From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Ebbo <david.ebbo@gmail.com>
Subject: Seeing high CPU usage during git-upload-pack
Date: Wed, 9 May 2012 00:01:37 -0700
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We=92re using git-upload-pack in a simple git server. When the repo is
on a slow share, we=92re noticing that git-upload-pack is hugging the
CPU during the whole pack-objects operation.

More details:

- git-upload-pack gets launched (with params git-upload-pack
--stateless-rpc //path/to/repo)
- it itself launches a git process (with params pack-objects --revs
--all --stdout --progress --delta-base-offset). This git process is
the one that does all the disk I/O, but it's not the one using up the
CPU time.
- git-upload-pack appears to be waiting for the git process, and is at
high CPU during that time, suggesting that it's doing some kind of
busy wait. To further test that, I stopped the git process in the
debugger, preventing it from making progress. At that point,
git-upload-pack pegs the CPU forever.

Would someone familiar with the sources be able to comment on this
busy wait behavior, and on whether it could conceivably be done in a
way that doesn=92t use up some much CPU?

Thanks,
David