[Mesa-dev] [PATCH 9/9] i965/drm: Add stall warnings when mapping or waiting on BOs.

[Chris Wilson]

On Mon, Apr 10, 2017 at 10:29:50AM -0700, Kenneth Graunke wrote:
> On Monday, April 10, 2017 1:31:11 AM PDT Chris Wilson wrote:
> > In general, does 10us resolution require compensation for clock_gettime()
> > overhead and checking against clock_getres()?
> 
> FWIW, I copied the 10us threshold from your brw-batch series.  I'm happy
> to adjust it.

I can honestly say there wasn't any thought behind it. :)
I think it's about the right sort of threshold between "free" and "don't
do this". A hundred "don't do this" really eats into your frame budget!
 
> On my system, clock_getres(CLOCK_MONOTONIC[_RAW], &res) reports a
> resolution of 1 nanosecond, so given a 10us = 10000ns threshold, I
> doubt we need to consider it.

Best to check on an atom - though I doubt any are as bad as Pineview
(which was ~4ms iirc). MONOTONIC_RAW should be close to tsc resolution,
so yes if we have RAW, we probably don't need to worry. Just do a check
and warn if than the alarm threshold  and see if anybody ever files a
bug.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre