Messages in this thread | | | Subject | Re: [Intel-gfx] [PATCH v5 2/3] drm/i915: Move on the new pm runtime interface | From | Tvrtko Ursulin <> | Date | Mon, 31 Dec 2018 12:32:26 +0000 |
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On 21/12/2018 13:26, Vincent Guittot wrote: > On Fri, 21 Dec 2018 at 12:33, Tvrtko Ursulin > <tvrtko.ursulin@linux.intel.com> wrote: >> >> >> Hi, >> >> On 21/12/2018 10:33, Vincent Guittot wrote: >>> Use the new pm runtime interface to get the accounted suspended time: >>> pm_runtime_suspended_time(). >>> This new interface helps to simplify and cleanup the code that computes >>> __I915_SAMPLE_RC6_ESTIMATED and to remove direct access to internals of >>> PM runtime. >>> >>> Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org> >>> Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org> >>> --- >>> drivers/gpu/drm/i915/i915_pmu.c | 16 ++++++---------- >>> drivers/gpu/drm/i915/i915_pmu.h | 4 ++-- >>> 2 files changed, 8 insertions(+), 12 deletions(-) >>> >>> diff --git a/drivers/gpu/drm/i915/i915_pmu.c b/drivers/gpu/drm/i915/i915_pmu.c >>> index d6c8f8f..3f76f60 100644 >>> --- a/drivers/gpu/drm/i915/i915_pmu.c >>> +++ b/drivers/gpu/drm/i915/i915_pmu.c >>> @@ -5,6 +5,7 @@ >>> */ >>> >>> #include <linux/irq.h> >>> +#include <linux/pm_runtime.h> >>> #include "i915_pmu.h" >>> #include "intel_ringbuffer.h" >>> #include "i915_drv.h" >>> @@ -478,7 +479,6 @@ static u64 get_rc6(struct drm_i915_private *i915) >>> * counter value. >>> */ >>> spin_lock_irqsave(&i915->pmu.lock, flags); >>> - spin_lock(&kdev->power.lock); >>> >>> /* >>> * After the above branch intel_runtime_pm_get_if_in_use failed >>> @@ -491,16 +491,13 @@ static u64 get_rc6(struct drm_i915_private *i915) >>> * suspended and if not we cannot do better than report the last >>> * known RC6 value. >>> */ >>> - if (kdev->power.runtime_status == RPM_SUSPENDED) { >>> - if (!i915->pmu.sample[__I915_SAMPLE_RC6_ESTIMATED].cur) >>> - i915->pmu.suspended_jiffies_last = >>> - kdev->power.suspended_jiffies; >>> + if (pm_runtime_status_suspended(kdev)) { >>> + val = pm_runtime_suspended_time(kdev); >> >> There is a race condition between the status check and timestamp access >> which the existing code solves by holding the power.lock over it. But I >> don't exactly remember how this issue was manifesting. Is >> kdev->power.suspended_jiffies perhaps reset on exit from runtime >> suspend, which was then underflowing the val, not sure. >> >> Anyways, is the new way of doing this safe with regards to this race? In > > AFAICT it is safe. > The current version does: > 1-take lock, > 2-test if dev is suspended > 3-read some internals field to computed an up-to-date suspended time > 4-update __I915_SAMPLE_RC6_ESTIMATED > 5-release lock > > The new version does: > 1-test if dev is suspended > 2-get an up-to-date suspended time with pm_runtime_suspended_time. > This is atomic and monotonic > 3-update __I915_SAMPLE_RC6_ESTIMATED > > A change from suspended to another states that happens just before > step 1 is ok for both as we will run the else if > No change of the state can happen after step 1 in current code and the > estimated suspended time will be the time up to step2. In parallel, > Any state change will have to wait step5 to continue > If a change from suspended to another state happens after step 1 in > new code, the suspended time return by PM core will be the time up to > this change. So I would say you don't delay state transition and you > get a more accurate estimated suspended time (even if the difference > should be small). > If a change from suspended to another state happens after step 2 in > new code, the suspended time return by PM core will be the time up to > step 2 so there is no changes > > >> other words is the value pm_runtime_suspended_time always monotonic, >> even when not suspended? If not we have to handle the race somehow. > > Yes pm_runtime_suspended_time is monotonic and stays unchanged when > not suspended > >> >> If it is always monotonic, then worst case we report one wrong sample, >> which I guess is still not ideal since someone could be querying the PMU >> with quite low frequency. >> >> There are tests which probably can hit this, but to run them >> automatically your patches would need to be rebased on drm-tip and maybe >> sent to our trybot. I can do that after the holiday break if you are >> okay with having the series waiting until then. > > yes looks good to me
Looks good to me as well. And our CI agrees with it. So:
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
I assume you will take the patch through some power related tree and we will eventually pull it back to drm-tip.
Regards,
Tvrtko
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