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drm/i915: Workaround incoherence between fences and LLC across multiple CPUs

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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@chris-wilson.co.uk>
Cc: Jon Bloomfield <jon.bloomfield@intel.com>
Tested-by: Jon Bloomfield <jon.bloomfield@intel.com> (v2)
Cc: stable@vger.kernel.org
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
This commit is contained in:
Chris Wilson 2013-04-04 21:31:03 +01:00 committed by Daniel Vetter
parent 8bb6e9590b
commit 25ff1195f8
1 changed files with 22 additions and 4 deletions
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26
drivers/gpu/drm/i915/i915_gem.c
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@ -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);
struct drm_device *dev = obj->base.dev;
struct drm_i915_private *dev_priv = dev->dev_private;
int fence_reg = fence_number(dev_priv, fence);
i915_gem_write_fence(obj->base.dev, reg, 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.
*/
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 {