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

[Eli Zaretskii <eliz@gnu.org>]

> From: Bastian Beischer <bastian.beischer@rwth-aachen.de>
> Date: Mon, 25 Jun 2018 17:44:21 +0200
> Cc: Alex Harsanyi <alexharsanyi@gmail.com>, Emacs-Devel <emacs-devel@gnu.org>
> 
> I agree with all of this, but the point is that _if_ with 50 msec
> delay the buffer get's filled completely, we should assume that a
> buffer twice as large woud also get filled completely, provided that
> the input rate is near infinite. I think that assumption is valid
> because the total time is linear with the delay down to delays of
> order 5 msec at least. That should result in a data rate which is
> twice as large. Therefore I don't understand how the timing can be
> independent of the buffer size.

For small enough buffer sizes (32KB etc.), 50 msec is an eternity, I
think.  AFAIR, modern versions of Windows read/write data in 64KB
chunks.

> Looking at commit 58a622d473112f8ff5b4bdb3e49bc6573dfd3404 (where you
> introduced w32-pipe-buffer-size) I can see a code path that results in
> resetting the buffer size to 4 KB. Maybe that get's taken?

Only if the GetNamedPipeInfo call fails, which I don't expect to
happen (and should be easy to verify by running Emacs under a
debugger, where the debug message in that case should be visible).