From 4627ebffeb0b5d0ffdc8fbf1452885f07bf21bfd Mon Sep 17 00:00:00 2001 From: Chris Wilson Date: Wed, 10 Jul 2013 13:36:24 +0100 Subject: [PATCH] Revert "drm/i915: Workaround incoherence between fences and LLC across multiple CPUs" This reverts commit 4d81516 and the follow on for Valleyview commit b61e62a. commit 4d8151650eb04c3451e998eee5aaac1fad538965 Author: Chris Wilson Date: Thu Apr 4 21:31:03 2013 +0100 drm/i915: Workaround incoherence between fences and LLC across multiple CPUs commit b61e62ae65a2089a9dd8d03b570c1f6893401cfc Author: Chris Wilson Date: Wed May 22 17:08:06 2013 +0100 drm/i915: Workaround incoherence with fence updates on Valleyview Jon Bloomfield came up with a plausible explanation and cheap fix (drm/i915: Fix incoherence with fence updates on Sandybridge+) for the race condition, so lets run with it. This is a candidate for stable as the old workaround incurs a significant cost (calling wbinvd on all CPUs before performing the register write) for some workloads as noted by Carsten Emde. Link: http://lists.freedesktop.org/archives/intel-gfx/2013-June/028819.html References: https://www.osadl.org/?id=1543#c7602 References: https://bugs.freedesktop.org/show_bug.cgi?id=63825 Signed-off-by: Chris Wilson Cc: Daniel Vetter Cc: Jon Bloomfield Cc: Carsten Emde Cc: stable@vger.kernel.org Signed-off-by: Daniel Vetter --- drivers/gpu/drm/i915/i915_gem.c | 47 +++------------------------------ 1 file changed, 4 insertions(+), 43 deletions(-) diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c index a34e8e2ba98a2..06d66e09da172 100644 --- a/drivers/gpu/drm/i915/i915_gem.c +++ b/drivers/gpu/drm/i915/i915_gem.c @@ -2829,56 +2829,17 @@ static inline int fence_number(struct drm_i915_private *dev_priv, return fence - dev_priv->fence_regs; } -struct write_fence { - struct drm_device *dev; - struct drm_i915_gem_object *obj; - int fence; -}; - -static void i915_gem_write_fence__ipi(void *data) -{ - struct write_fence *args = data; - - /* Required for SNB+ with LLC */ - wbinvd(); - - /* Required for VLV */ - i915_gem_write_fence(args->dev, args->fence, args->obj); -} - static void i915_gem_object_update_fence(struct drm_i915_gem_object *obj, struct drm_i915_fence_reg *fence, bool enable) { struct drm_i915_private *dev_priv = obj->base.dev->dev_private; - struct write_fence args = { - .dev = obj->base.dev, - .fence = fence_number(dev_priv, fence), - .obj = enable ? obj : NULL, - }; - - /* In order to fully serialize access to the fenced region and - * the update to the fence register we need to take extreme - * measures on SNB+. In theory, the write to the fence register - * flushes all memory transactions before, and coupled with the - * mb() placed around the register write we serialise all memory - * operations with respect to the changes in the tiler. Yet, on - * SNB+ we need to take a step further and emit an explicit wbinvd() - * on each processor in order to manually flush all memory - * transactions before updating the fence register. - * - * However, Valleyview complicates matter. There the wbinvd is - * insufficient and unlike SNB/IVB requires the serialising - * register write. (Note that that register write by itself is - * conversely not sufficient for SNB+.) To compromise, we do both. - */ - if (INTEL_INFO(args.dev)->gen >= 6) - on_each_cpu(i915_gem_write_fence__ipi, &args, 1); - else - i915_gem_write_fence(args.dev, args.fence, args.obj); + int reg = fence_number(dev_priv, fence); + + i915_gem_write_fence(obj->base.dev, reg, enable ? obj : NULL); if (enable) { - obj->fence_reg = args.fence; + obj->fence_reg = reg; fence->obj = obj; list_move_tail(&fence->lru_list, &dev_priv->mm.fence_list); } else { -- 2.39.5