[RFC PATCH 0/2] grep: make threading smarter

833e3df171 (pack-objects: Add runtime detection of online CPU's, 2008-02-22) added the capability to check the number of online CPUs at runtime to do better threading, so use that as well with grep.

Testing with a large (more than 4) number of cores and no grep.threads configuration in real hardware encouraged, to confirm that no other bottleneck is preventing the additional threads to improve performance.

If platform specific testing shows degradation (specially with HP-UX), make sure that the right number of CPUs is reported by :

  $ ./t/helper/test-tool online-cpus
  4

There are additional cleanups possible in the grep code but had left it out of this RFC to avoid confusion and make the change in patch 2 as straight forward as possible.

There is also a chance that the online_cpus() function will be updated as it predates POSIX and might be associated with one known performance issue in HP-UX[1]

Lastly the performance numbers point to deficiencies in kwset and the compat/regex code that will need to be addressed independently.

Carlo Marcelo Arenas Belón (2):
  p7810: add more grep performance relevant cases
  grep: make default number of threads reflect runtime

 Documentation/git-grep.txt |  2 +-
 builtin/grep.c             |  3 +--
 t/perf/p7810-grep.sh       | 25 +++++++++++++++++++++++--
 3 files changed, 25 insertions(+), 5 deletions(-)

[1] https://public-inbox.org/git/TU4PR8401MB121664A8A588D799803F1E84E11E0@TU4PR8401MB1216.NAMPRD84.PROD.OUTLOOK.COM/