Chris Wilson <ch...@chris-wilson.co.uk> writes:
> As we have pinned the timeline (using tl->active_count), we can safely
> drop the tl->mutex as we wait for what we believe to be the final
> request on that timeline. This is useful for ensuring that we do not
> block the engine heartbeat by hogging the kernel_context's timeline on a
> dead GPU.
>
> References: https://gitlab.freedesktop.org/drm/intel/issues/1364
> Fixes: 058179e72e09 ("drm/i915/gt: Replace hangcheck by heartbeats")
> Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk>
> Cc: Mika Kuoppala <mika.kuopp...@linux.intel.com>
> ---
> drivers/gpu/drm/i915/gt/intel_gt_requests.c | 11 +++++++++--
> 1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gt/intel_gt_requests.c
> b/drivers/gpu/drm/i915/gt/intel_gt_requests.c
> index 8a5054f21bf8..436412d07689 100644
> --- a/drivers/gpu/drm/i915/gt/intel_gt_requests.c
> +++ b/drivers/gpu/drm/i915/gt/intel_gt_requests.c
> @@ -147,24 +147,31 @@ long intel_gt_retire_requests_timeout(struct intel_gt
> *gt, long timeout)
>
> fence = i915_active_fence_get(&tl->last_request);
> if (fence) {
> + mutex_unlock(&tl->mutex);
> +
> timeout = dma_fence_wait_timeout(fence,
> interruptible,
> timeout);
> dma_fence_put(fence);
> +
> + if (!mutex_trylock(&tl->mutex)) {
If you can't take it, it must be active and for the retirement
advancement we can bail out early.
Or is there something else with a sampled try?
> + active_count++;
> + goto out_active;
> + }
> }
> }
>
> if (!retire_requests(tl) || flush_submission(gt))
> active_count++;
> + mutex_unlock(&tl->mutex);
>
> - spin_lock(&timelines->lock);
> +out_active: spin_lock(&timelines->lock);
>
> /* Resume iteration after dropping lock */
You either fixed this comment with this patch.
Or that the comment remains a highly confusing.
> list_safe_reset_next(tl, tn, link);
> if (atomic_dec_and_test(&tl->active_count))
> list_del(&tl->link);
We have the timelines lock and the above seems safe
wtithout the actual mutex.
But the comment is still hauting me.
-Mika
>
> - mutex_unlock(&tl->mutex);
>
> /* Defer the final release to after the spinlock */
> if (refcount_dec_and_test(&tl->kref.refcount)) {
> --
> 2.25.1
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