From f9e9e9de58c7b7bb8344128d6de2c79b87a7fabf Mon Sep 17 00:00:00 2001 From: Chris Wilson Date: Fri, 1 Mar 2019 17:09:01 +0000 Subject: [PATCH] drm/i915: Prioritise non-busywait semaphore workloads We don't want to busywait on the GPU if we have other work to do. If we give non-busywaiting workloads higher (initial) priority than workloads that require a busywait, we will prioritise work that is ready to run immediately. We then also have to be careful that we don't give earlier semaphores an accidental boost because later work doesn't wait on other rings, hence we keep a history of semaphore usage of the dependency chain. v2: Stop rolling the bits into a chain and just use a flag in case this request or any of our dependencies use a semaphore. The rolling around was contagious as Tvrtko was heard to fall off his chair. Testcase: igt/gem_exec_schedule/semaphore Signed-off-by: Chris Wilson Cc: Tvrtko Ursulin Reviewed-by: Tvrtko Ursulin Link: https://patchwork.freedesktop.org/patch/msgid/20190301170901.8340-4-chris@chris-wilson.co.uk --- drivers/gpu/drm/i915/i915_request.c | 16 ++++++++++++++++ drivers/gpu/drm/i915/i915_scheduler.c | 6 ++++++ drivers/gpu/drm/i915/i915_scheduler.h | 9 ++++++--- drivers/gpu/drm/i915/intel_lrc.c | 2 +- 4 files changed, 29 insertions(+), 4 deletions(-) diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c index 59e30b8c4ee9..bcf3c1a155e2 100644 --- a/drivers/gpu/drm/i915/i915_request.c +++ b/drivers/gpu/drm/i915/i915_request.c @@ -813,6 +813,7 @@ emit_semaphore_wait(struct i915_request *to, *cs++ = 0; intel_ring_advance(to, cs); + to->sched.flags |= I915_SCHED_HAS_SEMAPHORE; return 0; } @@ -1083,6 +1084,21 @@ void i915_request_add(struct i915_request *request) if (engine->schedule) { struct i915_sched_attr attr = request->gem_context->sched; + /* + * Boost actual workloads past semaphores! + * + * With semaphores we spin on one engine waiting for another, + * simply to reduce the latency of starting our work when + * the signaler completes. However, if there is any other + * work that we could be doing on this engine instead, that + * is better utilisation and will reduce the overall duration + * of the current work. To avoid PI boosting a semaphore + * far in the distance past over useful work, we keep a history + * of any semaphore use along our dependency chain. + */ + if (!(request->sched.flags & I915_SCHED_HAS_SEMAPHORE)) + attr.priority |= I915_PRIORITY_NOSEMAPHORE; + /* * Boost priorities to new clients (new request flows). * diff --git a/drivers/gpu/drm/i915/i915_scheduler.c b/drivers/gpu/drm/i915/i915_scheduler.c index 50018ad30233..3f0a4d56bd37 100644 --- a/drivers/gpu/drm/i915/i915_scheduler.c +++ b/drivers/gpu/drm/i915/i915_scheduler.c @@ -39,6 +39,7 @@ void i915_sched_node_init(struct i915_sched_node *node) INIT_LIST_HEAD(&node->waiters_list); INIT_LIST_HEAD(&node->link); node->attr.priority = I915_PRIORITY_INVALID; + node->flags = 0; } static struct i915_dependency * @@ -69,6 +70,11 @@ bool __i915_sched_node_add_dependency(struct i915_sched_node *node, dep->signaler = signal; dep->flags = flags; + /* Keep track of whether anyone on this chain has a semaphore */ + if (signal->flags & I915_SCHED_HAS_SEMAPHORE && + !node_started(signal)) + node->flags |= I915_SCHED_HAS_SEMAPHORE; + ret = true; } diff --git a/drivers/gpu/drm/i915/i915_scheduler.h b/drivers/gpu/drm/i915/i915_scheduler.h index 7d4a49750d92..6ce450cf63fa 100644 --- a/drivers/gpu/drm/i915/i915_scheduler.h +++ b/drivers/gpu/drm/i915/i915_scheduler.h @@ -24,14 +24,15 @@ enum { I915_PRIORITY_INVALID = INT_MIN }; -#define I915_USER_PRIORITY_SHIFT 2 +#define I915_USER_PRIORITY_SHIFT 3 #define I915_USER_PRIORITY(x) ((x) << I915_USER_PRIORITY_SHIFT) #define I915_PRIORITY_COUNT BIT(I915_USER_PRIORITY_SHIFT) #define I915_PRIORITY_MASK (I915_PRIORITY_COUNT - 1) -#define I915_PRIORITY_WAIT ((u8)BIT(0)) -#define I915_PRIORITY_NEWCLIENT ((u8)BIT(1)) +#define I915_PRIORITY_WAIT ((u8)BIT(0)) +#define I915_PRIORITY_NEWCLIENT ((u8)BIT(1)) +#define I915_PRIORITY_NOSEMAPHORE ((u8)BIT(2)) #define __NO_PREEMPTION (I915_PRIORITY_WAIT) @@ -74,6 +75,8 @@ struct i915_sched_node { struct list_head waiters_list; /* those after us, they depend upon us */ struct list_head link; struct i915_sched_attr attr; + unsigned int flags; +#define I915_SCHED_HAS_SEMAPHORE BIT(0) }; struct i915_dependency { diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c index 6c9479acb433..578c8c98c718 100644 --- a/drivers/gpu/drm/i915/intel_lrc.c +++ b/drivers/gpu/drm/i915/intel_lrc.c @@ -164,7 +164,7 @@ #define WA_TAIL_DWORDS 2 #define WA_TAIL_BYTES (sizeof(u32) * WA_TAIL_DWORDS) -#define ACTIVE_PRIORITY (I915_PRIORITY_NEWCLIENT) +#define ACTIVE_PRIORITY (I915_PRIORITY_NEWCLIENT | I915_PRIORITY_NOSEMAPHORE) static int execlists_context_deferred_alloc(struct i915_gem_context *ctx, struct intel_engine_cs *engine, -- 2.30.2