[Bug 62710] New: [IVB bisected]x11perf performance reduced by 40%

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=62710

          Priority: medium
            Bug ID: 62710
          Assignee: intel-gfx-bugs at lists.freedesktop.org
           Summary: [IVB bisected]x11perf performance reduced by 40%
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
          Severity: normal
    Classification: Unclassified
                OS: All
          Reporter: mengmeng.meng at intel.com
          Hardware: Other
            Status: NEW
           Version: unspecified
         Component: DRM/Intel
           Product: DRI

System Environment:       
--------------------------
Platform:IVB
Libdrm: (master)libdrm-2.4.42-7-g36a2daad2416ad55a859c483b0d7ed93a5eff6e0
Mesa:   (9.1)e6616948b74531eae3137585b3ae35a1fc0f8174
Xserver:(server-1.13-branch)xorg-server-1.13.3
Xf86_video_intel:(master)2.21.5-1-g9f8e86800345d19785eae2dd2099dd7d61a7a3b3
Kernel: (drm-intel-fixes) c12aba5aa0e60b7947bc8b6ea25ef55c4acf81a4

Bug detailed description:
-----------------------------
x11perf performance reduced by 40% on IVB. The problem exists on both xinit and
gnome-session. It's kernel regression, by bisected show 3b4f819d5eac94ba8fe5 is
the first bad commit.

commit 3b4f819d5eac94ba8fe5e8c061f6dabfe8d7b22c
Author: Takashi Iwai <tiwai at suse.de>
Date:   Mon Mar 11 18:40:16 2013 +0100
    Revert "drm/i915: try to train DP even harder"

Performance data
-------------------
x11perf -aa10text on IVB.
                   gnome-session         xinit               
good(3118a)        3620000.0/sec        4230000.0/sec       
bad(3b4f81)        2300000.0/sec        2480000.0/sec

Reproduce steps:
----------------------------
1, xinit&
2, vblank_mode=0 x11perf -aa10text

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