On Tue, Apr 23, 2019 at 11:45 AM Jeff King <peff@xxxxxxxx> wrote:
>
> On Mon, Apr 22, 2019 at 09:55:38PM -0400, Jeff King wrote:
>
> > Here are my p5302 numbers on linux.git, by the way.
> >
> > Test jk/p5302-repeat-fix
> > ------------------------------------------------------------------
> > 5302.2: index-pack 0 threads 307.04(303.74+3.30)
> > 5302.3: index-pack 1 thread 309.74(306.13+3.56)
> > 5302.4: index-pack 2 threads 177.89(313.73+3.60)
> > 5302.5: index-pack 4 threads 117.14(344.07+4.29)
> > 5302.6: index-pack 8 threads 112.40(607.12+5.80)
> > 5302.7: index-pack default number of threads 135.00(322.03+3.74)
> >
> > which still imply that "4" is a win over "3" ("8" is slightly better
> > still in wall-clock time, but the total CPU rises dramatically; that's
> > probably because this is a quad-core with hyperthreading, so by that
> > point we're just throttling down the CPUs).
>
> And here's a similar test run on a 20-core Xeon w/ hyperthreading (I
> tweaked the test to keep going after eight threads):
>
> Test HEAD
> ----------------------------------------------------
> 5302.2: index-pack 1 threads 376.88(364.50+11.52)
> 5302.3: index-pack 2 threads 228.13(371.21+17.86)
> 5302.4: index-pack 4 threads 151.41(387.06+21.12)
> 5302.5: index-pack 8 threads 113.68(413.40+25.80)
> 5302.6: index-pack 16 threads 100.60(511.85+37.53)
> 5302.7: index-pack 32 threads 94.43(623.82+45.70)
> 5302.8: index-pack 40 threads 93.64(702.88+47.61)
>
> I don't think any of this is _particularly_ relevant to your case, but
> it really seems to me that the default of capping at 3 threads is too
> low.
Looking back at the multithread commit, I think the trend was the same
and I capped it because the gain was not proportional to the number of
cores we threw at index-pack anymore. I would not be opposed to
raising the cap though (or maybe just remove it)
--
Duy
