From 44d89409a12eb8333735958509d7d591b461d13d Mon Sep 17 00:00:00 2001 From: Chris Wilson Date: Tue, 18 Jun 2019 08:41:35 +0100 Subject: [PATCH] drm/i915: Make the semaphore saturation mask global The idea behind keeping the saturation mask local to a context backfired spectacularly. The premise with the local mask was that we would be more proactive in attempting to use semaphores after each time the context idled, and that all new contexts would attempt to use semaphores ignoring the current state of the system. This turns out to be horribly optimistic. If the system state is still oversaturated and the existing workloads have all stopped using semaphores, the new workloads would attempt to use semaphores and be deprioritised behind real work. The new contexts would not switch off using semaphores until their initial batch of low priority work had completed. Given sufficient backload load of equal user priority, this would completely starve the new work of any GPU time. To compensate, remove the local tracking in favour of keeping it as global state on the engine -- once the system is saturated and semaphores are disabled, everyone stops attempting to use semaphores until the system is idle again. One of the reason for preferring local context tracking was that it worked with virtual engines, so for switching to global state we could either do a complete check of all the virtual siblings or simply disable semaphores for those requests. This takes the simpler approach of disabling semaphores on virtual engines. The downside is that the decision that the engine is saturated is a local measure -- we are only checking whether or not this context was scheduled in a timely fashion, it may be legitimately delayed due to user priorities. We still have the same dilemma though, that we do not want to employ the semaphore poll unless it will be used. v2: Explain why we need to assume the worst wrt virtual engines. Fixes: ca6e56f654e7 ("drm/i915: Disable semaphore busywaits on saturated systems") Signed-off-by: Chris Wilson Cc: Tvrtko Ursulin Cc: Dmitry Rogozhkin Cc: Dmitry Ermilov Reviewed-by: Tvrtko Ursulin Link: https://patchwork.freedesktop.org/patch/msgid/20190618074153.16055-8-chris@chris-wilson.co.uk --- drivers/gpu/drm/i915/gt/intel_context.c | 2 -- drivers/gpu/drm/i915/gt/intel_context_types.h | 2 -- drivers/gpu/drm/i915/gt/intel_engine_pm.c | 2 ++ drivers/gpu/drm/i915/gt/intel_engine_types.h | 2 ++ drivers/gpu/drm/i915/gt/intel_lrc.c | 16 +++++++++++++++- drivers/gpu/drm/i915/i915_request.c | 4 ++-- 6 files changed, 21 insertions(+), 7 deletions(-) diff --git a/drivers/gpu/drm/i915/gt/intel_context.c b/drivers/gpu/drm/i915/gt/intel_context.c index 42f45744d859..2c454f227c2e 100644 --- a/drivers/gpu/drm/i915/gt/intel_context.c +++ b/drivers/gpu/drm/i915/gt/intel_context.c @@ -142,7 +142,6 @@ intel_context_init(struct intel_context *ce, ce->engine = engine; ce->ops = engine->cops; ce->sseu = engine->sseu; - ce->saturated = 0; INIT_LIST_HEAD(&ce->signal_link); INIT_LIST_HEAD(&ce->signals); @@ -223,7 +222,6 @@ void intel_context_enter_engine(struct intel_context *ce) void intel_context_exit_engine(struct intel_context *ce) { - ce->saturated = 0; intel_engine_pm_put(ce->engine); } diff --git a/drivers/gpu/drm/i915/gt/intel_context_types.h b/drivers/gpu/drm/i915/gt/intel_context_types.h index e95be4be9612..08049ee91cee 100644 --- a/drivers/gpu/drm/i915/gt/intel_context_types.h +++ b/drivers/gpu/drm/i915/gt/intel_context_types.h @@ -53,8 +53,6 @@ struct intel_context { atomic_t pin_count; struct mutex pin_mutex; /* guards pinning and associated on-gpuing */ - intel_engine_mask_t saturated; /* submitting semaphores too late? */ - /** * active: Active tracker for the rq activity (inc. external) on this * intel_context object. diff --git a/drivers/gpu/drm/i915/gt/intel_engine_pm.c b/drivers/gpu/drm/i915/gt/intel_engine_pm.c index d14e352b0b17..2ce00d3dc42a 100644 --- a/drivers/gpu/drm/i915/gt/intel_engine_pm.c +++ b/drivers/gpu/drm/i915/gt/intel_engine_pm.c @@ -100,6 +100,8 @@ static int __engine_park(struct intel_wakeref *wf) struct intel_engine_cs *engine = container_of(wf, typeof(*engine), wakeref); + engine->saturated = 0; + /* * If one and only one request is completed between pm events, * we know that we are inside the kernel context and it is diff --git a/drivers/gpu/drm/i915/gt/intel_engine_types.h b/drivers/gpu/drm/i915/gt/intel_engine_types.h index b2faca8e5dec..868b220214f8 100644 --- a/drivers/gpu/drm/i915/gt/intel_engine_types.h +++ b/drivers/gpu/drm/i915/gt/intel_engine_types.h @@ -298,6 +298,8 @@ struct intel_engine_cs { struct intel_context *kernel_context; /* pinned */ struct intel_context *preempt_context; /* pinned; optional */ + intel_engine_mask_t saturated; /* submitting semaphores too late? */ + unsigned long serial; unsigned long wakeref_serial; diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c index c400c66d0ee5..df58d1d838f7 100644 --- a/drivers/gpu/drm/i915/gt/intel_lrc.c +++ b/drivers/gpu/drm/i915/gt/intel_lrc.c @@ -3102,7 +3102,6 @@ static void virtual_context_exit(struct intel_context *ce) struct virtual_engine *ve = container_of(ce, typeof(*ve), context); unsigned int n; - ce->saturated = 0; for (n = 0; n < ve->num_siblings; n++) intel_engine_pm_put(ve->siblings[n]); } @@ -3302,6 +3301,21 @@ intel_execlists_create_virtual(struct i915_gem_context *ctx, ve->base.instance = I915_ENGINE_CLASS_INVALID_VIRTUAL; ve->base.flags = I915_ENGINE_IS_VIRTUAL; + /* + * The decision on whether to submit a request using semaphores + * depends on the saturated state of the engine. We only compute + * this during HW submission of the request, and we need for this + * state to be globally applied to all requests being submitted + * to this engine. Virtual engines encompass more than one physical + * engine and so we cannot accurately tell in advance if one of those + * engines is already saturated and so cannot afford to use a semaphore + * and be pessimized in priority for doing so -- if we are the only + * context using semaphores after all other clients have stopped, we + * will be starved on the saturated system. Such a global switch for + * semaphores is less than ideal, but alas is the current compromise. + */ + ve->base.saturated = ALL_ENGINES; + snprintf(ve->base.name, sizeof(ve->base.name), "virtual"); intel_engine_init_active(&ve->base, ENGINE_VIRTUAL); diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c index 7418e8f1ed6a..0c2b53b8a3d1 100644 --- a/drivers/gpu/drm/i915/i915_request.c +++ b/drivers/gpu/drm/i915/i915_request.c @@ -407,7 +407,7 @@ void __i915_request_submit(struct i915_request *request) */ if (request->sched.semaphores && i915_sw_fence_signaled(&request->semaphore)) - request->hw_context->saturated |= request->sched.semaphores; + engine->saturated |= request->sched.semaphores; /* We may be recursing from the signal callback of another i915 fence */ spin_lock_nested(&request->lock, SINGLE_DEPTH_NESTING); @@ -787,7 +787,7 @@ already_busywaiting(struct i915_request *rq) * * See the are-we-too-late? check in __i915_request_submit(). */ - return rq->sched.semaphores | rq->hw_context->saturated; + return rq->sched.semaphores | rq->engine->saturated; } static int -- 2.30.2