From 26720ab97feac7153a7b5c3c79cf5d53a8531126 Mon Sep 17 00:00:00 2001 From: Tvrtko Ursulin Date: Thu, 17 Mar 2016 12:59:46 +0000 Subject: [PATCH] drm/i915: Move CSB MMIO reads out of the execlists lock By reading the CSB (slow MMIO accesses) into a temporary local buffer we can decrease the duration of holding the execlist lock. Main advantage is that during heavy batch buffer submission we reduce the execlist lock contention, which should decrease the latency and CPU usage between the submitting userspace process and interrupt handling. Downside is that we need to grab and relase the forcewake twice, but as the below numbers will show this is completely hidden by the primary gains. Testing with "gem_latency -n 100" (submit batch buffers with a hundred nops each) shows more than doubling of the throughput and more than halving of the dispatch latency, overall latency and CPU time spend in the submitting process. Submitting empty batches ("gem_latency -n 0") does not seem significantly affected by this change with throughput and CPU time improving by half a percent, and overall latency worsening by the same amount. Above tests were done in a hundred runs on a big core Broadwell. v2: * Overflow protection to local CSB buffer. * Use closer dev_priv in execlists_submit_requests. (Chris Wilson) v3: Rebase. v4: Added commend about irq needed to be disabled in execlists_submit_request. (Chris Wilson) Signed-off-by: Tvrtko Ursulin Cc: Chris Wilson Reviewed-by: Chris Wilsno Link: http://patchwork.freedesktop.org/patch/msgid/1458219586-20452-1-git-send-email-tvrtko.ursulin@linux.intel.com --- drivers/gpu/drm/i915/intel_lrc.c | 79 ++++++++++++++++++++-------------------- 1 file changed, 40 insertions(+), 39 deletions(-) diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c index 7c636b3..3a23b95 100644 --- a/drivers/gpu/drm/i915/intel_lrc.c +++ b/drivers/gpu/drm/i915/intel_lrc.c @@ -416,15 +416,25 @@ static void execlists_update_context(struct drm_i915_gem_request *rq) static void execlists_submit_requests(struct drm_i915_gem_request *rq0, struct drm_i915_gem_request *rq1) { + struct drm_i915_private *dev_priv = rq0->i915; + + /* BUG_ON(!irqs_disabled()); */ + execlists_update_context(rq0); if (rq1) execlists_update_context(rq1); + spin_lock(&dev_priv->uncore.lock); + intel_uncore_forcewake_get__locked(dev_priv, FORCEWAKE_ALL); + execlists_elsp_write(rq0, rq1); + + intel_uncore_forcewake_put__locked(dev_priv, FORCEWAKE_ALL); + spin_unlock(&dev_priv->uncore.lock); } -static void execlists_context_unqueue__locked(struct intel_engine_cs *engine) +static void execlists_context_unqueue(struct intel_engine_cs *engine) { struct drm_i915_gem_request *req0 = NULL, *req1 = NULL; struct drm_i915_gem_request *cursor, *tmp; @@ -478,19 +488,6 @@ static void execlists_context_unqueue__locked(struct intel_engine_cs *engine) execlists_submit_requests(req0, req1); } -static void execlists_context_unqueue(struct intel_engine_cs *engine) -{ - struct drm_i915_private *dev_priv = engine->dev->dev_private; - - spin_lock(&dev_priv->uncore.lock); - intel_uncore_forcewake_get__locked(dev_priv, FORCEWAKE_ALL); - - execlists_context_unqueue__locked(engine); - - intel_uncore_forcewake_put__locked(dev_priv, FORCEWAKE_ALL); - spin_unlock(&dev_priv->uncore.lock); -} - static unsigned int execlists_check_remove_request(struct intel_engine_cs *engine, u32 request_id) { @@ -551,12 +548,10 @@ void intel_lrc_irq_handler(struct intel_engine_cs *engine) struct drm_i915_private *dev_priv = engine->dev->dev_private; u32 status_pointer; unsigned int read_pointer, write_pointer; - u32 status = 0; - u32 status_id; + u32 csb[GEN8_CSB_ENTRIES][2]; + unsigned int csb_read = 0, i; unsigned int submit_contexts = 0; - spin_lock(&engine->execlist_lock); - spin_lock(&dev_priv->uncore.lock); intel_uncore_forcewake_get__locked(dev_priv, FORCEWAKE_ALL); @@ -568,41 +563,47 @@ void intel_lrc_irq_handler(struct intel_engine_cs *engine) write_pointer += GEN8_CSB_ENTRIES; while (read_pointer < write_pointer) { - status = get_context_status(engine, ++read_pointer, - &status_id); + if (WARN_ON_ONCE(csb_read == GEN8_CSB_ENTRIES)) + break; + csb[csb_read][0] = get_context_status(engine, ++read_pointer, + &csb[csb_read][1]); + csb_read++; + } - if (unlikely(status & GEN8_CTX_STATUS_PREEMPTED)) { - if (status & GEN8_CTX_STATUS_LITE_RESTORE) { - if (execlists_check_remove_request(engine, status_id)) + engine->next_context_status_buffer = write_pointer % GEN8_CSB_ENTRIES; + + /* Update the read pointer to the old write pointer. Manual ringbuffer + * management ftw */ + I915_WRITE_FW(RING_CONTEXT_STATUS_PTR(engine), + _MASKED_FIELD(GEN8_CSB_READ_PTR_MASK, + engine->next_context_status_buffer << 8)); + + intel_uncore_forcewake_put__locked(dev_priv, FORCEWAKE_ALL); + spin_unlock(&dev_priv->uncore.lock); + + spin_lock(&engine->execlist_lock); + + for (i = 0; i < csb_read; i++) { + if (unlikely(csb[i][0] & GEN8_CTX_STATUS_PREEMPTED)) { + if (csb[i][0] & GEN8_CTX_STATUS_LITE_RESTORE) { + if (execlists_check_remove_request(engine, csb[i][1])) WARN(1, "Lite Restored request removed from queue\n"); } else WARN(1, "Preemption without Lite Restore\n"); } - if (status & (GEN8_CTX_STATUS_ACTIVE_IDLE | + if (csb[i][0] & (GEN8_CTX_STATUS_ACTIVE_IDLE | GEN8_CTX_STATUS_ELEMENT_SWITCH)) submit_contexts += - execlists_check_remove_request(engine, - status_id); + execlists_check_remove_request(engine, csb[i][1]); } if (submit_contexts) { if (!engine->disable_lite_restore_wa || - (status & GEN8_CTX_STATUS_ACTIVE_IDLE)) - execlists_context_unqueue__locked(engine); + (csb[i][0] & GEN8_CTX_STATUS_ACTIVE_IDLE)) + execlists_context_unqueue(engine); } - engine->next_context_status_buffer = write_pointer % GEN8_CSB_ENTRIES; - - /* Update the read pointer to the old write pointer. Manual ringbuffer - * management ftw */ - I915_WRITE_FW(RING_CONTEXT_STATUS_PTR(engine), - _MASKED_FIELD(GEN8_CSB_READ_PTR_MASK, - engine->next_context_status_buffer << 8)); - - intel_uncore_forcewake_put__locked(dev_priv, FORCEWAKE_ALL); - spin_unlock(&dev_priv->uncore.lock); - spin_unlock(&engine->execlist_lock); if (unlikely(submit_contexts > 2)) -- 2.7.4