Re: [PATCH] check_refname_component: Optimize

From: Jeff King <peff@peff.net>
Date: May 29, 2014, 23:41 UTC
Message-ID: <20140529234109.GA28683@sigill.intra.peff.net>
In-Reply-To: <CACsJy8BS_YhMB9ZZRx4faj=_YWZQrqm7B9AHkTGye=okja=m-Q@mail.gmail.com>

On Fri, May 30, 2014 at 06:24:30AM +0700, Duy Nguyen wrote:

Show 13 quoted lines

> >> I wonder if we can get away without SSE code by saving stat info of
> >> the packed-refs version that we have verified. When we read pack-refs,
> >> if stat info matches, skip check_refname_component(). Assuming that
> >> pack-refs does not change often, of course.
> >
> > Can you elaborate a bit more?
> 
> The first time we read packed_refs, check_refname_format() is called
> in read_packed_refs()->create_ref_entry() as usual. If we find no
> problem, we store packed_refs stat() info in maybe packed_refs.stat.
> Next time we read packed_refs, if packed_refs.stat is there and
> indicates that packed_refs has not changed, we can make
> create_ref_entry() ignore check_refname_format() completely.

I'm confused. Why would we re-open packed-refs at all if the stat information hasn't changed?

read_packed_refs is only called from get_packed_ref_cache, and we only do so if !refs->packed. And refs->packed is only NULL if we haven't read the file yet, or it is stat-dirty.

If that is working as intended, then we should generally only open and read packed-refs once per invocation of git.

-Peff