From: David.Kastrup@t-online.de (David Kastrup)
Subject: Re: Any idea about what makes Emacs slow reading on pipes?
Date: 19 May 2003 10:24:47 +0200 [thread overview]
Message-ID: <x57k8ne434.fsf@lola.goethe.zz> (raw)
In-Reply-To: <84r86vz8z0.fsf@lucy.is.informatik.uni-duisburg.de>
kai.grossjohann@gmx.net (Kai Großjohann) writes:
> David.Kastrup@t-online.de (David Kastrup) writes:
>
> > Richard Stallman <rms@gnu.org> writes:
> >
> >> We might change it so that, after stashing the stuff in a
> >> buffer, Emacs looks again if more data is available from the
> >> same process.
> >
> > More data will not be available from the same process, since the
> > process has not had any chance to get CPU time again for
> > generating more data. We are talking about a uniprocessor machine
> > here.
>
> I'm not familiar with the internals of Unix (-like) systems, but
> maybe it is possible to "look" in such a way that the scheduler has
> a chance to do its thing. For example, say that using select(2)
> causes the scheduler to run, then we might "look" using select(2).
The scheduler _has_ already made its decision, and the decision is to
have Emacs run rather than the output generating process.
There are various reasons: Emacs has been waiting on that pipe for a
longer time, so it is judged an "interactive program" and not a
calculating one. It gets an interactivity bonus and gets scheduled
immediately when available.
This interactivity bonus gets lower while busy processing continues.
That is the reason that after a while, a few larger packets make it
through.
> Hm. But this might make Emacs quite a bit slower. So maybe it is a
> good idea to only look twice if little data has been received. If a
> lot of data has been read, then we can just process that
> immediately.
The only way to yield is to actually and voluntarily call a delay.
This should only be done when there is reason to suspect it might be
worth a try, namely when we find ourselves repeatedly working on
small packets in fast succession. Emacs should just refuse to call a
process filter too fast twice in a row unless it has stuffed the
buffer sufficiently, and it should have a very fast path when it
decides not to run the process filter yet.
Perhaps a better scheme would be to use _blocking_ reads with the full
buffer length and a timeout instead when something is available. When
the blocking read fails, get just what is there.
--
David Kastrup, Kriemhildstr. 15, 44793 Bochum
next prev parent reply other threads:[~2003-05-19 8:24 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-05-16 13:08 Any idea about what makes Emacs slow reading on pipes? David Kastrup
2003-05-16 13:55 ` Andreas Schwab
2003-05-16 17:18 ` Kevin Rodgers
2003-05-16 17:34 ` David Kastrup
2003-05-16 18:38 ` Kevin Rodgers
2003-05-16 18:49 ` David Kastrup
2003-05-16 17:48 ` Jan D.
2003-05-16 18:38 ` David Kastrup
2003-05-16 20:23 ` Jan D.
2003-05-16 21:00 ` Andreas Schwab
2003-05-16 23:17 ` Satyaki Das
2003-05-17 1:50 ` Kim F. Storm
2003-05-17 0:34 ` David Kastrup
2003-05-18 0:31 ` Kim F. Storm
2003-05-17 23:07 ` Stefan Monnier
2003-05-17 23:39 ` David Kastrup
2003-05-18 2:09 ` Stefan Monnier
2003-05-18 8:45 ` Kai Großjohann
2003-05-18 10:12 ` David Kastrup
2003-05-18 19:04 ` Richard Stallman
2003-05-18 19:46 ` David Kastrup
2003-05-19 7:33 ` Kai Großjohann
2003-05-19 8:24 ` David Kastrup [this message]
2003-05-18 8:46 ` Kai Großjohann
2003-05-18 10:03 ` David Kastrup
2003-05-18 15:09 ` Kai Großjohann
2003-05-18 15:36 ` David Kastrup
2003-05-18 15:50 ` Kai Großjohann
2003-05-18 16:28 ` David Kastrup
2003-05-19 7:26 ` Kai Großjohann
2003-05-19 8:09 ` David Kastrup
2003-05-18 19:03 ` Richard Stallman
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