• Chris Wilson's avatar
    drm/i915/gt: Schedule request retirement when timeline idles · 4f88f874
    Chris Wilson authored
    The major drawback of commit 7e34f4e4 ("drm/i915/gen8+: Add RC6 CTX
    corruption WA") is that it disables RC6 while Skylake (and friends) is
    active, and we do not consider the GPU idle until all outstanding
    requests have been retired and the engine switched over to the kernel
    context. If userspace is idle, this task falls onto our background idle
    worker, which only runs roughly once a second, meaning that userspace has
    to have been idle for a couple of seconds before we enable RC6 again.
    Naturally, this causes us to consume considerably more energy than
    before as powersaving is effectively disabled while a display server
    (here's looking at you Xorg) is running.
    
    As execlists will get a completion event as each context is completed,
    we can use this interrupt to queue a retire worker bound to this engine
    to cleanup idle timelines. We will then immediately notice the idle
    engine (without userspace intervention or the aid of the background
    retire worker) and start parking the GPU. Thus during light workloads,
    we will do much more work to idle the GPU faster...  Hopefully with
    commensurate power saving!
    
    v2: Watch context completions and only look at those local to the engine
    when retiring to reduce the amount of excess work we perform.
    
    Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=112315
    References: 7e34f4e4 ("drm/i915/gen8+: Add RC6 CTX corruption WA")
    References: 2248a283 ("drm/i915/gen8+: Add RC6 CTX corruption WA")
    Signed-off-by: default avatarChris Wilson <chris@chris-wilson.co.uk>
    Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
    Reviewed-by: default avatarTvrtko Ursulin <tvrtko.ursulin@intel.com>
    Link: https://patchwork.freedesktop.org/patch/msgid/20191125105858.1718307-3-chris@chris-wilson.co.uk
    4f88f874
intel_lrc.c 132 KB