drm/i915/gt: Limit frequency drop to RPe on parking
authorChris Wilson <chris@chris-wilson.co.uk>
Tue, 24 Nov 2020 18:35:21 +0000 (18:35 +0000)
committerChris Wilson <chris@chris-wilson.co.uk>
Mon, 30 Nov 2020 17:48:18 +0000 (17:48 +0000)
commitf7ed83cc1925f0b8ce2515044d674354035c3af9
tree7c412e775ce240867d1554f11d12b91380a272d0
parent8d989f4448947c866b47cb6789b88b31d5f79fe3
drm/i915/gt: Limit frequency drop to RPe on parking

We treat idling the GT (intel_rps_park) as a downclock event, and reduce
the frequency we intend to restart the GT with. Since the two workloads
are likely related (e.g. a compositor rendering every 16ms), we want to
carry the frequency and load information from across the idling.
However, we do also need to update the frequencies so that workloads
that run for less than 1ms are autotuned by RPS (otherwise we leave
compositors running at max clocks, draining excess power). Conversely,
if we try to run too slowly, the next workload has to run longer. Since
there is a hysteresis in the power graph, below a certain frequency
running a short workload for longer consumes more energy than running it
slightly higher for less time. The exact balance point is unknown
beforehand, but measurements with 30fps media playback indicate that RPe
is a better choice.

Reported-by: Edward Baker <edward.baker@intel.com>
Tested-by: Edward Baker <edward.baker@intel.com>
Fixes: 043cd2d14ede ("drm/i915/gt: Leave rps->cur_freq on unpark")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Edward Baker <edward.baker@intel.com>
Cc: Andi Shyti <andi.shyti@intel.com>
Cc: Lyude Paul <lyude@redhat.com>
Cc: <stable@vger.kernel.org> # v5.8+
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Andi Shyti <andi.shyti@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201124183521.28623-1-chris@chris-wilson.co.uk
drivers/gpu/drm/i915/gt/intel_rps.c