• Daniel Vetter's avatar
    drm/i915: use hsw rps tuning values everywhere on gen6+ · 1ee9ae32
    Daniel Vetter authored
    James Bottomley reported [1] a massive power regression, due to the
    enabling of semaphores by default in 3.5. A workaround for him is to
    again disable semaphores. And indeed, his system has a very hard time
    to enter rc6 with semaphores enabled.
    
    Ben Widawsky run around with a kill-a-watt a lot and noticed:
    - There are indeed a few rare systems that seem to have a hard time
      entering rc6 when desktop-idle.
    - One machine, The Indestructible Toshiba regressed in this behaviour
      between 3.5 and 3.6 in a merge commit! So rc6 behaviour with the
      current setting seems to be highly timing dependent and not robust
      at all.
    - The behaviour James reported wrt semaphores seems to be a freak
      timing thing that only happens on his specific machine, confirming
      that enabling semaphores shouldn't reduce rc6 residency.
    
    Now furthermore the Google ChromeOS guys reported [2] a while ago that
    at least on some machines a simply a blinking cursor can keep the gpu
    turbo at the highest frequency. This is because the current rps limits
    used on snb/ivb are highly asymmetric.
    
    On the theory that gpu turbo and rc6 tuning values are related, we've
    tried whether the much saner looking (since much less asymmetric) rps
    tuning values used for hsw would also help entering rc6 more robustly.
    
    And it seems to mostly work, and we don't really have the resources to
    through-roughly tune things in any better way: The values from the
    ChromeOS ppl seem to fare a bit worse for James' machine, so I guess
    we better stick with something vpg (the gpu hw/windows group)
    provided, hoping that they've done their jobs.
    
    Reference[1]: http://lists.freedesktop.org/archives/dri-devel/2012-July/025675.html
    Reference[2]: http://lists.freedesktop.org/archives/intel-gfx/2012-July/018692.html
    Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=53393Tested-by: default avatarBen Widawsky <ben@bwidawsk.net>
    Cc: stable@vger.kernel.org
    Signed-off-by: default avatarDaniel Vetter <daniel.vetter@ffwll.ch>
    1ee9ae32
intel_pm.c 113 KB