|author||Jonathan Tan <firstname.lastname@example.org>||Tue Sep 08 12:48:35 2020 -0700|
|committer||Junio C Hamano <email@example.com>||Tue Sep 08 15:52:17 2020 -0700|
index-pack: make quantum of work smaller Currently, when index-pack resolves deltas, it does not split up delta trees into threads: each delta base root (an object that is not a REF_DELTA or OFS_DELTA) can go into its own thread, but all deltas on that root (direct or indirect) are processed in the same thread. This is a problem when a repository contains a large text file (thus, delta-able) that is modified many times - delta resolution time during fetching is dominated by processing the deltas corresponding to that text file. This patch contains a solution to that. When cloning using git -c core.deltabasecachelimit=1g clone \ https://fuchsia.googlesource.com/third_party/vulkan-cts on my laptop, clone time improved from 3m2s to 2m5s (using 3 threads, which is the default). The solution is to have a global work stack. This stack contains delta bases (objects, whether appearing directly in the packfile or generated by delta resolution, that themselves have delta children) that need to be processed; whenever a thread needs work, it peeks at the top of the stack and processes its next unprocessed child. If a thread finds the stack empty, it will look for more delta base roots to push on the stack instead. The main weakness of having a global work stack is that more time is spent in the mutex, but profiling has shown that most time is spent in the resolution of the deltas themselves, so this shouldn't be an issue in practice. In any case, experimentation (as described in the clone command above) shows that this patch is a net improvement. Signed-off-by: Jonathan Tan <firstname.lastname@example.org> Signed-off-by: Junio C Hamano <email@example.com>
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 firstname.lastname@example.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 email@example.com. 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 firstname.lastname@example.org.
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):