linux-kernel - Re: [PATCH v4 6/6] drm/drm-file: Show finer-grained BO sizes in drm_show_memory

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Message-ID: <CAF6AEGu+NeMfeP3yVLr76fUmXeWPx86D9ckw_WjXu+Xpn6DJvA@mail.gmail.com>
Date:   Wed, 13 Sep 2023 09:46:45 -0700
From:   Rob Clark <robdclark@...il.com>
To:     Boris Brezillon <boris.brezillon@...labora.com>
Cc:     Adrián Larumbe <adrian.larumbe@...labora.com>,
        maarten.lankhorst@...ux.intel.com, mripard@...nel.org,
        tzimmermann@...e.de, airlied@...il.com, daniel@...ll.ch,
        quic_abhinavk@...cinc.com, dmitry.baryshkov@...aro.org,
        sean@...rly.run, marijn.suijten@...ainline.org, robh@...nel.org,
        steven.price@....com, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        healych@...zon.com, kernel@...labora.com,
        freedreno@...ts.freedesktop.org,
        Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>
Subject: Re: [PATCH v4 6/6] drm/drm-file: Show finer-grained BO sizes in drm_show_memory_stats

On Wed, Sep 13, 2023 at 12:36 AM Boris Brezillon
<boris.brezillon@...labora.com> wrote:
>
> On Tue, 12 Sep 2023 19:14:35 -0700
> Rob Clark <robdclark@...il.com> wrote:
>
> > On Tue, Sep 12, 2023 at 6:46 PM Rob Clark <robdclark@...il.com> wrote:
> > >
> > > On Tue, Sep 12, 2023 at 2:32 AM Boris Brezillon
> > > <boris.brezillon@...labora.com> wrote:
> > > >
> > > > On Tue, 12 Sep 2023 09:37:00 +0100
> > > > Adrián Larumbe <adrian.larumbe@...labora.com> wrote:
> > > >
> > > > > The current implementation will try to pick the highest available size
> > > > > display unit as soon as the BO size exceeds that of the previous
> > > > > multiplier. That can lead to loss of precision in BO's whose size is
> > > > > not a multiple of a MiB.
> > > > >
> > > > > Fix it by changing the unit selection criteria.
> > > > >
> > > > > For much bigger BO's, their size will naturally be aligned on something
> > > > > bigger than a 4 KiB page, so in practice it is very unlikely their display
> > > > > unit would default to KiB.
> > > >
> > > > Let's wait for Rob's opinion on this.
> > >
> > > This would mean that if you have SZ_1G + SZ_1K worth of buffers, you'd
> > > report the result in KiB.. which seems like overkill to me, esp given
> > > that the result is just a snapshot in time of a figure that
> > > realistically is dynamic.
>
> Yeah, my point was that, generally, such big buffers tend to have
> a bigger size alignment (like 2MB for anything bigger than 1GB), but
> maybe this assumption doesn't stand for all drivers.

Maybe for CMA?  Regardless, this # is the sum of buffer sizes, so you
could still get that 1G+1K scenario

> > >
> > > Maybe if you have SZ_1G+SZ_1K worth of buffers you should report the
> > > result with more precision than GiB, but more than MiB seems a bit
> > > overkill.
> > >
> > > BR,
> > > -R
> > >
> > > > >
> > > > > Signed-off-by: Adrián Larumbe <adrian.larumbe@...labora.com>
> > > > > ---
> > > > >  drivers/gpu/drm/drm_file.c | 2 +-
> > > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > > >
> > > > > diff --git a/drivers/gpu/drm/drm_file.c b/drivers/gpu/drm/drm_file.c
> > > > > index 762965e3d503..bf7d2fe46bfa 100644
> > > > > --- a/drivers/gpu/drm/drm_file.c
> > > > > +++ b/drivers/gpu/drm/drm_file.c
> > > > > @@ -879,7 +879,7 @@ static void print_size(struct drm_printer *p, const char *stat,
> > > > >       unsigned u;
> > > > >
> > > > >       for (u = 0; u < ARRAY_SIZE(units) - 1; u++) {
> > > > > -             if (sz < SZ_1K)
> >
> > btw, I was thinking more along the lines of:
> >
> >    if (sz < 10*SZ_1K)
> >
> > (or perhaps maybe 100*SZ_1K)
>
> I think I suggested doing that at some point:
>
>                 if ((sz & (SZ_1K - 1)) &&
>                     sz < UPPER_UNIT_THRESHOLD * SZ_1K)
>                         break;
>
> so we can keep using the upper unit if the size is a multiple of this
> upper unit, even if it's smaller than the selected threshold.

yeah, that wfm

BR,
-R

>
> >
> > I mean, any visualization tool is going to scale the y axis based on
> > the order of magnitude.. and if I'm looking at the fdinfo with my
> > eyeballs I don't want to count the # of digits manually to do the
> > conversion in my head.  The difference btwn 4 or 5 or maybe 6 digits
> > is easy enough to eyeball, but more than that is too much for my
> > eyesight, and I'm not seeing how it is useful ;-)
> >
> > But if someone really has a valid use case for having precision in 1KB
> > then I'm willing to be overruled.
>
> So, precision loss was one aspect, but my main concern was having
> things displayed in KiB when they could have been displayed in MiB,
> because the size is a multiple of a MiB but still not big enough to
> pass the threshold test (which was set to 10000x in the previous
> version).
>
> > But I'm not a fan of the earlier
> > approach of different drivers reporting results differently, the whole
> > point of fdinfo was to have some standardized reporting.
>
> Totally agree with that.
>
> >
> > BR,
> > -R
> >
> > > > > +             if (sz & (SZ_1K - 1))
> > > > >                       break;
> > > > >               sz = div_u64(sz, SZ_1K);
> > > > >       }
> > > >
>