linux-kernel - Re: sched_yield: delete sysctl_sched_compat

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Message-ID: <20071129185144.209108dd@laptopd505.fenrus.org>
Date:	Thu, 29 Nov 2007 18:51:44 -0800
From:	Arjan van de Ven <arjan@...radead.org>
To:	Nick Piggin <nickpiggin@...oo.com.au>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>, mingo@...e.hu,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: sched_yield: delete sysctl_sched_compat_yield

On Fri, 30 Nov 2007 13:46:22 +1100
Nick Piggin <nickpiggin@...oo.com.au> wrote:

> > Todays kernel has a different behavior somewhat (and before people
> > scream "regression"; sched_yield() behavior isn't really specified
> > and doesn't make any sense at all, whatever you get is what you
> > get.... it's pretty much an insane defacto behavior that is
> > incredibly tied to which decisions the scheduler makes how, and no
> > app can depend on that
> 
> It is a performance regression. Is there any reason *not* to use the
> "compat" yield by default? As you say, for SCHED_OTHER tasks, yield
> can do almost anything. We may as well do something that isn't a
> regression..

it just makes OTHER tests/benchmarks regress.... this is one of those
things where you just can't win.

> 
> 
> > in any way. In fact, I've proposed to make sched_yield() just do an
> > msleep(1)... that'd be closer to what sched_yield is supposed to do
> > standard wise than any of the current behaviors .... ;_
> 
> What makes you say that? IIRC of all the things that sched_yeild can
> do, it is not allowed to block. So this is about the only thing that
> will break the standard...

sched_yield OF COURSE can block.. it's a schedule call after all!



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