Re: Poor performance of git describe in big repos

[Duy Nguyen <pclouds@gmail.com>]

On Thu, May 30, 2013 at 7:29 PM, Alex Bennée <kernel-hacker@bennee.com> wrote:
> I ran perf on it and the top items in the report where:
>
>  41.58%   git  libcrypto.so.1.0.0  [.] 0x6ae73
>  33.96%   git  libz.so.1.2.3.4     [.] 0xe0ec
>  10.39%   git  libz.so.1.2.3.4     [.] adler32
>   2.03%   git  [kernel.kallsyms]   [k] clear_page_c
>
> So I'm guessing it's spending a lot of non-cache efficient time
> un-packing and processing the deltas?

If I'm not mistaken, commits are never deltified. They are usually
small and packed close together for better I/O patterns. If you really
just read hundreds of commits, it can't take that long. Maybe some
code paths accidentally open a tree, a blob or something..

Can you try setting core.logpackaccess to a path on and rerun
describe? Jugding from the code (I never actually tried it), it'll
create a file at the given path with the accessed pack offsets. You
can check what offset corresponds to what object with verify-pack -v.
--
Duy