Fetch/Unpack performance dependent on git version

I thought it might be worth highlighting to people that the performance of the git fetcher *and* the unpack process is highly dependant on the version of git.

Firstly, all versions of git 1.6+ appear to default to injecting an fsync() after fetching objects. fsync() usage significantly hurts our builds. It is also a bit pointless in our usecase, we can however disable it with a simple tweak to the fetcher:

- ud.basecmd = data.getVar("FETCHCMD_git", d, True) or "git"
+ ud.basecmd = data.getVar("FETCHCMD_git", d, True) or "git -c core.fsyncobjectfiles=0"

Secondly, for older versions of git, git clone is running repository coverage checks even for local cloning. E.g.:

git version 1.8.3.2 on my system:

$ bitbake linux-yocto -c fetch
$ time bitbake linux-yocto -c unpack
51.33user 1.93system 1:09.27elapsed 76%CPU (0avgtext+0avgdata 779380maxresident)k

after updating to git 1.9.2:

$ bitbake linux-yocto -c fetch
$ time bitbake linux-yocto -c unpack
4.28user 0.63system 0:04.36elapsed 112%CPU (0avgtext+0avgdata 260692maxresident)k

so 16 times faster!

The commit in question for anyone interested:

https://github.com/git/git/commit/125a05fd0b45416558923b753f6418c24208d443

Michael/Beth: Can we please upgrade the autobuilder to a daisy release buildtools tarball which has git 1.9.x in it? This should massively speed up certain parts of the autobuilder.

Stefan: Could you see which version of git is on the performance benchmark machine? A run with the daisy build tools tarball would be extremely interesting if its before 1.9.

Cheers,

Richard

The new buildtools are installed at /opt/poky/1.6 and I've updated ~pokybuild/.bashrc to source them. Restarting all the buildslaves should put them to use. I'll restart all of them that aren't building currently. opensuse131-a.yp, on the current nightly, is the only one occupied at the moment.

Michael Halstead
Yocto Project / System Administrator