1184a95ea2
They were disabled at 53b8d93 ("grep: disable threading in non-worktree
case", 12-12-2011), due to observable performance drops (to the point
that using a single thread would be faster than multiple threads). But
now that zlib inflation can be performed in parallel we can regain the
speedup, so let's re-enable threads in non-worktree grep.
Grepping 'abcd[02]' ("Regex 1") and '(static|extern) (int|double) \*'
("Regex 2") at chromium's repository[1] I got:
Threads | Regex 1 | Regex 2
---------|------------|-----------
1 | 17.2920s | 20.9624s
2 | 9.6512s | 11.3184s
4 | 6.7723s | 7.6268s
8** | 6.2886s | 6.9843s
These are all means of 30 executions after 2 warmup runs. All tests were
executed on an i7-7700HQ (quad-core w/ hyper-threading), 16GB of RAM and
SSD, running Manjaro Linux. But to make sure the optimization also
performs well on HDD, the tests were repeated on another machine with an
i5-4210U (dual-core w/ hyper-threading), 8GB of RAM and HDD (SATA III,
5400 rpm), also running Manjaro Linux:
Threads | Regex 1 | Regex 2
---------|------------|-----------
1 | 18.4035s | 22.5368s
2 | 12.5063s | 14.6409s
4** | 10.9136s | 12.7106s
** Note that in these cases we relied on hyper-threading, and that's
probably why we don't see a big difference in time.
Unfortunately, multithreaded git-grep might be slow in the non-worktree
case when --textconv is used and there're too many text conversions.
Probably the reason for this is that the object read lock is used to
protect fill_textconv() and therefore there is a mutual exclusion
between textconv execution and object reading. Because both are
time-consuming operations, not being able to perform them in parallel
can cause performance drops. To inform the users about this (and other
threading details), let's also add a "NOTES ON THREADS" section to
Documentation/git-grep.txt.
[1]: chromium’s repo at commit 03ae96f (“Add filters testing at DSF=2”,
04-06-2019), after a 'git gc' execution.
Signed-off-by: Matheus Tavares <matheus.bernardino@usp.br>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Git - fast, scalable, distributed revision control system
Git is a fast, scalable, distributed revision control system with an unusually rich command set that provides both high-level operations and full access to internals.
Git is an Open Source project covered by the GNU General Public License version 2 (some parts of it are under different licenses, compatible with the GPLv2). It was originally written by Linus Torvalds with help of a group of hackers around the net.
Please read the file INSTALL for installation instructions.
Many Git online resources are accessible from https://git-scm.com/ including full documentation and Git related tools.
See Documentation/gittutorial.txt to get started, then see
Documentation/giteveryday.txt for a useful minimum set of commands, and
Documentation/git-<commandname>.txt for documentation of each command.
If git has been correctly installed, then the tutorial can also be
read with man gittutorial or git help tutorial, and the
documentation of each command with man git-<commandname> or git help <commandname>.
CVS users may also want to read Documentation/gitcvs-migration.txt
(man gitcvs-migration or git help cvs-migration if git is
installed).
The user discussion and development of Git take place on the Git mailing list -- everyone is welcome to post bug reports, feature requests, comments and patches to git@vger.kernel.org (read Documentation/SubmittingPatches for instructions on patch submission). To subscribe to the list, send an email with just "subscribe git" in the body to majordomo@vger.kernel.org. The mailing list archives are available at https://lore.kernel.org/git/, http://marc.info/?l=git and other archival sites.
Issues which are security relevant should be disclosed privately to the Git Security mailing list git-security@googlegroups.com.
The maintainer frequently sends the "What's cooking" reports that list the current status of various development topics to the mailing list. The discussion following them give a good reference for project status, development direction and remaining tasks.
The name "git" was given by Linus Torvalds when he wrote the very first version. He described the tool as "the stupid content tracker" and the name as (depending on your mood):
- random three-letter combination that is pronounceable, and not actually used by any common UNIX command. The fact that it is a mispronunciation of "get" may or may not be relevant.
- stupid. contemptible and despicable. simple. Take your pick from the dictionary of slang.
- "global information tracker": you're in a good mood, and it actually works for you. Angels sing, and a light suddenly fills the room.
- "goddamn idiotic truckload of sh*t": when it breaks