * hung and the job is making progress, the scheduler must reinsert
> the job back
> + * into the pending list. Otherwise, the job and its resources won't
> be freed
> + * through the &drm_sched_backend_ops.free_job callback.
> + *
> + * Note that after reinserting the job, the scheduler enqueues the
> free-job
> + * work again if ready. Otherwise, a signaled job could be added to
> the pending
> + * list, but never freed.
> + *
> + * This function must be used in "false timeout" cases only.
> + */
> +static void drm_sched_job_reinsert_on_false_timeout(struct
> drm_gpu_scheduler *sched,
> + struct
> drm_sched_job *job)
> +{
> + spin_lock(&sched->job_list_lock);
> + list_add(&job->list, &sched->pending_list);
> + drm_sched_run_free_queue(sched);
> + spin_unlock(&sched->job_list_lock);
> +}
> +
> static void drm_sched_job_timedout(struct work_struct *work)
> {
> struct drm_gpu_scheduler *sched;
> @@ -570,6 +600,9 @@ static void drm_sched_job_timedout(struct
> work_struct *work)
> job->sched->ops->free_job(job);
> sched->free_guilty = false;
> }
> +
> + if (status == DRM_GPU_SCHED_STAT_NO_HANG)
> + drm_sched_job_reinsert_on_false_timeout(sche
> d, job);
> } else {
> spin_unlock(&sched->job_list_lock);
> }
> @@ -592,6 +625,9 @@ static void drm_sched_job_timedout(struct
> work_struct *work)
> * This function is typically used for reset recovery (see the docu
> of
> * drm_sched_backend_ops.timedout_job() for details). Do not call it
> for
> * scheduler teardown, i.e., before calling drm_sched_fini().
> + *
> + * As it's used for reset recovery, drm_sched_stop() shouldn't be
> called
> + * if the driver skipped the reset (DRM_GPU_SCHED_STAT_NO_HANG).
> */
> void drm_sched_stop(struct drm_gpu_scheduler *sched, struct
> drm_sched_job *bad)
> {
> @@ -677,6 +713,9 @@ EXPORT_SYMBOL(drm_sched_stop);
> * drm_sched_backend_ops.timedout_job() for details). Do not call it
> for
> * scheduler startup. The scheduler itself is fully operational
> after
> * drm_sched_init() succeeded.
> + *
> + * As it's used for reset recovery, drm_sched_start() shouldn't be
> called
> + * if the driver skipped the reset (DRM_GPU_SCHED_STAT_NO_HANG).
> */
> void drm_sched_start(struct drm_gpu_scheduler *sched, int errno)
> {
> @@ -1198,7 +1237,7 @@ static void drm_sched_free_job_work(struct
> work_struct *w)
> if (job)
> sched->ops->free_job(job);
>
> - drm_sched_run_free_queue(sched);
> + drm_sched_run_free_queue_unlocked(sched);
> drm_sched_run_job_queue(sched);
> }
>
> diff --git a/include/drm/gpu_scheduler.h
> b/include/drm/gpu_scheduler.h
> index
> 83e5c00d8dd9a83ab20547a93d6fc572de97616e..423bcc7d7584d3f85cc5a10982f
> 3cf637a781825 100644
> --- a/include/drm/gpu_scheduler.h
> +++ b/include/drm/gpu_scheduler.h
> @@ -393,11 +393,14 @@ struct drm_sched_job {
> * @DRM_GPU_SCHED_STAT_NONE: Reserved. Do not use.
> * @DRM_GPU_SCHED_STAT_RESET: The GPU hung and successfully reset.
> * @DRM_GPU_SCHED_STAT_ENODEV: Error: Device is not available
> anymore.
> + * @DRM_GPU_SCHED_STAT_NO_HANG: Contrary to scheduler's belief, the
> GPU
> + * did not hang and is operational.
Maybe
s/belief/assumption
and
s/operational/still running
Up to you, I think either is fine.
Code itself looks good.
P.
> */
> enum drm_gpu_sched_stat {
> DRM_GPU_SCHED_STAT_NONE,
> DRM_GPU_SCHED_STAT_RESET,
> DRM_GPU_SCHED_STAT_ENODEV,
> + DRM_GPU_SCHED_STAT_NO_HANG,
> };
>
> /**
>
