linux-kernel - Re: yield API

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Message-ID: <878x6lwndp.fsf@suzuka.mcnaught.org>
Date:	Tue, 02 Oct 2007 11:24:18 -0400
From:	Douglas McNaught <doug@...aught.org>
To:	"linux-os \(Dick Johnson\)" <linux-os@...logic.com>
Cc:	"Ingo Molnar" <mingo@...e.hu>,
	"David Schwartz" <davids@...master.com>,
	<linux-kernel@...r.kernel.org>
Subject: Re: yield API

"linux-os \(Dick Johnson\)" <linux-os@...logic.com> writes:

> Whether or not there is a POSIX definition of sched_yield(),
> there is a need for something that will give up the CPU
> and not busy-wait. There are many control applications
> where state-machines are kept in user-mode code. The code
> waits for an event. It shouldn't be spinning, wasting
> CPU time, when the kernel can be doing file and network
> I/O with the wasted CPU cycles.

These "control applications" would be real-time processes, for which
(AIUI) sched_yield() behavior is completely well-defined and
implemented as such by Linux.  The question here is how useful the
call is for SCHED_OTHER (non-real-time) processes, for which it has no
well-defined semantics.

-Doug
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