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drm/i915: Disable use of hwsp_cacheline for kernel_context

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Currently on execlists, we use a local hwsp for the kernel_context,
rather than the engine's HWSP, as this is the default for execlists.
However, seqno wrap requires allocating a new HWSP cacheline, and may
require pinning a new HWSP page in the GGTT. This operation requiring
pinning in the GGTT is not allowed within the kernel_context timeline,
as doing so may require re-entering the kernel_context in order to evict
from the GGTT. As we want to avoid requiring a new HWSP for the
kernel_context, we can use the permanently pinned engine's HWSP instead.
However to do so we must prevent the use of semaphores reading the
kernel_context's HWSP, as the use of semaphores do not support rollover
onto the same cacheline. Fortunately, the kernel_context is mostly
isolated, so unlikely to give benefit to semaphores.

Reported-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200210205722.794180-5-chris@chris-wilson.co.uk
This commit is contained in:
Chris Wilson
2020-02-10 20:57:20 +00:00
parent 6313e78e72
commit f16ccb6445
3 changed files with 30 additions and 10 deletions
Download Patch File Download Diff File Expand all files Collapse all files

14
drivers/gpu/drm/i915/i915_request.c
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@@ -886,6 +886,12 @@ emit_semaphore_wait(struct i915_request *to,
struct i915_request *from,
gfp_t gfp)
{
if (!intel_context_use_semaphores(to->context))
goto await_fence;
if (!rcu_access_pointer(from->hwsp_cacheline))
goto await_fence;
/* Just emit the first semaphore we see as request space is limited. */
if (already_busywaiting(to) & from->engine->mask)
goto await_fence;
@@ -931,12 +937,8 @@ i915_request_await_request(struct i915_request *to, struct i915_request *from)
ret = i915_sw_fence_await_sw_fence_gfp(&to->submit,
&from->submit,
I915_FENCE_GFP);
else if (intel_context_use_semaphores(to->context))
ret = emit_semaphore_wait(to, from, I915_FENCE_GFP);
else
ret = i915_sw_fence_await_dma_fence(&to->submit,
&from->fence, 0,
I915_FENCE_GFP);
ret = emit_semaphore_wait(to, from, I915_FENCE_GFP);
if (ret < 0)
return ret;
@@ -1035,6 +1037,8 @@ __i915_request_await_execution(struct i915_request *to,
{
int err;
GEM_BUG_ON(intel_context_is_barrier(from->context));
/* Submit both requests at the same time */
err = __await_execution(to, from, hook, I915_FENCE_GFP);
if (err)