Re: Resolving deltas dominates clone time

From: Jeff King <peff@peff.net>
Date: Apr 23, 2019, 04:21 UTC
Message-ID: <20190423042109.GA19183@sigill.intra.peff.net>
In-Reply-To: <20190423015538.GA16369@sigill.intra.peff.net>

On Mon, Apr 22, 2019 at 09:55:38PM -0400, Jeff King wrote:

Show 15 quoted lines

> 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.

-Peff