Re: Make the git codebase thread-safe

From: David Kastrup <dak@gnu.org>
Date: Feb 12, 2014, 19:15 UTC
Message-ID: <87ppms87n7.fsf@fencepost.gnu.org>
In-Reply-To: <CAHOQ7J_pg6Nqc5TdU9OA81=d+ZG_JpLFQ5-eFLY3uW8CuAQrUQ@mail.gmail.com>

Stefan Zager <szager@chromium.org> writes:

Show 11 quoted lines

> On Wed, Feb 12, 2014 at 10:50 AM, David Kastrup <dak@gnu.org> wrote:
>
>> Really, give the above patch a try.  I am taking longer to finish it
>> than anticipated (with a lot due to procrastination but that is,
>> unfortunately, a large part of my workflow), and it's cutting into my
>> "paychecks" (voluntary donations which to a good degree depend on timely
>> and nontrivial progress reports for my freely available work on GNU
>> LilyPond).
>
> I will give that a try.  How much of a performance improvement have
> you clocked?

Depends on file type and size. With large files with lots of small changes, performance improvements get more impressive.

Some ugly real-world examples are the Emacs repository, src/xdisp.c (performance improvement about a factor of 3), a large file in the style of /usr/share/dict/words clocking in at a factor of about 5.

Again, that's with an SSD and ext4 filesystem on GNU/Linux, and there are no improvements in system time (I/O) except for patch 4 of the series which helps perhaps 20% or so.

So the benefits of the patch will come into play mostly for big, bad files on Windows: other than that, the I/O time is likely to be the dominant player anyway.

If you have benchmarked the stuff, for annoying cases expect I/O time to go down maybe 10-20%, and user time to drop by a factor of 4. Under GNU/Linux, that makes for a significant overall improvement. On Windows, the payback is likely quite less because of the worse I/O performance. Pity.

-- 
David Kastrup