Chris Wilson <ch...@chris-wilson.co.uk> writes:
> We dropped calling process_csb prior to handling direct submission in
> order to avoid the nesting of spinlocks and lift process_csb() and the
> majority of the tasklet out of irq-off. However, we do want to avoid
> ksoftirqd latency in the fast path, so try and pull the interrupt-bh
> local to direct submission if we can acquire the tasklet's lock.
>
> v2: Tweak the balance to avoid over submitting lite-restores
>
> Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk>
> Cc: Francisco Jerez <curroje...@riseup.net>
> Cc: Tvrtko Ursulin <tvrtko.ursu...@linux.intel.com>
> ---
> drivers/gpu/drm/i915/gt/intel_lrc.c | 44 ++++++++++++++++++++------
> drivers/gpu/drm/i915/gt/selftest_lrc.c | 2 +-
> 2 files changed, 36 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c
> b/drivers/gpu/drm/i915/gt/intel_lrc.c
> index f09dd87324b9..dceb65a0088f 100644
> --- a/drivers/gpu/drm/i915/gt/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
> @@ -2884,17 +2884,17 @@ static void queue_request(struct intel_engine_cs
> *engine,
> set_bit(I915_FENCE_FLAG_PQUEUE, &rq->fence.flags);
> }
>
> -static void __submit_queue_imm(struct intel_engine_cs *engine)
> +static bool pending_csb(const struct intel_engine_execlists *el)
> {
> - struct intel_engine_execlists * const execlists = &engine->execlists;
> + return READ_ONCE(*el->csb_write) != READ_ONCE(el->csb_head);
> +}
>
> - if (reset_in_progress(execlists))
> - return; /* defer until we restart the engine following reset */
> +static bool skip_lite_restore(struct intel_engine_execlists *el,
> + const struct i915_request *rq)
> +{
> + struct i915_request *inflight = execlists_active(el);
>
> - if (execlists->tasklet.func == execlists_submission_tasklet)
> - __execlists_submission_tasklet(engine);
> - else
> - tasklet_hi_schedule(&execlists->tasklet);
> + return inflight && inflight->context == rq->context;
> }
>
> static void submit_queue(struct intel_engine_cs *engine,
> @@ -2905,8 +2905,34 @@ static void submit_queue(struct intel_engine_cs
> *engine,
> if (rq_prio(rq) <= execlists->queue_priority_hint)
> return;
>
> + if (reset_in_progress(execlists))
> + return; /* defer until we restart the engine following reset */
> +
> + /*
> + * Suppress immediate lite-restores, leave that to the tasklet.
> + *
> + * However, we leave the queue_priority_hint unset so that if we do
> + * submit a second context, we push that into ELSP[1] immediately.
> + */
> + if (skip_lite_restore(execlists, rq))
> + return;
> +
Why do you need to treat lite-restore specially here?
Anyway, trying this out now in combination with my patches now.
> + /* Hopefully we clear execlists->pending[] to let us through */
> + if (execlists->pending[0] && tasklet_trylock(&execlists->tasklet)) {
> + process_csb(engine);
> + tasklet_unlock(&execlists->tasklet);
> + if (skip_lite_restore(execlists, rq))
> + return;
> + }
> +
> execlists->queue_priority_hint = rq_prio(rq);
> - __submit_queue_imm(engine);
> + __execlists_submission_tasklet(engine);
> +
> + /* Try and pull an interrupt-bh queued on another CPU to here */
> + if (pending_csb(execlists) && tasklet_trylock(&execlists->tasklet)) {
> + process_csb(engine);
> + tasklet_unlock(&execlists->tasklet);
> + }
> }
>
> static bool ancestor_on_hold(const struct intel_engine_cs *engine,
> diff --git a/drivers/gpu/drm/i915/gt/selftest_lrc.c
> b/drivers/gpu/drm/i915/gt/selftest_lrc.c
> index 6f06ba750a0a..c5c4b07a7d5f 100644
> --- a/drivers/gpu/drm/i915/gt/selftest_lrc.c
> +++ b/drivers/gpu/drm/i915/gt/selftest_lrc.c
> @@ -1028,7 +1028,7 @@ static int live_timeslice_rewind(void *arg)
> if (IS_ERR(rq[1]))
> goto err;
>
> - err = wait_for_submit(engine, rq[1], HZ / 2);
> + err = wait_for_submit(engine, rq[0], HZ / 2);
> if (err) {
> pr_err("%s: failed to submit first context\n",
> engine->name);
> --
> 2.20.1
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