• Tvrtko Ursulin's avatar
    drm/i915/pmu: Fix sleep under atomic in RC6 readout · 1fe699e3
    Tvrtko Ursulin authored
    We are not allowed to call intel_runtime_pm_get from the PMU counter read
    callback since the former can sleep, and the latter is running under IRQ
    context.
    
    To workaround this, we record the last known RC6 and while runtime
    suspended estimate its increase by querying the runtime PM core
    timestamps.
    
    Downside of this approach is that we can temporarily lose a chunk of RC6
    time, from the last PMU read-out to runtime suspend entry, but that will
    eventually catch up, once device comes back online and in the presence of
    PMU queries.
    
    Also, we have to be careful not to overshoot the RC6 estimate, so once
    resumed after a period of approximation, we only update the counter once
    it catches up. With the observation that RC6 is increasing while the
    device is suspended, this should not pose a problem and can only cause
    slight inaccuracies due clock base differences.
    
    v2: Simplify by estimating on top of PM core counters. (Imre)
    Signed-off-by: default avatarTvrtko Ursulin <tvrtko.ursulin@intel.com>
    Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=104943
    Fixes: 6060b6ae ("drm/i915/pmu: Add RC6 residency metrics")
    Testcase: igt/perf_pmu/rc6-runtime-pm
    Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
    Cc: Chris Wilson <chris@chris-wilson.co.uk>
    Cc: Imre Deak <imre.deak@intel.com>
    Cc: Jani Nikula <jani.nikula@linux.intel.com>
    Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
    Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
    Cc: David Airlie <airlied@linux.ie>
    Cc: intel-gfx@lists.freedesktop.org
    Cc: dri-devel@lists.freedesktop.org
    Reviewed-by: default avatarChris Wilson <chris@chris-wilson.co.uk>
    Link: https://patchwork.freedesktop.org/patch/msgid/20180206183311.17924-1-tvrtko.ursulin@linux.intel.com
    1fe699e3
i915_pmu.c 25.8 KB