On Tue, 2019-10-08 at 11:56 +0100, Chris Wilson wrote:
> A common bane of ours is arbitrary delays in ksoftirqd processing our
> submission tasklet. Give the submission tasklet a kick before we wait
> to
> avoid those delays eating into a tight timeout.
>
> Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk>
> ---
> drivers/gpu/drm/i915/gt/intel_engine.h | 3 +-
> drivers/gpu/drm/i915/gt/intel_engine_cs.c | 33 +++++++++++++----
> ----
> drivers/gpu/drm/i915/gt/intel_gt_requests.c | 12 ++++++++
> 3 files changed, 34 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gt/intel_engine.h
> b/drivers/gpu/drm/i915/gt/intel_engine.h
> index c9e8c8ccbd47..d624752f2a92 100644
> --- a/drivers/gpu/drm/i915/gt/intel_engine.h
> +++ b/drivers/gpu/drm/i915/gt/intel_engine.h
> @@ -407,8 +407,9 @@ static inline void __intel_engine_reset(struct
> intel_engine_cs *engine,
> engine->serial++; /* contexts lost */
> }
>
> -bool intel_engine_is_idle(struct intel_engine_cs *engine);
> bool intel_engines_are_idle(struct intel_gt *gt);
> +bool intel_engine_is_idle(struct intel_engine_cs *engine);
> +void intel_engine_flush_submission(struct intel_engine_cs *engine);
>
> void intel_engines_reset_default_submission(struct intel_gt *gt);
>
> diff --git a/drivers/gpu/drm/i915/gt/intel_engine_cs.c
> b/drivers/gpu/drm/i915/gt/intel_engine_cs.c
> index 6220b7151bb9..7e2aa7a6bef0 100644
> --- a/drivers/gpu/drm/i915/gt/intel_engine_cs.c
> +++ b/drivers/gpu/drm/i915/gt/intel_engine_cs.c
> @@ -1040,6 +1040,25 @@ static bool ring_is_idle(struct
> intel_engine_cs *engine)
> return idle;
> }
>
> +void intel_engine_flush_submission(struct intel_engine_cs *engine)
> +{
> + struct tasklet_struct *t = &engine->execlists.tasklet;
> +
> + if (__tasklet_is_scheduled(t)) {
> + local_bh_disable();
> + if (tasklet_trylock(t)) {
> + /* Must wait for any GPU reset in progress. */
> + if (__tasklet_is_enabled(t))
> + t->func(t->data);
> + tasklet_unlock(t);
> + }
> + local_bh_enable();
> + }
> +
> + /* Otherwise flush the tasklet if it was running on another cpu
> */
> + tasklet_unlock_wait(t);
> +}
> +
> /**
> * intel_engine_is_idle() - Report if the engine has finished
> process all work
> * @engine: the intel_engine_cs
> @@ -1058,21 +1077,9 @@ bool intel_engine_is_idle(struct
> intel_engine_cs *engine)
>
> /* Waiting to drain ELSP? */
> if (execlists_active(&engine->execlists)) {
> - struct tasklet_struct *t = &engine->execlists.tasklet;
> -
> synchronize_hardirq(engine->i915->drm.pdev->irq);
>
> - local_bh_disable();
> - if (tasklet_trylock(t)) {
> - /* Must wait for any GPU reset in progress. */
> - if (__tasklet_is_enabled(t))
> - t->func(t->data);
> - tasklet_unlock(t);
> - }
> - local_bh_enable();
> -
> - /* Otherwise flush the tasklet if it was on another cpu
> */
> - tasklet_unlock_wait(t);
> + intel_engine_flush_submission(engine);
>
> if (execlists_active(&engine->execlists))
> return false;
> diff --git a/drivers/gpu/drm/i915/gt/intel_gt_requests.c
> b/drivers/gpu/drm/i915/gt/intel_gt_requests.c
> index ca606b79fd5e..cbb4069b11e1 100644
> --- a/drivers/gpu/drm/i915/gt/intel_gt_requests.c
> +++ b/drivers/gpu/drm/i915/gt/intel_gt_requests.c
> @@ -4,6 +4,7 @@
> * Copyright © 2019 Intel Corporation
> */
>
> +#include "i915_drv.h" /* for_each_engine() */
> #include "i915_request.h"
> #include "intel_gt.h"
> #include "intel_gt_pm.h"
> @@ -19,6 +20,15 @@ static void retire_requests(struct intel_timeline
> *tl)
> break;
> }
>
> +static void flush_submission(struct intel_gt *gt)
> +{
> + struct intel_engine_cs *engine;
> + enum intel_engine_id id;
> +
> + for_each_engine(engine, gt->i915, id)
> + intel_engine_flush_submission(engine);
> +}
> +
> long intel_gt_retire_requests_timeout(struct intel_gt *gt, long
> timeout)
> {
> struct intel_gt_timelines *timelines = >->timelines;
> @@ -32,6 +42,8 @@ long intel_gt_retire_requests_timeout(struct
> intel_gt *gt, long timeout)
> if (unlikely(timeout < 0))
> timeout = -timeout, interruptible = false;
>
> + flush_submission(gt); /* kick the ksoftirqd tasklets */
Won't this add a performance hit if we are doing this across all
engines? Is there a way we can isolate this a bit more?
Thanks,
Stuart
> +
> spin_lock_irqsave(&timelines->lock, flags);
> list_for_each_entry_safe(tl, tn, &timelines->active_list, link)
> {
> if (!mutex_trylock(&tl->mutex)) {
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