linux-kernel - Re: [PATCH v2 3/3] drm/i915: Move to new PM core fields

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Message-ID: <CAKfTPtBbZgZtU-qZhh-nKoC=cNj=ZT_LTn=cTX4V10MCZhDFEg@mail.gmail.com>
Date:   Mon, 17 Dec 2018 15:21:56 +0100
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Ulf Hansson <ulf.hansson@...aro.org>
Cc:     "open list:THERMAL" <linux-pm@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Thara Gopinath <thara.gopinath@...aro.org>,
        jani.nikula@...ux.intel.com, joonas.lahtinen@...ux.intel.com,
        rodrigo.vivi@...el.com, airlied@...ux.ie,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH v2 3/3] drm/i915: Move to new PM core fields

On Fri, 14 Dec 2018 at 15:36, Ulf Hansson <ulf.hansson@...aro.org> wrote:
>
> On Fri, 14 Dec 2018 at 15:22, Vincent Guittot
> <vincent.guittot@...aro.org> wrote:
> >
> > With jiffies been replaced by raw ns in PM core accounting, 915 driver is
> > updated to use this new time infrastructure.
> >
> > Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
> > ---
> >  drivers/gpu/drm/i915/i915_pmu.c | 12 ++++++------
> >  drivers/gpu/drm/i915/i915_pmu.h |  4 ++--
> >  2 files changed, 8 insertions(+), 8 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/i915_pmu.c b/drivers/gpu/drm/i915/i915_pmu.c
> > index d6c8f8f..cf6437d 100644
> > --- a/drivers/gpu/drm/i915/i915_pmu.c
> > +++ b/drivers/gpu/drm/i915/i915_pmu.c
> > @@ -493,14 +493,14 @@ static u64 get_rc6(struct drm_i915_private *i915)
> >                  */
> >                 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;
> > +                               i915->pmu.suspended_time_last =
> > +                                       kdev->power.suspended_time;
> >
>
> Huh, so patch 2 introduces a complier error because of removing the
> old fields. We can't have that.

I agree
The patch was mainly to raise discussion
>
> Ideally the driver shouldn't touch these fields in the first place,
> but because the fields are defined in a public header, there is always
> a risk that they becomes abused. I would appreciate if we can change
> the driver move away from using these fields and make that a patch
> preceding patch 2.

In fact, the driver doesn't only use some internal fields but also
takes the power.lock
IIUC, the driver wants the current pm runtime suspended time to
estimate a metric when perf events are not accessible
I'm going to send a new version with a runtime pm interface proposal to fix this

Vincent

>
> > -                       val = kdev->power.suspended_jiffies -
> > -                             i915->pmu.suspended_jiffies_last;
> > -                       val += jiffies - kdev->power.accounting_timestamp;
> > +                       val = kdev->power.suspended_time -
> > +                               i915->pmu.suspended_time_last;
> > +                       val += ktime_to_ns(ktime_get()) -
> > +                               kdev->power.accounting_timestamp;
> >
> > -                       val = jiffies_to_nsecs(val);
> >                         val += i915->pmu.sample[__I915_SAMPLE_RC6].cur;
> >
> >                         i915->pmu.sample[__I915_SAMPLE_RC6_ESTIMATED].cur = val;
> > diff --git a/drivers/gpu/drm/i915/i915_pmu.h b/drivers/gpu/drm/i915/i915_pmu.h
> > index 7f164ca..3dc2a30 100644
> > --- a/drivers/gpu/drm/i915/i915_pmu.h
> > +++ b/drivers/gpu/drm/i915/i915_pmu.h
> > @@ -95,9 +95,9 @@ struct i915_pmu {
> >          */
> >         struct i915_pmu_sample sample[__I915_NUM_PMU_SAMPLERS];
> >         /**
> > -        * @suspended_jiffies_last: Cached suspend time from PM core.
> > +        * @suspended_time_last: Cached suspend time from PM core.
> >          */
> > -       unsigned long suspended_jiffies_last;
> > +       u64 suspended_time_last;
> >         /**
> >          * @i915_attr: Memory block holding device attributes.
> >          */
> > --
> > 2.7.4
> >
>
> Kind regards
> Uffe