From: Jeff King <peff@peff.net>
Date: Tue, 25 Sep 2007 19:06:40 GMT
Subject: Re: diffcore-rename performance mode
Message-ID: <20070925190640.GA4613@coredump.intra.peff.net>
In-Reply-To: <20070925163843.GA22987@coredump.intra.peff.net>

On Tue, Sep 25, 2007 at 12:38:43PM -0400, Jeff King wrote:

>[...]
>
> What is most confusing is why the 'somefree' case performs so badly,
> since we should just be using the cnt_data. I'll see if gprof can shed

OK, I found the problem. estimate_similarity calls
diff_populate_filespec each time, even if we already have the cnt_data,
which leads to recomputing the blob contents from deltas. Oops.

Fixing this, the correct numbers are:

                 | stock | nofree | old somefree | fixed somefree
-----------------|-----------------------------------------------
user time (s)    | 76.78 | 16.96  | 46.26        | 16.99
peak memory (Kb) | 52300 | 66796  | 59156        | 57328

So now we're at a 4.5x speedup for about 10% extra memory usage. Patch
will follow.

-Peff