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

[Alex Harsanyi]

On Mon, Jun 25, 2018 at 7:09 PM, Bastian Beischer
<address@hidden> wrote:
> Hi,
>
> On Mon, Jun 25, 2018 at 12:40 PM, Alex Harsanyi <address@hidden> wrote:

>> So, with a 50 millisecond delay, it takes 83.7 seconds to read the command
>> output and this is reduced to 1.07 seconds when the delay is set to 0.
>
> From these timings it appears that you have been using a 4096 byte
> buffer. The logic is as follows:
>
> Assume that all the delay in the 83.7 seconds is due to 50ms waits,
> one such wait whenever the buffer is full. This is based on the fact
> that you observe a ~proportional slowdown when increasing the
> read-delay. Then this means that the buffer was full 1674 times, which
> means that the buffer size is 6.5 MB / 1674 = 4071 - approx. 4096
> bytes. So the predicted approximate delay for a message of size S is
>
> D = (S / B) * W
>
> where B is the buffer size (4096) and W is the w32-pipe-read-delay
> (0.05 s). Based on that logic it appears that setting
> w32-pipe-buffer-size to 16384 should give you a ~four times smaller
> total delay - especially when w32-pipe-read-delay is 50 ms, for
> example. Unless the OS refuses to provide you with such a buffer size?
>

Setting w32-pipe-buffer-size has no effect on the timings, see my
previous emails about this.   I do not know why.

Alex.