[Bug 103886] [CI] igt at perf_pmu@multi-client-vecs0 - fail - Failed assertion: (double)(val[1]) <= (1.0 + (tolerance)) * (double)(slept) && (double)(val[1]) >= (1.0 - (tolerance)) * (double)(slept)

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=103886

Chris Wilson <chris at chris-wilson.co.uk> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|NEW                         |RESOLVED

--- Comment #1 from Chris Wilson <chris at chris-wilson.co.uk> ---
Final cleanup (we hope):

commit 8ee4f19c47031f23340055da4d9f2af537de23f4
Author: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
Date:   Fri Nov 24 09:49:59 2017 +0000

    drm/i915/pmu: Stop averaging with the previous sample

    Averaging with the previous sample brings a small statistical improvement
    to sampling counters, but can leek a little bit of state from a current
    client to the next which mulls the border between past and present for
    observing clients.

    This is because on event enable clients record the current counter value
    and use it as reference, but with rapid off-on event cycles, and due the
    delayed nature of sampling timer self-disarm, previous sample value does
    not get cleared under these circumstances.

    Solution is to stop averaging with the previous sample. This has a small
    downside of losing some precision with short and spiky signals, but the
    alternatives look too complicated for the benefit.

    Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
    Cc: Chris Wilson <chris at chris-wilson.co.uk>
    Cc: Sagar Arun Kamble <sagar.a.kamble at intel.com>
    Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>
    Tested-by: Chris Wilson <chris at chris-wilson.co.uk>
    Link:
https://patchwork.freedesktop.org/patch/msgid/20171124094959.10725-1-tvrtko.ursulin@linux.intel.com

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