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 <chris at chris-wilson.co.uk> Cc: Jon Bloomfield <jon.bloomfield at intel.com> Tested-by: Jon Bloomfield <jon.bloomfield at intel.com> (v2) Cc: stable at vger.kernel.org --- 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 fa4ea1a..8f7739e 100644 --- a/drivers/gpu/drm/i915/i915_gem.c +++ b/drivers/gpu/drm/i915/i915_gem.c @@ -2689,17 +2689,35 @@ 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
