> -----Original Message-----
> From: Intel-gfx <intel-gfx-bounces@xxxxxxxxxxxxxxxxxxxxx> On Behalf Of Chris
> Wilson
> Sent: Tuesday, June 16, 2020 12:02 PM
> To: intel-gfx@xxxxxxxxxxxxxxxxxxxxx
> Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Subject: [PATCH] drm/i915/gt: Decouple completed requests on
> unwind
>
> Since the introduction of preempt-to-busy, requests can complete in the
> background, even while they are not on the engine->active.requests list.
> As such, the engine->active.request list itself is not in strict retirement order,
> and we have to scan the entire list while unwinding to not miss any.
> However, if the request is completed we currently leave it on the list [until
> retirement], but we could just as simply remove it and stop treating it as
> active. We would only have to then traverse it once while unwinding in quick
> succession.
>
> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> ---
> drivers/gpu/drm/i915/gt/intel_lrc.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c
> b/drivers/gpu/drm/i915/gt/intel_lrc.c
> index e866b8d721ed..4eb397b0e14d 100644
> --- a/drivers/gpu/drm/i915/gt/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
> @@ -1114,8 +1114,10 @@ __unwind_incomplete_requests(struct
> intel_engine_cs *engine)
> list_for_each_entry_safe_reverse(rq, rn,
> &engine->active.requests,
> sched.link) {
> - if (i915_request_completed(rq))
> - continue; /* XXX */
> + if (i915_request_completed(rq)) {
> + list_del_init(&rq->sched.link);
Albeit this seems like a valid approach to resolve inconsistence in the list of requests that are active or retired, but we can't just delete completed requests from the list until full retirement is done - otherwise we stand the risk of out-of-the-order list, and could lead to inconsistence (which is the original problem you intend to resolve). Have you thought about locking mechanism?
Regards,
~Akeem
> + continue;
> + }
>
> __i915_request_unsubmit(rq);
>
> --
> 2.20.1
>
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