From: Vinzent 'Gadget' Hoefler <nntp-2005-02@t-domaingrabbing.de>
Subject: Re: TRON for AdaOS
Date: Fri, 18 Feb 2005 09:46:21 +0000
Date: 2005-02-18T09:46:21+00:00 [thread overview]
Message-ID: <1681323.f4aX4jHe7e@jellix.jlfencey.com> (raw)
In-Reply-To: wvbrfyzuxmc6.fsf@sun.com
Ole-Hjalmar Kristensen wrote:
> My point is that the task switching overhead itself is very low on
> Linux.
Yes. But such things can change when you apply real-time requirements.
Sometimes it is very surprising to see the difference between an
average-case optimization and a worst-case optimization. ;-)
Well, I searched for it and the context switching times simply seem to
depend on the method used.
<URI:http://trecom.upv.es/articles/NTCC150-4.PDF> states:
|The communication method between the scheduler and the Linux process
|can be done by means of the RT-Linux standard RT-fifos, although a
|shared memory mechanism has also been implemented in order to improve
|efficiency. This method allows the scheduler to improve context
|switches by three milliseconds below the accomplished with the FIFO
|communication.
So indeed here they talking about milliseconds, but with the shared
memory approach this seems to change considerably:
|Some measurements about context switching times in RT-Linux have been
|made in the execution of the previous program. [...] In the case of
|interrupts, this time is very variable, but it can be up to 20
|microseconds in the worst case. [...] In the case of system calls, the
|context switching time is much lower: 8 µs. The scheduler requires
|about 4 microseconds.
So that doesn't sound too bad. ;)
Vinzent.
--
worst case: The wrong assumption there actually is one.
next prev parent reply other threads:[~2005-02-18 9:46 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-02-17 7:31 TRON for AdaOS Marius Amado Alves
2005-02-17 12:50 ` Marin David Condic
2005-02-17 13:37 ` Marius Amado Alves
2005-02-17 14:37 ` Ole-Hjalmar Kristensen
2005-02-17 14:55 ` Vinzent 'Gadget' Hoefler
2005-02-18 9:13 ` Ole-Hjalmar Kristensen
2005-02-18 9:46 ` Vinzent 'Gadget' Hoefler [this message]
2005-02-18 13:20 ` Marin David Condic
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