Re: w32-pipe-read-delay (was: vc-dir operation is very slow on large git repositories in Emacs 26.1)

[Alex Harsanyi <alexharsanyi@gmail.com>]

On 23 Jun 2018, at 9:40 pm, Eli Zaretskii <eliz@gnu.org> wrote:

>> From: Alex Harsanyi <alexharsanyi@gmail.com>
>> Date: Sat, 23 Jun 2018 21:32:24 +0800
>> 
>> Oops, above I meant to say 0.08, not 0.8, here some sequential runs with
>> `w32-pipe-read-delay` set to 0 and `w32-pipe-buffer-size` set to 0:
>> 
>>    time-process: it took 0.08 seconds
>>    time-process: it took 0.14 seconds
>>    time-process: it took 0.09 seconds
>>    time-process: it took 0.14 seconds [2 times]
>>    time-process: it took 0.14 seconds
>>    time-process: it took 0.09 seconds
>>    time-process: it took 0.14 seconds
>>    time-process: it took 0.11 seconds
>>    time-process: it took 0.13 seconds
>>    time-process: it took 0.09 seconds
>>    time-process: it took 0.14 seconds
>>    time-process: it took 0.09 seconds
> 
> I'm confused: w32-pipe-buffer-size is zero by default, so what can we
> learn about it from the above experiment?

Increasing w32-pipe-buffer-size has no effect on the speed of reading from the pipe. I tried several buffer size values, in combination with several read delay values, but only the read delay has an effect. For example, at 50 milliseconds read delay, it takes ~13 seconds to read 1 Mb of data, regardless if the buffer size is set to 0, 4096, 8192 or 16384. 

In one of my previous emails I indicated that increasing the buffer size made things faster, but that was an incorrect test, since I only run the test once, and there is some variation in the timings — this is what I tried to explain in the last email. 

Apologies for the confusion. 

Alex.