[Intel-gfx] [PATCH igt] igt/perf: improve robustness of polling/blocking tests

[Matthew Auld]

On 24 January 2017 at 00:53, Robert Bragg <robert at sixbynine.org> wrote:
> There were a couple of problems with both of these tests that could lead
> to false negatives addressed by this patch.
>
> 1) The upper limit for the number of iterations missed a +1 to consider
>    that there might be a sample immediately available at the start of the
>    loop.
>
> v2) The tests didn't consider that a duration measured in terms of
>    (end-start) ticks could be +- 1 tick since we don't know the
>    fractional part of the tick counts. Our threshold for stime being <
>    one tick could have a false negative for any real stime between 1 to
>    10 milliseconds depending on luck.
>
> The tests now both run for a lot longer (1000 x tick duration, or
> typically 10 seconds each) so that a single tick represents a much
> smaller proportion of the total duration (0.1%) and the stime thresholds
> are now set at 1% of the total duration.
>
> Signed-off-by: Robert Bragg <robert at sixbynine.org>
Reviewed-by: Matthew Auld <matthew.auld at intel.com>