Quoting Tvrtko Ursulin (2020-01-14 13:48:11) > > On 14/01/2020 11:20, Chris Wilson wrote: > > Quoting Tvrtko Ursulin (2020-01-14 11:13:06) > >> On 13/01/2020 10:44, Chris Wilson wrote: > >>> Since commit 422d7df4f090 ("drm/i915: Replace engine->timeline with a > >>> plain list"), we used the default embedded priotree slot for the virtual > >>> engine request queue, which means we can also use the same solitary slot > >>> with the scheduler. However, the priolist is expected to be guarded by > >>> the engine->active.lock, but this is not true for the virtual engine > >>> > >>> References: 422d7df4f090 ("drm/i915: Replace engine->timeline with a > >>> plain list") > >>> Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk> > >>> Cc: Mika Kuoppala <mika.kuopp...@linux.intel.com> > >>> Cc: Tvrtko Ursulin <tvrtko.ursu...@intel.com> > >>> --- > >>> drivers/gpu/drm/i915/gt/intel_lrc.c | 3 +++ > >>> drivers/gpu/drm/i915/i915_request.c | 4 +++- > >>> drivers/gpu/drm/i915/i915_request.h | 16 ++++++++++++++++ > >>> drivers/gpu/drm/i915/i915_scheduler.c | 3 +-- > >>> 4 files changed, 23 insertions(+), 3 deletions(-) > >>> > >>> diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c > >>> b/drivers/gpu/drm/i915/gt/intel_lrc.c > >>> index a6ac37dece0a..685659f079a2 100644 > >>> --- a/drivers/gpu/drm/i915/gt/intel_lrc.c > >>> +++ b/drivers/gpu/drm/i915/gt/intel_lrc.c > >>> @@ -985,6 +985,8 @@ __unwind_incomplete_requests(struct intel_engine_cs > >>> *engine) > >>> > >>> GEM_BUG_ON(RB_EMPTY_ROOT(&engine->execlists.queue.rb_root)); > >>> > >>> list_move(&rq->sched.link, pl); > >>> + set_bit(I915_FENCE_FLAG_PQUEUE, &rq->fence.flags); > >>> + > >>> active = rq; > >>> } else { > >>> struct intel_engine_cs *owner = > >>> rq->context->engine; > >>> @@ -2473,6 +2475,7 @@ static void execlists_submit_request(struct > >>> i915_request *request) > >>> spin_lock_irqsave(&engine->active.lock, flags); > >>> > >>> queue_request(engine, &request->sched, rq_prio(request)); > >>> + set_bit(I915_FENCE_FLAG_PQUEUE, &request->fence.flags); > >> > >> Move into queue_request so it is closer to priolist management, just like > >> at other call sites? > >> > >> Also, these are all under the engine active lock so non-atomic set/clear > >> could be used, no? > > > > It's not the bit that is important, but if there may be any other > > concurrent access to the dword. > > > > Thread A: Thread B: > > __set_bit(0, &rq->flags) __set_bit(31, &rq->flags) > > > > *does* cause an issue, speaking from sad experience. So if in doubt, and > > here there's always doubt with preempt-to-busy and background signaling, > > go atomic. > > > >> > >>> > >>> GEM_BUG_ON(RB_EMPTY_ROOT(&engine->execlists.queue.rb_root)); > >>> GEM_BUG_ON(list_empty(&request->sched.link)); > >>> diff --git a/drivers/gpu/drm/i915/i915_request.c > >>> b/drivers/gpu/drm/i915/i915_request.c > >>> index be185886e4fc..9ed0d3bc7249 100644 > >>> --- a/drivers/gpu/drm/i915/i915_request.c > >>> +++ b/drivers/gpu/drm/i915/i915_request.c > >>> @@ -408,8 +408,10 @@ bool __i915_request_submit(struct i915_request > >>> *request) > >>> xfer: /* We may be recursing from the signal callback of another > >>> i915 fence */ > >>> spin_lock_nested(&request->lock, SINGLE_DEPTH_NESTING); > >>> > >>> - if (!test_and_set_bit(I915_FENCE_FLAG_ACTIVE, > >>> &request->fence.flags)) > >>> + if (!test_and_set_bit(I915_FENCE_FLAG_ACTIVE, > >>> &request->fence.flags)) { > >>> list_move_tail(&request->sched.link, > >>> &engine->active.requests); > >>> + clear_bit(I915_FENCE_FLAG_PQUEUE, &request->fence.flags); > >>> + } > >>> > >>> if (test_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT, > >>> &request->fence.flags) && > >>> !test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &request->fence.flags) > >>> && > >>> diff --git a/drivers/gpu/drm/i915/i915_request.h > >>> b/drivers/gpu/drm/i915/i915_request.h > >>> index 031433691a06..f3e50ec989b8 100644 > >>> --- a/drivers/gpu/drm/i915/i915_request.h > >>> +++ b/drivers/gpu/drm/i915/i915_request.h > >>> @@ -70,6 +70,17 @@ enum { > >>> */ > >>> I915_FENCE_FLAG_ACTIVE = DMA_FENCE_FLAG_USER_BITS, > >>> > >>> + /* > >>> + * I915_FENCE_FLAG_PQUEUE - this request is ready for execution > >>> + * > >>> + * Using the scheduler, when a request is ready for execution it is > >>> put > >>> + * into the priority queue. We want to track its membership within > >>> that > >>> + * queue so that we can easily check before rescheduling. > >>> + * > >>> + * See i915_request_in_priority_queue() > >>> + */ > >>> + I915_FENCE_FLAG_PQUEUE, > >>> + > >>> /* > >>> * I915_FENCE_FLAG_SIGNAL - this request is currently on > >>> signal_list > >>> * > >>> @@ -361,6 +372,11 @@ static inline bool i915_request_is_active(const > >>> struct i915_request *rq) > >>> return test_bit(I915_FENCE_FLAG_ACTIVE, &rq->fence.flags); > >>> } > >>> > >>> +static inline bool i915_request_in_priority_queue(const struct > >>> i915_request *rq) > >>> +{ > >>> + return test_bit(I915_FENCE_FLAG_PQUEUE, &rq->fence.flags); > >>> +} > >>> + > >>> /** > >>> * Returns true if seq1 is later than seq2. > >>> */ > >>> diff --git a/drivers/gpu/drm/i915/i915_scheduler.c > >>> b/drivers/gpu/drm/i915/i915_scheduler.c > >>> index bf87c70bfdd9..4f6e4d6c590a 100644 > >>> --- a/drivers/gpu/drm/i915/i915_scheduler.c > >>> +++ b/drivers/gpu/drm/i915/i915_scheduler.c > >>> @@ -338,8 +338,7 @@ static void __i915_schedule(struct i915_sched_node > >>> *node, > >>> continue; > >>> } > >>> > >>> - if (!intel_engine_is_virtual(engine) && > >>> - !i915_request_is_active(node_to_request(node))) { > >>> + if (i915_request_in_priority_queue(node_to_request(node))) { > >> > >> Not shown in this diff before this if block we have: > >> > >> if (list_empty(&node->link)) { > >> /* > >> * If the request is not in the priolist queue because > >> * it is not yet runnable, then it doesn't contribute > >> * to our preemption decisions. On the other hand, > >> * if the request is on the HW, it too is not in the > >> * queue; but in that case we may still need to reorder > >> * the inflight requests. > > > > This second sentence is obsolete, we now use node->link for active. > > Which active? I915_FENCE_FLAG_ACTIVE is set when request is not on the > priority queue any more, no?
In the next patch, we introduce an inbetween state, ready but not active and not in the queue. > > > > >> */ > >> continue; > >> } > >> > >> What is the difference between list_empty(&node->link) and > >> !i915_request_in_priority_queue? > > > > list_empty() -> prior to being ready, we will put into the plist upon > > submit_request() > > > > Once ready, we only want to fiddle with its place in the priority lists, > > if it is in the plist. > > Yes brain fart on the list_empty check. > > However I need to go a step back and ask what is the whole point of this > block: > > if (!intel_engine_is_virtual(engine) && > !i915_request_is_active(node_to_request(node))) { > > For active request, they are already on the hw so no need to push them > up. But I forgot why are virtual ones special? VE is single context so > in order, or in other words no need to track prio levels for it, is that it? Yeah, it's because the lookup_prio didn't used work for virtual as it didn't have the tree. > But then also commit says "Use common priotree lists for virtual > engine". It already uses that before the patch because of the > !intel_engine_is_virtual condition. So I am confused. First iteration of this patch tweaked it so this block worked on virtual with no hassle. Then I realised I had a problem with on-hold requests, so took the patch a step further. -Chris _______________________________________________ Intel-gfx mailing list Intel-gfx@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/intel-gfx