commit: 25ff1195f8a0b3724541ae7bbe331b4296de9c06 From: Chris Wilson <[email protected]> Date: Thu, 4 Apr 2013 21:31:03 +0100 Subject: drm/i915: Workaround incoherence between fences and LLC across multiple CPUs
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+, and manually flush writes to memory prior to writing the fence register in conjunction with the memory barriers placed around the register write. Fixes i-g-t/gem_fence_thrash v2: Bring a bigger gun v3: Switch the bigger gun for heavier bullets (Arjan van de Ven) v4: Remove changes for working generations. v5: Reduce to a per-cpu wbinvd() call prior to updating the fences. v6: Rewrite comments to ellide forgotten history. Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=62191 Signed-off-by: Chris Wilson <[email protected]> Cc: Jon Bloomfield <[email protected]> Tested-by: Jon Bloomfield <[email protected]> (v2) Cc: [email protected] Reviewed-by: Jesse Barnes <[email protected]> Signed-off-by: Daniel Vetter <[email protected]> --- drivers/gpu/drm/i915/i915_gem.c | 28 +++++++++++++++++++++++----- 1 file changed, 23 insertions(+), 5 deletions(-) diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c index 74c5601..63c05dd 100644 --- a/drivers/gpu/drm/i915/i915_gem.c +++ b/drivers/gpu/drm/i915/i915_gem.c @@ -2683,17 +2683,35 @@ static inline int fence_number(struct drm_i915_private *dev_priv, return fence - dev_priv->fence_regs; } +static void i915_gem_write_fence__ipi(void *data) +{ + wbinvd(); +} + 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; - int reg = fence_number(dev_priv, fence); - - i915_gem_write_fence(obj->base.dev, reg, enable ? obj : NULL); + struct drm_device *dev = obj->base.dev; + struct drm_i915_private *dev_priv = dev->dev_private; + int fence_reg = fence_number(dev_priv, fence); + + /* 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. + */ + if (HAS_LLC(obj->base.dev)) + on_each_cpu(i915_gem_write_fence__ipi, NULL, 1); + i915_gem_write_fence(dev, fence_reg, enable ? obj : NULL); if (enable) { - obj->fence_reg = reg; + obj->fence_reg = fence_reg; fence->obj = obj; list_move_tail(&fence->lru_list, &dev_priv->mm.fence_list); } else { -- 1.7.10.4 -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
