From c0321e2c5acaaff7ed41d46d97cee71ad9238481 Mon Sep 17 00:00:00 2001 From: Chris Wilson Date: Mon, 26 Aug 2013 19:50:53 -0300 Subject: [PATCH] drm/i915: Do not add an interrupt for a context switch We use the request to ensure we hold a reference to the context for the duration that it remains in use by the ring. Each request only holds a reference to the current context, hence we emit a request after switching contexts with the final reference to the old context. However, the extra interrupt caused by that request is not useful (no timing critical function will wait for the context object), instead the overhead of servicing the IRQ shows up in some (lightweight) benchmarks. In order to keep the useful property of using the request to manage the context lifetime, we want to add a dummy request that is associated with the interrupt from the subsequent real request following the batch. The extra interrupt was added as a side-effect of using i915_add_request() in commit 112522f6789581824903f6f72082b5b841a7f0f9 Author: Chris Wilson Date: Thu May 2 16:48:07 2013 +0300 drm/i915: put context upon switching v2: Daniel convinced me that the request here was solely for context lifetime tracking and that we have the active ref to keep the object alive whilst the MI_SET_CONTEXT. So the only concern then is which context should get the blame for MI_SET_CONTEXT failing. The old scheme added a request for the old context so that any hang upto and including the switch away would mark the old context as guilty. Now any hang here implicates the new context. However since we have already gone through a complete flush with the last context in its last request, and all that lies in no-man's-land is an invalidate flush and the MI_SET_CONTEXT, we should be safe in not unduly placing blame on the new context. Signed-off-by: Chris Wilson Cc: Ben Widawsky Cc: Paulo Zanoni Reviewed-by: Damien Lespiau Signed-off-by: Daniel Vetter --- drivers/gpu/drm/i915/i915_gem.c | 1 - drivers/gpu/drm/i915/i915_gem_context.c | 12 +----------- 2 files changed, 1 insertion(+), 12 deletions(-) diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c index 80342c8..22be39f 100644 --- a/drivers/gpu/drm/i915/i915_gem.c +++ b/drivers/gpu/drm/i915/i915_gem.c @@ -2045,7 +2045,6 @@ int __i915_add_request(struct intel_ring_buffer *ring, if (request == NULL) return -ENOMEM; - /* Record the position of the start of the request so that * should we detect the updated seqno part-way through the * GPU processing the request, we never over-estimate the diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c index 403309c..b6da70b 100644 --- a/drivers/gpu/drm/i915/i915_gem_context.c +++ b/drivers/gpu/drm/i915/i915_gem_context.c @@ -451,17 +451,7 @@ static int do_switch(struct i915_hw_context *to) from->obj->dirty = 1; BUG_ON(from->obj->ring != ring); - ret = i915_add_request(ring, NULL); - if (ret) { - /* Too late, we've already scheduled a context switch. - * Try to undo the change so that the hw state is - * consistent with out tracking. In case of emergency, - * scream. - */ - WARN_ON(mi_set_context(ring, from, MI_RESTORE_INHIBIT)); - return ret; - } - + /* obj is kept alive until the next request by its active ref */ i915_gem_object_unpin(from->obj); i915_gem_context_unreference(from); } -- 2.7.4