Re: [PATCH v6 6/6] drm/drm-file: Show finer-grained BO sizes in drm_show_memory_stats

[Tvrtko Ursulin]

On 20/09/2023 16:32, Tvrtko Ursulin wrote:
> On 20/09/2023 00:34, Adrián Larumbe 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 contexts of low memory
> > usage.
> >
> > The new selection criteria try to preserve precision, whilst also
> > increasing the display unit selection threshold to render more accurate
> > values.
> >
> > Signed-off-by: Adrián Larumbe <adrian.larumbe@xxxxxxxxxxxxx>
> > Reviewed-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>
> > Reviewed-by: Steven Price <steven.price@xxxxxxx>
> > ---
> >   drivers/gpu/drm/drm_file.c | 5 ++++-
> >   1 file changed, 4 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/drm_file.c b/drivers/gpu/drm/drm_file.c
> > index 762965e3d503..34cfa128ffe5 100644
> > --- a/drivers/gpu/drm/drm_file.c
> > +++ b/drivers/gpu/drm/drm_file.c
> > @@ -872,6 +872,8 @@ void drm_send_event(struct drm_device *dev, struct 
> > drm_pending_event *e)
> >   }
> >   EXPORT_SYMBOL(drm_send_event);
> > +#define UPPER_UNIT_THRESHOLD 100
> > +
> >   static void print_size(struct drm_printer *p, const char *stat,
> >                  const char *region, u64 sz)
> >   {
> > @@ -879,7 +881,8 @@ 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)) &&
>
> IS_ALIGNED worth it at all?
>
> > +            sz < UPPER_UNIT_THRESHOLD * SZ_1K)
> >               break;
>
> Excuse me for a late comment (I was away). I did not get what what is 
> special about a ~10% threshold? Sounds to me just going with the lower 
> unit, when size is not aligned to the higher one, would be better than 
> sometimes precision-sometimes-not.

FWIW both current and the threshold option make testing the feature very 
annoying.

So I'd really propose we simply use smaller unit when unaligned.

Regards,

Tvrtko