From 2def4ad99befa25775dd2f714fdd4d92faec6e34 Mon Sep 17 00:00:00 2001 From: Chris Wilson Date: Tue, 7 Apr 2015 16:20:41 +0100 Subject: [PATCH] drm/i915: Optimistically spin for the request completion This provides a nice boost to mesa in swap bound scenarios (as mesa throttles itself to the previous frame and given the scenario that will complete shortly). It will also provide a good boost to systems running with semaphores disabled and so frequently waiting on the GPU as it switches rings. In the most favourable of microbenchmarks, this can increase performance by around 15% - though in practice improvements will be marginal and rarely noticeable. v2: Account for user timeouts v3: Limit the spinning to a single jiffie (~1us) at most. On an otherwise idle system, there is no scheduler contention and so without a limit we would spin until the GPU is ready. v4: Drop forcewake - the lazy coherent access doesn't require it, and we have no reason to believe that the forcewake itself improves seqno coherency - it only adds delay. Signed-off-by: Chris Wilson Cc: Daniel Vetter Cc: Tvrtko Ursulin Cc: Eero Tamminen Cc: "Rantala, Valtteri" Reviewed-by: Tvrtko Ursulin Signed-off-by: Daniel Vetter --- drivers/gpu/drm/i915/i915_gem.c | 44 +++++++++++++++++++++++++++++++++++------ 1 file changed, 38 insertions(+), 6 deletions(-) diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c index 8ce363aa492c..b1c27da559e3 100644 --- a/drivers/gpu/drm/i915/i915_gem.c +++ b/drivers/gpu/drm/i915/i915_gem.c @@ -1181,6 +1181,29 @@ static bool missed_irq(struct drm_i915_private *dev_priv, return test_bit(ring->id, &dev_priv->gpu_error.missed_irq_rings); } +static int __i915_spin_request(struct drm_i915_gem_request *rq) +{ + unsigned long timeout; + + if (i915_gem_request_get_ring(rq)->irq_refcount) + return -EBUSY; + + timeout = jiffies + 1; + while (!need_resched()) { + if (i915_gem_request_completed(rq, true)) + return 0; + + if (time_after_eq(jiffies, timeout)) + break; + + cpu_relax_lowlatency(); + } + if (i915_gem_request_completed(rq, false)) + return 0; + + return -EAGAIN; +} + /** * __i915_wait_request - wait until execution of request has finished * @req: duh! @@ -1225,12 +1248,20 @@ int __i915_wait_request(struct drm_i915_gem_request *req, if (INTEL_INFO(dev)->gen >= 6) gen6_rps_boost(dev_priv, file_priv); - if (!irq_test_in_progress && WARN_ON(!ring->irq_get(ring))) - return -ENODEV; - /* Record current time in case interrupted by signal, or wedged */ trace_i915_gem_request_wait_begin(req); before = ktime_get_raw_ns(); + + /* Optimistic spin for the next jiffie before touching IRQs */ + ret = __i915_spin_request(req); + if (ret == 0) + goto out; + + if (!irq_test_in_progress && WARN_ON(!ring->irq_get(ring))) { + ret = -ENODEV; + goto out; + } + for (;;) { struct timer_list timer; @@ -1279,14 +1310,15 @@ int __i915_wait_request(struct drm_i915_gem_request *req, destroy_timer_on_stack(&timer); } } - now = ktime_get_raw_ns(); - trace_i915_gem_request_wait_end(req); - if (!irq_test_in_progress) ring->irq_put(ring); finish_wait(&ring->irq_queue, &wait); +out: + now = ktime_get_raw_ns(); + trace_i915_gem_request_wait_end(req); + if (timeout) { s64 tres = *timeout - (now - before); -- 2.11.0