Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> writes:
> If an interrupt has been posted, and we were spinning on the active
> seqno waiting for it to advance but it did not, then we can expect that
> it will not see its advance in the immediate future and should call into
> the irq-seqno barrier. We can stop spinning at this point, and leave the
> difficulty of handling the coherency to the caller.
>
> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
> Cc: Mika Kuoppala <mika.kuoppala@xxxxxxxxxxxxxxx>
> ---
> drivers/gpu/drm/i915/i915_gem_request.c | 15 ++++++++++++---
> 1 file changed, 12 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_gem_request.c b/drivers/gpu/drm/i915/i915_gem_request.c
> index 7760d7481f85..de52ac18e215 100644
> --- a/drivers/gpu/drm/i915/i915_gem_request.c
> +++ b/drivers/gpu/drm/i915/i915_gem_request.c
> @@ -972,7 +972,8 @@ static bool busywait_stop(unsigned long timeout, unsigned int cpu)
> bool __i915_spin_request(const struct drm_i915_gem_request *req,
> u32 seqno, int state, unsigned long timeout_us)
> {
> - unsigned int cpu;
> + struct intel_engine_cs *engine = req->engine;
> + unsigned int irq, cpu;
>
> /* When waiting for high frequency requests, e.g. during synchronous
> * rendering split between the CPU and GPU, the finite amount of time
> @@ -984,15 +985,23 @@ bool __i915_spin_request(const struct drm_i915_gem_request *req,
> * takes to sleep on a request, on the order of a microsecond.
> */
>
> + irq = atomic_read(&engine->irq_count);
> timeout_us += local_clock_us(&cpu);
> do {
> if (seqno != i915_gem_request_global_seqno(req))
> break;
>
> - if (i915_seqno_passed(intel_engine_get_seqno(req->engine),
> - seqno))
> + if (i915_seqno_passed(intel_engine_get_seqno(engine), seqno))
> return true;
>
> + /* Seqno are meant to be ordered *before* the interrupt. If
> + * we see an interrupt without a corresponding seqno advance,
> + * assume we won't see one in the near future but require
> + * the engine->seqno_barrier() to fixup coherency.
> + */
> + if (atomic_read(&engine->irq_count) != irq)
> + break;
> +
Looks good but now need to wait for patch to introduce
irq_counts to materialize.
-Mika
> if (signal_pending_state(state, current))
> break;
>
> --
> 2.11.0
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