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: <CAF6AEGtzOS89V1vbobpSEb9KX8x9T0FfmkW2OAaxAKLs+GugKA@mail.gmail.com>
Date:   Tue, 12 Sep 2023 18:46:52 -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
Subject: Re: [PATCH v4 6/6] drm/drm-file: Show finer-grained BO sizes in drm_show_memory_stats

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.

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)
> > +             if (sz & (SZ_1K - 1))
> >                       break;
> >               sz = div_u64(sz, SZ_1K);
> >       }
>