From 3d5564e91025bd17d93d0a23ebf8e22309652591 Mon Sep 17 00:00:00 2001 From: Chris Wilson Date: Fri, 1 Jul 2016 17:23:23 +0100 Subject: [PATCH] drm/i915: Only apply one barrier after a breadcrumb interrupt is posted If we flag the seqno as potentially stale upon receiving an interrupt, we can use that information to reduce the frequency that we apply the heavyweight coherent seqno read (i.e. if we wake up a chain of waiters). v2: Use cmpxchg to replace READ_ONCE/WRITE_ONCE for more explicit control of the ordering wrt to interrupt generation and interrupt checking in the bottom-half. Signed-off-by: Chris Wilson Reviewed-by: Tvrtko Ursulin Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-14-git-send-email-chris@chris-wilson.co.uk --- drivers/gpu/drm/i915/i915_drv.h | 15 ++++++++++++++- drivers/gpu/drm/i915/i915_irq.c | 1 + drivers/gpu/drm/i915/intel_breadcrumbs.c | 16 ++++++++++------ drivers/gpu/drm/i915/intel_ringbuffer.h | 1 + 4 files changed, 26 insertions(+), 7 deletions(-) diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h index ee04bd40a41a..21181a6ec0b0 100644 --- a/drivers/gpu/drm/i915/i915_drv.h +++ b/drivers/gpu/drm/i915/i915_drv.h @@ -4005,7 +4005,20 @@ static inline bool __i915_request_irq_complete(struct drm_i915_gem_request *req) * but it is easier and safer to do it every time the waiter * is woken. */ - if (engine->irq_seqno_barrier) { + if (engine->irq_seqno_barrier && + cmpxchg_relaxed(&engine->irq_posted, 1, 0)) { + /* The ordering of irq_posted versus applying the barrier + * is crucial. The clearing of the current irq_posted must + * be visible before we perform the barrier operation, + * such that if a subsequent interrupt arrives, irq_posted + * is reasserted and our task rewoken (which causes us to + * do another __i915_request_irq_complete() immediately + * and reapply the barrier). Conversely, if the clear + * occurs after the barrier, then an interrupt that arrived + * whilst we waited on the barrier would not trigger a + * barrier on the next pass, and the read may not see the + * seqno update. + */ engine->irq_seqno_barrier(engine); if (i915_gem_request_completed(req)) return true; diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c index be7f0b9b27e0..7724bae27bcf 100644 --- a/drivers/gpu/drm/i915/i915_irq.c +++ b/drivers/gpu/drm/i915/i915_irq.c @@ -976,6 +976,7 @@ static void ironlake_rps_change_irq_handler(struct drm_i915_private *dev_priv) static void notify_ring(struct intel_engine_cs *engine) { + smp_store_mb(engine->irq_posted, true); if (intel_engine_wakeup(engine)) { trace_i915_gem_request_notify(engine); engine->user_interrupts++; diff --git a/drivers/gpu/drm/i915/intel_breadcrumbs.c b/drivers/gpu/drm/i915/intel_breadcrumbs.c index 7cdb02d18c1f..85ef6c0e2913 100644 --- a/drivers/gpu/drm/i915/intel_breadcrumbs.c +++ b/drivers/gpu/drm/i915/intel_breadcrumbs.c @@ -43,12 +43,18 @@ static void intel_breadcrumbs_fake_irq(unsigned long data) static void irq_enable(struct intel_engine_cs *engine) { + /* Enabling the IRQ may miss the generation of the interrupt, but + * we still need to force the barrier before reading the seqno, + * just in case. + */ + engine->irq_posted = true; WARN_ON(!engine->irq_get(engine)); } static void irq_disable(struct intel_engine_cs *engine) { engine->irq_put(engine); + engine->irq_posted = false; } static bool __intel_breadcrumbs_enable_irq(struct intel_breadcrumbs *b) @@ -56,7 +62,6 @@ static bool __intel_breadcrumbs_enable_irq(struct intel_breadcrumbs *b) struct intel_engine_cs *engine = container_of(b, struct intel_engine_cs, breadcrumbs); struct drm_i915_private *i915 = engine->i915; - bool irq_posted = false; assert_spin_locked(&b->lock); if (b->rpm_wakelock) @@ -72,10 +77,8 @@ static bool __intel_breadcrumbs_enable_irq(struct intel_breadcrumbs *b) /* No interrupts? Kick the waiter every jiffie! */ if (intel_irqs_enabled(i915)) { - if (!test_bit(engine->id, &i915->gpu_error.test_irq_rings)) { + if (!test_bit(engine->id, &i915->gpu_error.test_irq_rings)) irq_enable(engine); - irq_posted = true; - } b->irq_enabled = true; } @@ -83,7 +86,7 @@ static bool __intel_breadcrumbs_enable_irq(struct intel_breadcrumbs *b) test_bit(engine->id, &i915->gpu_error.missed_irq_rings)) mod_timer(&b->fake_irq, jiffies + 1); - return irq_posted; + return engine->irq_posted; } static void __intel_breadcrumbs_disable_irq(struct intel_breadcrumbs *b) @@ -207,7 +210,8 @@ static bool __intel_engine_add_wait(struct intel_engine_cs *engine, * in case the seqno passed. */ __intel_breadcrumbs_enable_irq(b); - wake_up_process(to_wait(next)->tsk); + if (READ_ONCE(engine->irq_posted)) + wake_up_process(to_wait(next)->tsk); } do { diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h index ad86686e57f0..fcc348376080 100644 --- a/drivers/gpu/drm/i915/intel_ringbuffer.h +++ b/drivers/gpu/drm/i915/intel_ringbuffer.h @@ -185,6 +185,7 @@ struct intel_engine_cs { struct i915_ctx_workarounds wa_ctx; unsigned irq_refcount; /* protected by dev_priv->irq_lock */ + bool irq_posted; u32 irq_enable_mask; /* bitmask to enable ring interrupt */ struct drm_i915_gem_request *trace_irq_req; bool __must_check (*irq_get)(struct intel_engine_cs *ring); -- GitLab