From: Stephen Leake <stephen_leake@stephe-leake.org>
To: Eli Zaretskii <eliz@gnu.org>
Cc: 18626@debbugs.gnu.org
Subject: bug#18626: 24.3.94; communication with subprocess is slow
Date: Fri, 10 Oct 2014 03:07:02 -0500 [thread overview]
Message-ID: <85lhoouz4p.fsf@stephe-leake.org> (raw)
In-Reply-To: <837g0ak6rb.fsf@gnu.org> (Eli Zaretskii's message of "Wed, 08 Oct 2014 16:53:12 +0300")
Eli Zaretskii <eliz@gnu.org> writes:
>> From: Stephen Leake <stephen_leake@stephe-leake.org>
>> Cc: 18626@debbugs.gnu.org
>> Date: Wed, 08 Oct 2014 08:29:59 -0500
>>
>> The cause for this is the Sleep in _sys_read_ahead in w32.c. This is
>> called from reader_thread after the wait for a single char read
>> succeeds. The default wait is 50 ms, set by the elisp variable
>> w32-pipe-read-delay. Setting that to 0 gives:
>>
>> (pipe-torture-read "/Projects/emacs/emacs-24.3.94/src/xdisp.c")
>> 0.180000, 0.095000
>>
>> only a factor of 2 slower than command-line cat.
>>
>> w32-pipe-read-delay is a global variable. The comment in _sys_read_ahead
>> says there are problems with subprocess interaction when setting this to
>> 0 on some systems. If that is still true, we may need to change this to
>> a per-subprocess setting.
>>
>> In my real application, let-binding w32-pipe-read-delay for a short time
>> is possible, and a reasonable workaround.
>
> I think I will set that to -1, on the trunk, except on Windows 9X
> systems. That should cause the reader thread yield its time slice
> before returning. Can you see how this affects your use case?
That has essentially no effect when running on a multi-core machine; the
subprocess is scheduled separately.
> As for the effect of this on non-Windows 9X systems, I don't see the
> problem described in the comment with the "dir" command on Windows XP
> when I set this variable's value to zero. And running DOS programs
> from a w32 Emacs is much less probable use case these days, what with
> the proliferation of 64-bit Windows systems that don't have a DOS
> emulator. So I think we can safely make this value zero or -1 on
> modern systems.
Ok.
> Thanks for tracking this down.
You're welcome. Thanks for your work on Emacs for Windows!
--
-- Stephe
next prev parent reply other threads:[~2014-10-10 8:07 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-10-04 6:47 bug#18626: 24.3.94; communication with subprocess is slow stephen_leake
2014-10-04 8:07 ` Eli Zaretskii
2014-10-05 13:20 ` Stephen Leake
2014-10-05 13:41 ` Stephen Leake
2014-10-05 14:43 ` Eli Zaretskii
2014-10-05 18:19 ` Stephen Leake
2014-10-04 8:11 ` Stephen Leake
2014-10-04 8:32 ` Eli Zaretskii
2014-10-04 22:29 ` Stefan Monnier
2014-10-05 2:46 ` Eli Zaretskii
2014-10-05 13:34 ` Stephen Leake
2014-10-05 14:40 ` Eli Zaretskii
2014-10-05 18:25 ` Stephen Leake
2014-10-05 19:04 ` Eli Zaretskii
2014-10-08 13:29 ` Stephen Leake
2014-10-08 13:53 ` Eli Zaretskii
2014-10-10 8:07 ` Stephen Leake [this message]
2014-10-10 9:13 ` Eli Zaretskii
2014-10-10 8:47 ` Stephen Leake
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