__git_ps1() is usually added to the prompt inside a command
substitution, imposing the overhead of fork()ing a subshell. Using
__git_ps1() for $PROMPT_COMMAND is slightly faster, because it avoids
that command substitution.
Mention this in the comments about setting up the git prompt.
The whole series speeds up the bash prompt on Windows/MSysGit
considerably. Here are some timing results in three scenarios, each
repeated 10 times:
At the top of the work tree, before:
$ time for i in {0..9} ; do prompt="$(__git_ps1)" ; done
real 0m1.716s
user 0m0.301s
sys 0m0.772s
After:
real 0m0.687s
user 0m0.075s
sys 0m0.396s
After, from $PROMPT_COMMAND:
$ time for i in {0..9} ; do __git_ps1 '\h:\w' '$ ' ; done
real 0m0.546s
user 0m0.075s
sys 0m0.181s
At the top of the work tree, detached head, before:
real 0m2.574s
user 0m0.376s
sys 0m1.207s
After:
real 0m1.139s
user 0m0.151s
sys 0m0.500s
After, from $PROMPT_COMMAND:
real 0m1.030s
user 0m0.245s
sys 0m0.336s
In a subdirectory, during rebase, stash status indicator enabled,
before:
real 0m3.557s
user 0m0.495s
sys 0m1.767s
After:
real 0m0.717s
user 0m0.120s
sys 0m0.300s
After, from $PROMPT_COMMAND:
real 0m0.577s
user 0m0.047s
sys 0m0.258s
On Linux the speedup ratio is comparable to Windows, but overall it
was about an order of magnitude faster to begin with. The last case
from above, repeated 100 times, before:
$ time for i in {0..99} ; do prompt="$(__git_ps1)" ; done
real 0m2.806s
user 0m0.180s
sys 0m0.264s
After:
real 0m0.857s
user 0m0.020s
sys 0m0.028s
Signed-off-by: SZEDER Gábor <szeder@ira.uka.de>
a694258457