linux-kernel - Re: [PATCH] cleanup sched

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Date:	Wed, 18 Nov 2009 22:34:38 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Sven-Thorsten Dietrich <sven@...bigcorporation.com>
cc:	Jean Delvare <khali@...ux-fr.org>,
	Leon Woestenberg <leon.woestenberg@...il.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	linux-i2c@...r.kernel.org,
	rt-users <linux-rt-users@...r.kernel.org>,
	"Ben Dooks (embedded platforms)" <ben-linux@...ff.org>,
	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] cleanup sched_yield (sys)call nesting.

On Wed, 18 Nov 2009, Sven-Thorsten Dietrich wrote:

> On Wed, 2009-11-18 at 21:56 +0100, Thomas Gleixner wrote:
> > On Wed, 18 Nov 2009, Sven-Thorsten Dietrich wrote:
> > > On Wed, 2009-11-18 at 17:52 +0100, Jean Delvare wrote:
> > > > On Wed, 18 Nov 2009 17:28:53 +0100, Leon Woestenberg wrote:
> > > > > On Wed, Nov 18, 2009 at 2:05 AM, Alan Cox <alan@...rguk.ukuu.org.uk> wrote:
> > > > > > Our timers are very efficient and some day we will need to make jiffies a
> > > > > > function and stop the timer ticking for best performance. At that point
> > > > > > timers are probably the most efficient way to do much of this.
> > > > >
> > > > > The problem with I2C bitbanged is the stringent timing, we need a way
> > > > > to have fine-grained sleeping
> > > > > mixed with real-time tasks in order to make this work.
> > > > 
> > > > FWIW, the problem that was initially reported has nothing to do with
> > > > this. i2c-algo-bit used mdelay() during transactions, not yield().
> > > > yield() is used only in once place, _between_ transactions attempts.
> > > > There are no strict timing constraints there.
> > > > 
> > > 
> > > I agree that dropping out sched_yield entirely should maybe start by
> > > deprecating / flagging as a warning in sched_rt.c.
> > 
> > Errm, that's unrelated to sched_rt.c. 
> > 
> > yield() in the kernel in general is needs to be deprecated.
> >  
> > > This is just a minimal cleanup I stumbled across while looking at it -
> > > to get away from the uglyness of calling into the syscall interface from
> > > inside the Kernel.
> > 
> > And why exactly is that ugly ?
> 
> Calling from a function returning void into a non-void function and then
> ignoring the return code ?
 
Care to read what I wrote further down ?

>> Which is completely irrelevant because the return code is always 0. 

Thanks,

	tglx
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