Re: [PATCH 07/14] drm/i915: Stop spinning for DROP_IDLE (debugfs/i915_drop_caches)

Tvrtko Ursulin
2019-05-02T13:34:14Z

On 01/05/2019 12:45, Chris Wilson wrote:
> If the user is racing a call to debugfs/i915_drop_caches with ongoing
> submission from another thread/process, we may never end up idling the
> GPU and be uninterruptibly spinning in debugfs/i915_drop_caches trying
> to catch an idle moment.
>
> Just flush the work once, that should be enough to park the system under
> correct conditions. Outside of those we either have a driver bug or the
> user is racing themselves. Sadly, because the user may be provoking the
> unwanted situation we can't put a warn here to attract attention to a
> probable bug.
>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
> drivers/gpu/drm/i915/i915_debugfs.c | 4 +---
> 1 file changed, 1 insertion(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
> index 7e8898d0b78b..2ecefacb1e66 100644
> --- a/drivers/gpu/drm/i915/i915_debugfs.c
> +++ b/drivers/gpu/drm/i915/i915_debugfs.c
> @@ -3933,9 +3933,7 @@ i915_drop_caches_set(void *data, u64 val)
> fs_reclaim_release(GFP_KERNEL);
>
> if (val & DROP_IDLE) {
> - do {
> - flush_delayed_work(&i915->gem.retire_work);
> - } while (READ_ONCE(i915->gt.awake));
> + flush_delayed_work(&i915->gem.retire_work);
> flush_work(&i915->gem.idle_work);
> }
>
>

What were supposed to be semantics of DROP_IDLE? Now it seems rather
weak. Should it for instance also imply DROP_ACTIVE?

Regards,

Tvrtko