[Mesa-dev] [PATCH 3/4] radeonsi: add more unlikely() uses into si_draw_vbo

[Marek Olšák]

On Sep 6, 2016 12:03 PM, "Michel Dänzer" <michel at daenzer.net> wrote:
>
> On 06/09/16 06:04 PM, Marek Olšák wrote:
> > On Tue, Sep 6, 2016 at 3:54 AM, Michel Dänzer <michel at daenzer.net>
wrote:
> >> On 06/09/16 07:46 AM, Marek Olšák wrote:
> >>> From: Marek Olšák <marek.olsak at amd.com>
> >>
> >> Did you measure any significant performance boost with this change?
> >
> > I didn't measure anything.
> >
> >> Otherwise, using (un)likely can be bad because it can defeat the CPU's
> >> branch prediction, which tends to be pretty good these days.
> >
> > I'm not an expert on that, but it doesn't seem to be the case
> > according to other people's comments here.
>
> My main point (which Gustaw seems to agree with) is that (un)likely
> should only be used when measurements show that they have a positive
effect.

I agree with you, but do you always measure the effect of unlikely? I
almost never do and I just use it instinctively like most people do. Due to
our manpower constraints, we can't even afford to measure performance for
much bigger changes than this.

Marek

Marek

>
>
> --
> Earthling Michel Dänzer               |               http://www.amd.com
> Libre software enthusiast             |             Mesa and X developer
>
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