[Bug 102670] [CI] igt at kms_cursor_legacy@*flip-vs-cursor-* Failed assertion: get_vblank(display->drm_fd, pipe, 0) == *

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=102670

Arek Hiler <arkadiusz.hiler at intel.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
      i915 platform|BXT, GLK, HSW, I915G, KBL,  |ALL
                   |SKL, SNB                    |
         QA Contact|intel-gfx-bugs at lists.freede |
                   |sktop.org                   |
           Assignee|intel-gfx-bugs at lists.freede |dri-devel at lists.freedesktop
                   |sktop.org                   |.org
                 CC|                            |arkadiusz.hiler at intel.com
          Component|DRM/Intel                   |IGT

--- Comment #17 from Arek Hiler <arkadiusz.hiler at intel.com> ---
The test seems to be very prone to race conditions and this may explain the
sporadic failures we see (few instances every week, affects all the machines):

1. we try to figure out experimentally how many cursor updates we can squeeze
between vblanks, by starting with a high number and lowering it until we fit.
Our target is a quarter of that
2. we pin our process to a CPU and fork a busy loop with sched_yield();
3. 150 loops of trying to squeeze target cursor updates within one vblank

This doesn't take power and thermal budged into account and makes a lot of
assumptions about process scheduling on a non-RTOS.

User impact is low. We loose some coverage. Test needs to be reworked.

Immediate steps:
1. log the delta between vblanks, so we can regain some coverage by having
better filters
2. log our target
3. don't exit early, show how many iterations of the 150 had failed

This is related and it makes sense to work on both together:
https://bugs.freedesktop.org/show_bug.cgi?id=103355

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