Re: [PATCH] Use strict priority ranking for pq gen() benchmarking

[Song Liu <song@kernel.org>]

On Mon, Jan 3, 2022 at 8:28 AM Dirk Müller <dmueller@suse.de> wrote:
>
> On Sonntag, 2. Januar 2022 01:03:44 CET Song Liu wrote:
>
> > We need  more explanation/documentation about 0 vs. 1 vs. 2 priority.
>
> In the commit message? in the code? this is basically a copy&paste of the same
> concept and code from a few lines below the diff, struct raid6_recov_calls
> which works the same way and currently has no documentation at all.
>
> want me to add to both then?

I guess we only need something like:

  .priority = 2   /* avx is always faster than sse */

>
> > >                         if ((*algo)->valid && !(*algo)->valid())
> >
> > If the module load time is really critical, maybe we can run all
> > ->valid() calls first and
> > find the highest valid priority. Then, we only run the benchmark for
> > these algorithms.
>
> thats exactly what the code always did. previously all x86_64 specific
> implementations (be it SSE1/SSE2/AVX2/AVX512) all had the same priority level
> 1, over the default priority level 0 for the implemented-in-C int*.c routines.
> with this change, we have one more level p refering AVX* over the rest, so
> that we skip testing SSE1/SSE2 (similary to how the integer implementations
> have always been skipped before).
>
> > Does this make sense?
>
> the valid call is not probing anything by itself. it just iterates over a
> small array of functions and stops executing benchmarks for those that have
> lower priority ranks.
>
> so there isn't really a lot of cycles to win by changing the execution order
> here. I would assume it will actually slow things down as we have to store the
> valid() result for the 2nd iteration.

Let's keep this part as-is then.

Thanks,
Song