On Tue, Jul 09, 2013 at 05:54:40PM +0100, Chris Wilson wrote:
> This reverts commit 25ff119 and the follow on for Valleyview commit 2dc8aae.
>
> commit 25ff1195f8a0b3724541ae7bbe331b4296de9c06
> Author: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Date: Thu Apr 4 21:31:03 2013 +0100
>
> drm/i915: Workaround incoherence between fences and LLC across multiple CPUs
>
> commit 2dc8aae06d53458dd3624dc0accd4f81100ee631
> Author: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> 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 for the
> race condition, so lets run with it.
>
> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
> Cc: Jon Bloomfield <jon.bloomfield@xxxxxxxxx>
> Cc: Carsten Emde<C.Emde@xxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
Can you please add reference for the various bug reports we've gotten
from the realtime linux folks? Also we have some bug report from QA iirc
about a perf regression on UXA due to this.
-Daniel
> ---
> 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 ce46e777..96ede8c 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -2924,56 +2924,17 @@ 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 {
> --
> 1.8.3.2
>
--
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
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