Re: [PATCH] check_refname_component: Optimize

From: Duy Nguyen <pclouds@gmail.com>
Date: May 29, 2014, 23:43 UTC
Message-ID: <CACsJy8BgriBBWJ6ZzQS8S7p4SUB=bdZHdnUQsyN03g+vtApbxA@mail.gmail.com>
In-Reply-To: <20140529234109.GA28683@sigill.intra.peff.net>

On Fri, May 30, 2014 at 6:41 AM, Jeff King <peff@peff.net> wrote:

Show 18 quoted lines

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

No, not in the same process. In the next run.

Show 9 quoted lines

>
> 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

-- 
Duy