drm/i915: Interactive RPS mode
RPS provides a feedback loop where we use the load during the previous evaluation interval to decide whether to up or down clock the GPU frequency. Our responsiveness is split into 3 regimes, a high and low plateau with the intent to keep the gpu clocked high to cover occasional stalls under high load, and low despite occasional glitches under steady low load, and inbetween. However, we run into situations like kodi where we want to stay at low power (video decoding is done efficiently inside the fixed function HW and doesn't need high clocks even for high bitrate streams), but just occasionally the pipeline is more complex than a video decode and we need a smidgen of extra GPU power to present on time. In the high power regime, we sample at sub frame intervals with a bias to upclocking, and conversely at low power we sample over a few frames worth to provide what we consider to be the right levels of responsiveness respectively. At low power, we more or less expect to be kicked out to high power at the start of a busy sequence by waitboosting. Prior to commit e9af4ea2 ("drm/i915: Avoid waitboosting on the active request") whenever we missed the frame or stalled, we would immediate go full throttle and upclock the GPU to max. But in commit e9af4ea2, we relaxed the waitboosting to only apply if the pipeline was deep to avoid over-committing resources for a near miss. Sadly though, a near miss is still a miss, and perceptible as jitter in the frame delivery. To try and prevent the near miss before having to resort to boosting after the fact, we use the pageflip queue as an indication that we are in an "interactive" regime and so should sample the load more frequently to provide power before the frame misses it vblank. This will make us more favorable to providing a small power increase (one or two bins) as required rather than going all the way to maximum and then having to work back down again. (We still keep the waitboosting mechanism around just in case a dramatic change in system load requires urgent uplocking, faster than we can provide in a few evaluation intervals.) v2: Reduce rps_set_interactive to a boolean parameter to avoid the confusion of what if they wanted a new power mode after pinning to a different mode (which to choose?) v3: Only reprogram RPS while the GT is awake, it will be set when we wake the GT, and while off warns about being used outside of rpm. v4: Fix deferred application of interactive mode v5: s/state/interactive/ v6: Group the mutex with its principle in a substruct Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=107111 Fixes: e9af4ea2 ("drm/i915: Avoid waitboosting on the active request") Signed-off-by:Chris Wilson <chris@chris-wilson.co.uk> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Radoslaw Szwichtenberg <radoslaw.szwichtenberg@intel.com> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com> Reviewed-by:
Joonas Lahtinen <joonas.lahtinen@linux.intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20180731132629.3381-1-chris@chris-wilson.co.uk
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