[Bug 76877] New: [BYT]Sysfs RC6 residency counter is inaccurate

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=76877

          Priority: medium
            Bug ID: 76877
                CC: intel-gfx-bugs at lists.freedesktop.org
          Assignee: intel-gfx-bugs at lists.freedesktop.org
           Summary: [BYT]Sysfs RC6 residency counter is inaccurate
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
          Severity: normal
    Classification: Unclassified
                OS: All
          Reporter: wendy.wang at intel.com
          Hardware: Other
            Status: NEW
           Version: unspecified
         Component: DRM/Intel
           Product: DRI

Test on BYT with kernel: 3.14.0-rc8_drm-intel-nightly_19f629_20140331+
Run below script:

    BEFORE=`cat /sys/class/drm/card0/power/rc6_residency_ms`
    time sleep 10    
    AFTER=`cat /sys/class/drm/card0/power/rc6_residency_ms`    
    echo BEFORE = $BEFORE    
    echo AFTER = $AFTER    
    DELTA=$((AFTER - BEFORE))    
    echo DELTA = $DELTA    
    echo "scale=2; ($DELTA / 1000) / 10" | bc -l

Show the result:

real 0m10.002s
user 0m0.000s
sys 0m0.002s
BEFORE = 1281484
AFTER = 1292928
DELTA = 11444
1.14

So there should be something is wrong with Sysfs RC6 residency counter on BYT.

Cannot reproduce this issue on HSW and IVB platform.

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