Re: [PATCH v2 10/13] bash prompt: combine 'git rev-parse' executions
On Tue, Jun 18, 2013 at 02:05:35AM -0400, Jeff King wrote:
> On Tue, Jun 18, 2013 at 04:17:03AM +0200, SZEDER Gábor wrote:
>
> > The whole series speeds up the bash prompt on Windows/MSysGit
> > considerably. Here are some timing results in two scenarios, repeated
> > 10 times:
> >
> > At the top of the work tree, before:
> >
> > $ time for i in {0..9} ; do prompt="$(__git_ps1)" ; done
> >
> > real0m1.716s
> > user0m0.301s
> > sys 0m0.772s
> >
> > After:
> >
> > real0m0.686s
> > user0m0.075s
> > sys 0m0.287s
> >
> > In a subdirectory, during rebase, stash status indicator enabled,
> > before:
> >
> > real0m3.557s
> > user0m0.495s
> > sys 0m1.767s
> >
> > After:
> >
> > real0m0.702s
> > user0m0.045s
> > sys 0m0.409s
>
> Very nice speedup (or perhaps it is a testament to how bad fork() is on
> msys).
Well, it seems it's not just fork() & friends. The latter case on
Linux, before:
$ time for i in {0..99}; do prompt="$(__git_ps1)" ; done
real0m2.819s
user0m0.180s
sys 0m0.272s
After:
real0m0.787s
user0m0.000s
sys 0m0.044s
If you look solely at speedup (Win/MSys: 80%, Linux: 72%), Linux isn't
that much better either, but overall it's about an order of magnitude
faster to begin with (100 repetitions vs. 10).
Btw, it could still be a bit faster in you would care to change your
prompt to run from $PROMPT_COMMAND, because it would avoid that final
$(__git_ps1) command sunstitution, too. But I didn't measured that
because I find the interface awful ;) (Hmm, speaking of which, the
patch reading HEAD might break setups using $PROMPT_COMMAND, because
it might do a simple return without updating $PS1...)
> Reading patches 8 and 9, I can't help but feel that "git status"
> is letting us down a little by making us parse all of this data
> ourselves. In theory, __git_ps1() could just be something like:
>
> eval "$(git status --shell)"
> printf ...
>
> and the heavy lifting could be done in a single C process which does not
> have to worry about fork overhead. But that is quite far from where we
> are now, so while it might be an interesting place to go in the future,
> I do not think such dreams would want to hold up current work.
Yeah, that would be one way to go. It would have the added benefit
that it could support 'core.abbrev' in the non-describable detached
HEAD case without noticable overhead.
OTOH it still requires a command substitution and a git command, so
it's less than ideal. The previous version of this series more than a
year ago did some tricky things to create a prompt without a single
fork(), let alone exec(), e.g. looking for .git directory with bash
builtins, comparing pwd's prefix with path to .git dir to find out
whether inside .git dir, etc. As a result even that
subdir+rebase+stash case could be done in 10ms on Windows. Too bad
that that "inside .git dir" check could misfire on case insensitive
file systems, so we have to do that check with '$(git rev-parse)'.
http://thread.gmane.org/gmane.comp.version-control.git/197432/focus=197450
Gábor
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Re: [PATCH v2 10/13] bash prompt: combine 'git rev-parse' executions
On Tue, Jun 18, 2013 at 04:17:03AM +0200, SZEDER Gábor wrote:
> The whole series speeds up the bash prompt on Windows/MSysGit
> considerably. Here are some timing results in two scenarios, repeated
> 10 times:
>
> At the top of the work tree, before:
>
> $ time for i in {0..9} ; do prompt="$(__git_ps1)" ; done
>
> real0m1.716s
> user0m0.301s
> sys 0m0.772s
>
> After:
>
> real0m0.686s
> user0m0.075s
> sys 0m0.287s
>
> In a subdirectory, during rebase, stash status indicator enabled,
> before:
>
> real0m3.557s
> user0m0.495s
> sys 0m1.767s
>
> After:
>
> real0m0.702s
> user0m0.045s
> sys 0m0.409s
Very nice speedup (or perhaps it is a testament to how bad fork() is on
msys). Reading patches 8 and 9, I can't help but feel that "git status"
is letting us down a little by making us parse all of this data
ourselves. In theory, __git_ps1() could just be something like:
eval "$(git status --shell)"
printf ...
and the heavy lifting could be done in a single C process which does not
have to worry about fork overhead. But that is quite far from where we
are now, so while it might be an interesting place to go in the future,
I do not think such dreams would want to hold up current work.
-Peff
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[PATCH v2 10/13] bash prompt: combine 'git rev-parse' executions
From: SZEDER Gábor
>From the four '$(git rev-parse --)' command substitutions
__git_ps1() executes three in its main code path:
- the first to get the path to the .git directory ('--git-dir'),
- the second to check whether we're inside the .git directory
('--is-inside-git-dir'),
- and the last, depending on the results of the second, either
* to check whether it's a bare repo ('--is-bare-repository'), or
* to check whether inside a work tree ('--is-inside-work-tree').
Naturally, this imposes the overhead of fork()ing three subshells and
fork()+exec()ing three git commands.
Combine these four 'git rev-parse' queries into one and use bash
parameter expansions to parse the combined output, i.e. to separate
the path to the .git directory from the true/false of
'--is-inside-git-dir', etc. This way we can eliminate two of the
three subshells and git commands.
The whole series speeds up the bash prompt on Windows/MSysGit
considerably. Here are some timing results in two scenarios, repeated
10 times:
At the top of the work tree, before:
$ time for i in {0..9} ; do prompt="$(__git_ps1)" ; done
real0m1.716s
user0m0.301s
sys 0m0.772s
After:
real0m0.686s
user0m0.075s
sys 0m0.287s
In a subdirectory, during rebase, stash status indicator enabled,
before:
real0m3.557s
user0m0.495s
sys 0m1.767s
After:
real0m0.702s
user0m0.045s
sys 0m0.409s
Signed-off-by: SZEDER Gábor
---
contrib/completion/git-prompt.sh | 18 +-
1 file changed, 13 insertions(+), 5 deletions(-)
diff --git a/contrib/completion/git-prompt.sh b/contrib/completion/git-prompt.sh
index 10ec6902..b73cebf7 100644
--- a/contrib/completion/git-prompt.sh
+++ b/contrib/completion/git-prompt.sh
@@ -311,8 +311,9 @@ __git_ps1 ()
;;
esac
- local g=
- if ! g="$(git rev-parse --git-dir 2>/dev/null)"; then
+ local repo_info=
+ if ! repo_info="$(git rev-parse --git-dir --is-inside-git-dir \
+ --is-bare-repository --is-inside-work-tree 2>/dev/null)"; then
if [ $pcmode = yes ]; then
#In PC mode PS1 always needs to be set
PS1="$ps1pc_start$ps1pc_end"
@@ -320,6 +321,13 @@ __git_ps1 ()
return
fi
+ local inside_worktree="${repo_info##*$'\n'}"
+ repo_info="${repo_info%$'\n'*}"
+ local bare_repo="${repo_info##*$'\n'}"
+ repo_info="${repo_info%$'\n'*}"
+ local inside_gitdir="${repo_info##*$'\n'}"
+ local g="${repo_info%$'\n'*}"
+
local r=""
local b=""
local step=""
@@ -396,13 +404,13 @@ __git_ps1 ()
local c=""
local p=""
- if [ "true" = "$(git rev-parse --is-inside-git-dir 2>/dev/null)" ]; then
- if [ "true" = "$(git rev-parse --is-bare-repository
2>/dev/null)" ]; then
+ if [ "true" = "$inside_gitdir" ]; then
+ if [ "true" = "$bare_repo" ]; then
c="BARE:"
else
b="GIT_DIR!"
fi
- elif [ "true" = "$(git rev-parse --is-inside-work-tree 2>/dev/null)" ];
then
+ elif [ "true" = "$inside_worktree" ]; then
if [ -n "${GIT_PS1_SHOWDIRTYSTATE-}" ] &&
[ "$(git config --bool bash.showDirtyState)" != "false" ]
then
--
1.8.3.1.487.g8f4672d
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