[PATCH 0/3] index-pack threading defaults

[Jeff King <peff@peff.net>]

I decided to revisit index-pack's hard-coded default of 3 threads. And
it turns out that higher numbers perform much better. :)

That value was determined experimentally in 2012. I'm not sure of the
exact reason it's different now (modern processors are better at
parallelism, or modern git is better at parallelism, or the original
experiment was just a fluke). But regardless, I can get on the order of
a two-to-one speedup by bumping the thread count. See the final patch
for timings and more specific discussion.

The first two patches are just perf-test improvements (actually, the
slowness to value ratio of p5302 from the first patch is why I was
looking at this at all).

  [1/3]: p5302: disable thread-count parameter tests by default
  [2/3]: p5302: count up to online-cpus for thread tests
  [3/3]: index-pack: adjust default threading cap

 builtin/index-pack.c       | 19 ++++++++++++---
 t/perf/README              |  9 ++++++++
 t/perf/p5302-pack-index.sh | 47 +++++++++++++++++++-------------------
 t/perf/perf-lib.sh         |  2 ++
 4 files changed, 51 insertions(+), 26 deletions(-)

-Peff