• Chris Wilson's avatar
    drm/i915: Tweak RPS thresholds to more aggressively downclock · dd75fdc8
    Chris Wilson authored
    After applying wait-boost we often find ourselves stuck at higher clocks
    than required. The current threshold value requires the GPU to be
    continuously and completely idle for 313ms before it is dropped by one
    bin. Conversely, we require the GPU to be busy for an average of 90% over
    a 84ms period before we upclock. So the current thresholds almost never
    downclock the GPU, and respond very slowly to sudden demands for more
    power. It is easy to observe that we currently lock into the wrong bin
    and both underperform in benchmarks and consume more power than optimal
    (just by repeating the task and measuring the different results).
    
    An alternative approach, as discussed in the bspec, is to use a
    continuous threshold for upclocking, and an average value for downclocking.
    This is good for quickly detecting and reacting to state changes within a
    frame, however it fails with the common throttling method of waiting
    upon the outstanding frame - at least it is difficult to choose a
    threshold that works well at 15,000fps and at 60fps. So continue to use
    average busy/idle loads to determine frequency change.
    
    v2: Use 3 power zones to keep frequencies low in steady-state mostly
    idle (e.g. scrolling, interactive 2D drawing), and frequencies high
    for demanding games. In between those end-states, we use a
    fast-reclocking algorithm to converge more quickly on the desired bin.
    
    v3: Bug fixes - make sure we reset adj after switching power zones.
    
    v4: Tune - drop the continuous busy thresholds as it prevents us from
    choosing the right frequency for glxgears style swap benchmarks. Instead
    the goal is to be able to find the right clocks irrespective of the
    wait-boost.
    Signed-off-by: default avatarChris Wilson <chris@chris-wilson.co.uk>
    Cc: Kenneth Graunke <kenneth@whitecape.org>
    Cc: Stéphane Marchesin <stephane.marchesin@gmail.com>
    Cc: Owen Taylor <otaylor@redhat.com>
    Cc: "Meng, Mengmeng" <mengmeng.meng@intel.com>
    Cc: "Zhuang, Lena" <lena.zhuang@intel.com>
    Reviewed-by: default avatarJesse Barnes <jbarnes@virtuousgeek.org>
    Signed-off-by: default avatarDaniel Vetter <daniel.vetter@ffwll.ch>
    dd75fdc8
i915_irq.c 94.4 KB