linux-kernel - Re: sched_yield() on 2.6.25

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Date:	Mon, 9 Jun 2008 08:37:24 +0200
From:	Jakub Jozwicki <jozwicki@...er.pl>
To:	linux-kernel@...r.kernel.org
Cc:	Robert Hancock <hancockr@...w.ca>
Subject: Re: sched_yield() on 2.6.25


> > Is this behavior expected?
>
> The behavior of sched_yield with SCHED_OTHER processes has changed
> several times with Linux over the years, since its behavior is not
> defined by standards, so it's really "whatever the scheduler feels like
> doing". The behavior is only defined with realtime scheduling
> (SCHED_FIFO or SCHED_OTHER).
>
> Generally, it's a mistake to assume specific timing behavior from
> sched_yied for SCHED_OTHER processes.

>From the man sched_yield:

A  process  can  relinquish  the  processor  voluntarily without blocking by
calling sched_yield().  The process will then be moved to the  end  of  the 
queue  for  its static priority and a new process gets to run.

and also IEEE/Open Group:
http://www.opengroup.org/onlinepubs/000095399/functions/sched_yield.html

>>	pthread_mutex_lock(&mutex);
> > 	th = pthread_self();
> > 	if (pthread_equal(th,last_th)) {
> > 	    pthread_mutex_unlock(&mutex);
> > 	    sched_yield();
> > 	    continue;

Here with SCHED_OTHER sched_yield for the first 100-200 times does nothing.
Should the man be updated?

Regards,
Jakub
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