Re: "submodule foreach" much slower than removed "submodule--helper --list"

From: Jeff King <peff@peff.net>
Date: Oct 17, 2022, 17:46 UTC
Message-ID: <Y02U7611DH6zFsK9@coredump.intra.peff.net>
In-Reply-To: <221017.86h702jsiq.gmgdl@evledraar.gmail.com>

On Mon, Oct 17, 2022 at 06:50:06PM +0200, Ævar Arnfjörð Bjarmason wrote:

Show 6 quoted lines

> Sorry about the slowdown, the removal of "list" was just an in-between
> step to migrating "submodule" to a full built-in.
> 
> I can't reproduce anything like the 8ms v.s. ~600ms difference you note
> here, but for me migrating it to a built-in is around 10% slower with
> "foreach" than the old "list". I wonder what results you get?

I don't think "foreach" can ever be as performant as a bare "list". It inherently is going to do O(n) fork+execs. So it's OK if you have one or two submodules, but not if you have hundreds.

If it treated "echo" as a builtin and served it in-process, it could avoid that extra overhead. But there are so many corner cases there, you'd probably do better to add "list --format" instead.

-Peff