linux-kernel - Re: [PATCH v9 15/15] drm/i915: Add deadline based boost support

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Date:   Fri, 3 Mar 2023 06:48:43 -0800
From:   Rob Clark <robdclark@...il.com>
To:     Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>
Cc:     Rodrigo Vivi <rodrigo.vivi@...el.com>,
        dri-devel@...ts.freedesktop.org, freedreno@...ts.freedesktop.org,
        Daniel Vetter <daniel@...ll.ch>,
        Christian König <ckoenig.leichtzumerken@...il.com>,
        Michel Dänzer <michel@...nzer.net>,
        Tvrtko Ursulin <tvrtko.ursulin@...el.com>,
        Alex Deucher <alexander.deucher@....com>,
        Pekka Paalanen <ppaalanen@...il.com>,
        Simon Ser <contact@...rsion.fr>,
        Luben Tuikov <luben.tuikov@....com>,
        Rob Clark <robdclark@...omium.org>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        David Airlie <airlied@...il.com>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Christian König <christian.koenig@....com>,
        intel-gfx@...ts.freedesktop.org,
        open list <linux-kernel@...r.kernel.org>,
        "open list:DMA BUFFER SHARING FRAMEWORK" 
        <linux-media@...r.kernel.org>,
        "moderated list:DMA BUFFER SHARING FRAMEWORK" 
        <linaro-mm-sig@...ts.linaro.org>, Matt Turner <mattst88@...il.com>
Subject: Re: [PATCH v9 15/15] drm/i915: Add deadline based boost support

On Fri, Mar 3, 2023 at 1:58 AM Tvrtko Ursulin
<tvrtko.ursulin@...ux.intel.com> wrote:
>
>
> On 03/03/2023 03:21, Rodrigo Vivi wrote:
> > On Thu, Mar 02, 2023 at 03:53:37PM -0800, Rob Clark wrote:
> >> From: Rob Clark <robdclark@...omium.org>
> >>
> >
> > missing some wording here...
> >
> >> v2: rebase
> >>
> >> Signed-off-by: Rob Clark <robdclark@...omium.org>
> >> ---
> >>   drivers/gpu/drm/i915/i915_request.c | 20 ++++++++++++++++++++
> >>   1 file changed, 20 insertions(+)
> >>
> >> diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c
> >> index 7503dcb9043b..44491e7e214c 100644
> >> --- a/drivers/gpu/drm/i915/i915_request.c
> >> +++ b/drivers/gpu/drm/i915/i915_request.c
> >> @@ -97,6 +97,25 @@ static bool i915_fence_enable_signaling(struct dma_fence *fence)
> >>      return i915_request_enable_breadcrumb(to_request(fence));
> >>   }
> >>
> >> +static void i915_fence_set_deadline(struct dma_fence *fence, ktime_t deadline)
> >> +{
> >> +    struct i915_request *rq = to_request(fence);
> >> +
> >> +    if (i915_request_completed(rq))
> >> +            return;
> >> +
> >> +    if (i915_request_started(rq))
> >> +            return;
> >
> > why do we skip the boost if already started?
> > don't we want to boost the freq anyway?
>
> I'd wager Rob is just copying the current i915 wait boost logic.

Yup, and probably incorrectly.. Matt reported fewer boosts/sec
compared to your RFC, this could be the bug

> >> +
> >> +    /*
> >> +     * TODO something more clever for deadlines that are in the
> >> +     * future.  I think probably track the nearest deadline in
> >> +     * rq->timeline and set timer to trigger boost accordingly?
> >> +     */
> >
> > I'm afraid it will be very hard to find some heuristics of what's
> > late enough for the boost no?
> > I mean, how early to boost the freq on an upcoming deadline for the
> > timer?
>
> We can off load this patch from Rob and deal with it separately, or
> after the fact?

That is completely my intention, I expect you to replace my i915 patch ;-)

Rough idea when everyone is happy with the core bits is to setup an
immutable branch without the driver specific patches, which could be
merged into drm-next and $driver-next and then each driver team can
add there own driver patches on top

BR,
-R

> It's a half solution without a smarter scheduler too. Like
> https://lore.kernel.org/all/20210208105236.28498-10-chris@chris-wilson.co.uk/,
> or if GuC plans to do something like that at any point.
>
> Or bump the priority too if deadline is looming?
>
> IMO it is not very effective to fiddle with the heuristic on an ad-hoc
> basis. For instance I have a new heuristics which improves the
> problematic OpenCL cases for further 5% (relative to the current
> waitboost improvement from adding missing syncobj waitboost). But I
> can't really test properly for regressions over platforms, stacks,
> workloads.. :(
>
> Regards,
>
> Tvrtko
>
> >
> >> +
> >> +    intel_rps_boost(rq);
> >> +}
> >> +
> >>   static signed long i915_fence_wait(struct dma_fence *fence,
> >>                                 bool interruptible,
> >>                                 signed long timeout)
> >> @@ -182,6 +201,7 @@ const struct dma_fence_ops i915_fence_ops = {
> >>      .signaled = i915_fence_signaled,
> >>      .wait = i915_fence_wait,
> >>      .release = i915_fence_release,
> >> +    .set_deadline = i915_fence_set_deadline,
> >>   };
> >>
> >>   static void irq_execute_cb(struct irq_work *wrk)
> >> --
> >> 2.39.1
> >>