igt/perf_pmu: Tighten measurements for most-busy

Create all the spinners before starting the sampler and then measure how
long we sleep.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=104160
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
1 file changed