[Bug 102983] New: [SKL][regression][bisected] Performance regression after linux 4.7

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=102983

            Bug ID: 102983
           Summary: [SKL][regression][bisected] Performance regression
                    after linux 4.7
           Product: DRI
           Version: DRI git
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: normal
          Priority: medium
         Component: DRM/Intel
          Assignee: intel-gfx-bugs at lists.freedesktop.org
          Reporter: ross at kallisti.us
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
                CC: intel-gfx-bugs at lists.freedesktop.org

Created attachment 134473
  --> https://bugs.freedesktop.org/attachment.cgi?id=134473&action=edit
log from bisection

In Linux 4.7 and earlier, RimWorld (a steam game) ran at 60fps on my laptop. 
With any later kernel release, the game runs at 30-40fps, stutters, and has
severe input latency.  The issue is 100% reproducible.  drm-tip (6aa0df37d3fc)
exhibits the same issue.


Hardware info: Skylake i7-6700HQ, Dell XP 9550.  The laptop also has an nvidia
gpu.  The issue affects both gpus, but testing purposes, I've only used the
intel gpu.

Software info: Debian stretch, x86_64

Bisection details:  good commit v4.7, bad commit v4.8-rc1.  This leads to a DRM
commit:

a59c2086fe9c489e0a2a86e080ba is the first bad commit
commit ea0000f0d369a59c2086fe9c489e0a2a86e080ba
Author: Daniel Vetter <daniel.vetter at ffwll.ch>
Date:   Mon Jun 13 16:13:46 2016 +0200

    drm/i915: Roll out the helper nonblock tracking

    Right now still all blocking, no worker anywhere to be seen.

    Reviewed-by: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
    Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
    Link:
http://patchwork.freedesktop.org/patch/msgid/1465827229-1704-2-git-send-email-daniel.vetter@ffwll.ch

To be attached:
- git bisect log
- dmesg w/ drm.debug=0xe from 4.7.8
- dmesg w/ drm.debug=0xe from drm-tip

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