[Intel-gfx] [PATCH] RFC drm/i915: Slaughter the thundering i915_wait_request herd

[Chris Wilson]

On Mon, Nov 02, 2015 at 05:39:54AM +0000, Gong, Zhipeng wrote:
> Chris-
> 
> The patch cannot be applied on the latest drm-intel-nightly directly. 
> I modified it a little bit to make it applied.
> The patch can help much in HSW, but a little bit in BDW.
> The test is to transcode 26 streams, which creates 244 threads.
> 
> CPU util      |	w/o patch  |   w/ patch
> ----------------------------------------------------------
> HSW async 1   |   102%     |     61%
> HSW async 5   |   114%     |     46%
> BDW async 1   |   116%     |     116%
> BDW async 5   |   111%     |     107%

The problem on bdw is likely to be frequent inter-ring synchronisation
keeping the number of waiters at 1 (i.e. lack of semaphores). Note that
the first waiter gets the busywait before waiting on the interrupt.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre