Re: vc-dir operation is very slow on large git repositories in Emacs 26.1

[Eli Zaretskii]

> From: Alex Harsanyi <address@hidden>
> Date: Fri, 22 Jun 2018 20:46:59 +0800
> Cc: address@hidden
> 
> > Does it help to set w32-pipe-buffer-size to some large value, like
> > 16384, and/or decrease w32-pipe-read-delay?
> 
> If I set w32-pipe-read-delay to 0 the speed improvement is
> significant.  On top of that, there is an additional speed
> improvement if I set w32-pipe-buffer-size to 16384

Can you show numbers for these speedups, and compare the times with
Emacs 25.  It would also be useful if you show times with different
values of these, so that the optimal values could be chosen.

I'd be also interested in the timings with the larger repository.

> I will use both these values in my init file.

I recommend against using non-default values globally, as it will bite
you elsewhere.  Emacs has many different use cases wrt running async
subprocesses, and in most of them, the amount of produced output is
quite small, or is received in relatively small chunks.  The defaults
are set to provide reasonable performance and responsiveness in those
case, and shouldn't be changed just because this one use case needs
different values.

What we should do instead is bind these to non-default values in the
vc-git command that produces a lot of output that needs to be read as
quickly as possible.

> Out of curiosity, Eli, since you mentioned that there is no
> performance impact for vc-dir on your system, what values do you
> use for these two variables?

I didn't change the defaults, and the above should explain why.

Thanks.