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Date: Thu, 1 Jul 2004 14:06:24 +0200
From: Ingo Molnar <mingo@elte.hu>
To: "Povolotsky, Alexander" <Alexander.Povolotsky@marconi.com>
Cc: "'linux-kernel@vger.kernel.org'" <linux-kernel@vger.kernel.org>,
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       "'Tigran Aivazian'" <tigran@veritas.com>,
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Subject: Re: Linux scheduler (scheduling) questions vs threads
Message-ID: <20040701120624.GA24295@elte.hu>
References: <313680C9A886D511A06000204840E1CF08F42FBC@whq-msgusr-02.pit.comms.marconi.com>
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* 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 doesnt 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.

	Ingo