linux-kernel - Re: [PATCH 3/3] drm/msm: Expose client engine utilization via fdinfo

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Date:   Mon, 28 Feb 2022 08:01:34 -0800
From:   Rob Clark <robdclark@...il.com>
To:     Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>
Cc:     dri-devel <dri-devel@...ts.freedesktop.org>,
        freedreno <freedreno@...ts.freedesktop.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Rob Clark <robdclark@...omium.org>,
        Sean Paul <sean@...rly.run>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] drm/msm: Expose client engine utilization via fdinfo

On Mon, Feb 28, 2022 at 6:33 AM Tvrtko Ursulin
<tvrtko.ursulin@...ux.intel.com> wrote:
>
>
> On 25/02/2022 22:14, Rob Clark wrote:
> > On Fri, Feb 25, 2022 at 12:25 PM Rob Clark <robdclark@...il.com> wrote:
> >>
> >> From: Rob Clark <robdclark@...omium.org>
> >>
> >> Similar to AMD commit
> >> 874442541133 ("drm/amdgpu: Add show_fdinfo() interface"), using the
> >> infrastructure added in previous patches, we add basic client info
> >> and GPU engine utilisation for msm.
> >>
> >> Example output:
> >>
> >>          # cat /proc/`pgrep glmark2`/fdinfo/6
> >>          pos:    0
> >>          flags:  02400002
> >>          mnt_id: 21
> >>          ino:    162
> >>          drm-driver:     msm
> >>          drm-client-id:  7
> >>          drm-engine-gpu: 1734371319 ns
> >>          drm-cycles-gpu: 1153645024
>
> Nice, so my vendor agnostic actually worked (with that single fixup of
> accounting for the fact pdev tag is optional)?
>
> > Note that it might be useful to have a standardized way to report # of
> > cycles and max freq, so userspace tool can derive %utilization in
> > addition to just %busy
>
> How do you define %utilisation vs %busy - I don't exactly follow since I
> see the two as same?

so, say you are running at 50% of max clk, and gpu is busy 70% of the
time.  The utilization is only 35% because the gpu could scale up the
clk to get more work done.

> Looking at your patch I guess I don't understand the difference between
> 'elapsed' and 'cycles' inside your retire_submit(). Both are scoped to a
> single context and are not global? If 'elapsed' is time context has
> spent on the GPU, cycles isn't the same just in a different unit?

Correct, we capture (from GPU cmdstream) two counters both before and
after a submit (aka execbuf) runs, one is a fixed-rate counter, which
gives us elapsed time.  The second is a counter that increments every
clk cycle, which gives us the # of cycles.  With the two values, we
can calculate GPU frequency.

BR,
-R

> Regards,
>
> Tvrtko
>