[Bug 87726] New: [BDW Bisected] OglDrvCtx performance reduced by ~30% after use true PPGTT in Gen8+

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=87726

            Bug ID: 87726
           Summary: [BDW Bisected] OglDrvCtx performance reduced by ~30%
                    after use true PPGTT in Gen8+
           Product: DRI
           Version: unspecified
          Hardware: Other
                OS: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: DRM/Intel
          Assignee: intel-gfx-bugs at lists.freedesktop.org
          Reporter: wendy.wang at intel.com
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
                CC: intel-gfx-bugs at lists.freedesktop.org

Environment:
-----------------------------------
Platform: BDW

 Libdrm:       
(master)libdrm-2.4.58-19-gf99522e678dbbaffeca9462a8edcbe900574dc12
 Mesa:        (master)873d7351c5a696b6f8493c907eb8c76b8cb632da
 Xserver:       
(master)xorg-server-1.16.99.901-98-g0f5fdaf600bfeada966aea942cb3e347d4efee30
 Xf86_video_intel:       
(master)2.99.916-177-g99537089346ed7a1bc6b02349fad93845e865bb9
 Cairo:        (master)4a225fca5f121c31ddaa0af80a13bf95a7f21a5b
 Libva:        (master)8986ec692b19d8dd6bd2aa118b5dffbd05a8f909
 Libva_intel_driver:        (master)b5d6d9d425a6d539b27d22992bda05f79d1a0622
 Kernel:   (drm-intel-nightly)8d22327ae006186bad9f95c300fad5ecd5e961a4

Bug detailed description:
---------------------------------------------
 OglDrvCtx performance reduced by ~30% after use true PPGTT in Gen8+

Bisect drm-intel-next-queued kernel branch, the first bad commit is:

2f82bbdf3d4f1361c3d713c516d8aa390102374d is the first bad commit
commit 2f82bbdf3d4f1361c3d713c516d8aa390102374d
Author: Michel Thierry <michel.thierry at intel.com>
Date: Mon Dec 15 14:58:00 2014 +0000

    drm/i915: Use true PPGTT in Gen8+ when execlists are enabled

    In Gen8+, full ppgtt needs execlist, otherwise the ctx switch can hang.

    Also remove the current restriction, a user should be able to explicitly
set
    ppgtt=2.



Reproduce steps:
---------------------------------------------
1,   xinit &    
2,   cd /usr/local/games/OpenGL/SynMark2_6
3.   ./synmark2 OglDrvCtx

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