On 1/17/2019 8:23 AM, Ævar Arnfjörð Bjarmason wrote:
Slightly optimize the "commit-graph write" step by using
FOR_EACH_OBJECT_PACK_ORDER with for_each_object_in_pack(). See commit
[1] and [2] for the facility and a similar optimization for "cat-file".
On Linux it is around 5% slower to run:
echo 1 >/proc/sys/vm/drop_caches &&
cat .git/objects/pack/* >/dev/null &&
git cat-file --batch-all-objects --batch-check --unordered
Than the same thing with the "cat" omitted. This is as expected, since
we're iterating in pack order and the "cat" is extra work.
Before this change the opposite was true of "commit-graph write". We
were 6% faster if we first ran "cat" to efficiently populate the FS
cache for our sole big pack on linux.git than if we had it populated
via for_each_object_in_pack(). Now we're 3% faster without the "cat"
instead.
The tests were done on an unloaded Linux 3.10 system with 10 runs for
each.
1. 736eb88fdc ("for_each_packed_object: support iterating in
pack-order", 2018-08-10)
2. 0750bb5b51 ("cat-file: support "unordered" output for
--batch-all-objects", 2018-08-10)
Thanks, Aevar! I plan to give this a test on the Windows repository, as
this is the way we generate the commit-graph in VFS for Git.
I created a PR on microsoft/git [1] and am generating the installers now [2]
[1] https://github.com/Microsoft/git/pull/110
[2] https://dev.azure.com/gvfs/ci/_build/results?buildId=6114
The code itself looks good, I just need to double-check the performance
numbers.
Thanks,
-Stolee
