Messages in this thread | | | From | "Povolotsky, Alexander" <> | Subject | Maximum frequency of re-scheduling (minimum time quantum) questio n | Date | Mon, 5 Jul 2004 04:13:08 -0400 |
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Hello,
In Linux 2.6 kernel, configured with SCHED_RR, - could rescheduling be set to be attempted (and executed when appropriate) at EVERY CLOCK TICK, thus allowing the "other" process/thread (if available and ready at the moment) with the higher (highest at that time) priority or, otherwise, with the same priority (the "next" process/thread in the same Round Robin queue, from which the "current" process/thread was "picked" ) to preempt the "current" process/thread ?
If EVERY CLOCK TICK is not conceptually possible (please note, that I am not claiming that frequent rescheduling is "good", I am just asking to what measure it is possible ...) - then what is the minimum "rescheduling" time quantum (measured in clock ticks) is settable/possible ?
What is the default value (which I presume was chosen as "optimal" ?) ?
Thanks, Best Regards, Alex Povolotsky -----Original Message----- From: Ingo Molnar [mailto:mingo@elte.hu] Sent: Thursday, July 01, 2004 8:06 AM To: Povolotsky, Alexander Cc: 'linux-kernel@vger.kernel.org'; 'rml@tech9.net'; 'akpm@osdl.org'; 'Con Kolivas'; 'Kevin P. Dankwardt'; 'Oliver Neukum'; 'Felipe Alfaro Solana'; 'Tigran Aivazian'; 'corbet@lwn.net' Subject: Re: Linux scheduler (scheduling) questions vs threads
* Povolotsky, Alexander <Alexander.Povolotsky@marconi.com> wrote:
> Sorry for bothering and annoying everyone on this list again with additional > questions ... > > Let assume there is one (and only one) application (user space ) process > running on the Linux 2.6 - with multiple threads within it, created via > "clone" (this happens, I presume, for example, if one uses Monta Vista > library for porting PSOS to Linux). > > What scheduling policies those threads (within the same process) will be > governed by (if any )?
in Linux there's no difference between the scheduling of 'threads' and 'processes'. Both are internally a 'task'. If two tasks share the same MM (this is possible via the use of clone()) then they are called threads. If a task has its own MM (normally created via fork()) then it's called a process - but the scheduler doesn't care.
so the normal Linux scheduling policy applies to 'threads' too. Fully preemptable, SCHED_NORMAL by default, or SCHED_FIFO/SCHED_RR if you set it. The priority (or rt_priority) can be set per-task as well. Newly created threads/processes may inherit (or not) the policy of the parent, this largely depends on the library implementation.
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