Subject: Re: [PATCH] Enable parallelism in git submodule update.

From: Jens Lehmann <[email-masked]>
Date: Sat, 03 Nov 2012 16:42:10 +0100

Am 30.10.2012 19:11, schrieb Stefan Zager:
> This is a refresh of a conversation from a couple of months ago.
> 
> I didn't try to implement all the desired features (e.g., smart logic
> for passing a -j parameter to recursive submodule invocations), but I
> did address the one issue that Junio insisted on: the code makes a
> best effort to detect whether xargs supports parallel execution on the
> host platform, and if it doesn't, then it prints a warning and falls
> back to serial execution.

I suspect not passing on --jobs recursively like you do here is the
right thing to do, as that would give exponential growth of jobs with
recursion depth, which makes no sense to me.

A still unsolved issue is the unstructured output from the different
update jobs. It'll be hard (if not impossible) to see in what submodule
which update took place (or failed). I think we should have a solution
for that too (maybe one of those Heiko mentioned or something as simple
as implying "-q"?).

> Stefan
> 
> On Tue, Oct 30, 2012 at 11:03 AM,  <[email-masked]> wrote:
>> The --jobs parameter may be used to set the degree of per-submodule
>> parallel execution.
>
>> Signed-off-by: Stefan Zager <[email-masked]>
>> ---
>>  Documentation/git-submodule.txt |    8 ++++++-
>>  git-submodule.sh                |   40 ++++++++++++++++++++++++++++++++++++++-
>>  2 files changed, 46 insertions(+), 2 deletions(-)
>>
>> diff --git a/Documentation/git-submodule.txt b/Documentation/git-submodule.txt
>> index b4683bb..cb23ba7 100644
>> --- a/Documentation/git-submodule.txt
>> +++ b/Documentation/git-submodule.txt
>> @@ -14,7 +14,8 @@ SYNOPSIS
>>  'git submodule' [--quiet] status [--cached] [--recursive] [--] [<path>...]
>>  'git submodule' [--quiet] init [--] [<path>...]
>>  'git submodule' [--quiet] update [--init] [-N|--no-fetch] [--rebase]
>> -             [--reference <repository>] [--merge] [--recursive] [--] [<path>...]
>> +             [--reference <repository>] [--merge] [--recursive]
>> +             [-j|--jobs [jobs]] [--] [<path>...]
>>  'git submodule' [--quiet] summary [--cached|--files] [(-n|--summary-limit) <n>]
>>               [commit] [--] [<path>...]
>>  'git submodule' [--quiet] foreach [--recursive] <command>
>> @@ -146,6 +147,11 @@ If the submodule is not yet initialized, and you just want to use the
>>  setting as stored in .gitmodules, you can automatically initialize the
>>  submodule with the `--init` option.
>>  +
>> +By default, each submodule is treated serially.  You may specify a degree of
>> +parallel execution with the --jobs flag.  If a parameter is provided, it is
>> +the maximum number of jobs to run in parallel; without a parameter, all jobs are
>> +run in parallel.
>> ++

The new "--jobs" option should be documented under "OPTIONS", (and maybe
include that "--jobs 0" does the same as "--jobs" alone and that this is
not supported on all platforms).

>>  If `--recursive` is specified, this command will recurse into the
>>  registered submodules, and update any nested submodules within.
>>  +
>> diff --git a/git-submodule.sh b/git-submodule.sh
>> index ab6b110..60a5f96 100755
>> --- a/git-submodule.sh
>> +++ b/git-submodule.sh
>> @@ -8,7 +8,7 @@ dashless=$(basename "$0" | sed -e 's/-/ /')
>>  USAGE="[--quiet] add [-b branch] [-f|--force] [--reference <repository>] [--] <repository> [<path>]
>>     or: $dashless [--quiet] status [--cached] [--recursive] [--] [<path>...]
>>     or: $dashless [--quiet] init [--] [<path>...]
>> -   or: $dashless [--quiet] update [--init] [-N|--no-fetch] [-f|--force] [--rebase] [--reference <repository>] [--merge] [--recursive] [--] [<path>...]
>> +   or: $dashless [--quiet] update [--init] [-N|--no-fetch] [-f|--force] [--rebase] [--reference <repository>] [--merge] [--recursive] [-j|--jobs [jobs]] [--] [<path>...]
>>     or: $dashless [--quiet] summary [--cached|--files] [--summary-limit <n>] [commit] [--] [<path>...]
>>     or: $dashless [--quiet] foreach [--recursive] <command>
>>     or: $dashless [--quiet] sync [--] [<path>...]"
>> @@ -500,6 +500,7 @@ cmd_update()
>>  {
>>         # parse $args after "submodule ... update".
>>         orig_flags=
>> +       jobs="1"
>>         while test $# -ne 0
>>         do
>>                 case "$1" in
>> @@ -518,6 +519,20 @@ cmd_update()
>>                 -r|--rebase)
>>                         update="rebase"
>>                         ;;
>> +               -j|--jobs)
>> +                       case "$2" in
>> +                       ''|-*)
>> +                               jobs="0"
>> +                               ;;
>> +                       *)
>> +                               jobs="$2"
>> +                               shift
>> +                               ;;
>> +                       esac
>> +                       # Don't preserve this arg.
>> +                       shift
>> +                       continue
>> +                       ;;
>>                 --reference)
>>                         case "$2" in '') usage ;; esac
>>                         reference="--reference=$2"
>> @@ -551,11 +566,34 @@ cmd_update()
>>                 shift
>>         done
>>
>> +       # Correctly handle the case where '-q' came before 'update' on the command line.
>> +       if test -n "$GIT_QUIET"
>> +       then
>> +               orig_flags="$orig_flags -q"
>> +       fi
>> +
>>         if test -n "$init"
>>         then
>>                 cmd_init "--" "$@" || return
>>         fi
>>
>> +       if test "$jobs" != 1
>> +       then
>> +               if ( echo test | xargs -P "$jobs" true 2>/dev/null )
>> +               then
>> +                       if ( echo test | xargs --max-lines=1 true 2>/dev/null ); then
>> +                               max_lines="--max-lines=1"
>> +                       else
>> +                               max_lines="-L 1"
>> +                       fi
>> +                       module_list "$@" | awk '{print $4}' |
>> +                       xargs $max_lines -P "$jobs" git submodule update $orig_flags
>> +                       return
>> +               else
>> +                       echo "Warn: parallel execution is not supported on this platform."
>> +               fi
>> +       fi
>> +
>>         cloned_modules=
>>         module_list "$@" | {
>>         err=
>> --
>> 1.7.7.3
>>
> --
> To unsubscribe from this list: send the line "unsubscribe git" in
> the body of a message to [email-masked]
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>