[Bugme-new] [Bug 41892] New: drm_mode_cursor_ioctl high latency

[bugzilla-daemon at bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=41892

           Summary: drm_mode_cursor_ioctl high latency
           Product: Drivers
           Version: 2.5
          Platform: All
        OS/Version: Linux
              Tree: Mainline
            Status: NEW
          Severity: normal
          Priority: P1
         Component: Video(DRI - Intel)
        AssignedTo: drivers_video-dri-intel at kernel-bugs.osdl.org
        ReportedBy: lex4051 at gmail.com
        Regression: No


Created an attachment (id=70692)
 --> (https://bugzilla.kernel.org/attachment.cgi?id=70692)
sudo lspci -vvv

After kernel update I noticed strange problem with screen: when I do something
without moving cursor most of thing works fine, but if I move cursor every 5-15
seconds screen freezes for a while... and then everything works fine. I
recompiled kernel to use latencytop and found that this latency is caused by
drm_mode_cursor_ioctl which takes about 750..1000ms (but in "good-working"
kernel this takes 20-25ms). I used "git bisect" to find the exact point of the
problem:

bad is "a6360dd37e1a144ed11e6548371bade559a1e4df" (tag v2.6.39-rc3)
good is "0ce790e7d736cedc563e1fb4e998babf5a4dbc3d" (tag v2.6.39-rc1)

The result was "7f58aabc369014fda3a4a33604ba0a1b63b941ac": using kernel source
from this commit causes the problem, using previous
("9f01b25048ad12b5d71f4f7d3b62ef737639a08d") does not.


System description (with "good-working" kernel):
# uname -a
Linux LeX-laptop 2.6.39-rc1-ARCH-00002-geccaca2-dirty #14 SMP PREEMPT Sun Aug
28 18:38:20 MSK 2011 x86_64 Genuine Intel(R) CPU U4100 @ 1.30GHz GenuineIntel
GNU/Linux

# cat /proc/version
Linux version 2.6.39-rc1-ARCH-00002-geccaca2-dirty (lex at LeX-PC) (gcc version
4.6.1 20110819 (prerelease) (GCC) ) #14 SMP PREEMPT Sun Aug 28 18:38:20 MSK
2011

# cat /proc/cmdline
BOOT_IMAGE=/vmlinuz-linux-git root=/dev/sda3 ro max_loop=8 ipv6.disable=1
i915.modeset=1

# sudo lspci -vvv
(see attachment)

The machine is laptop: Samsung x420-fa02ru.

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