linux-kernel - Re: [PATCH] convert cnt32_to

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Message-ID: <alpine.DEB.1.10.0811112012190.12838@gandalf.stny.rr.com>
Date:	Tue, 11 Nov 2008 20:13:45 -0500 (EST)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
cc:	David Howells <dhowells@...hat.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Nicolas Pitre <nico@....org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	torvalds@...ux-foundation.org, rmk+lkml@....linux.org.uk,
	mingo@...e.hu, linux-kernel@...r.kernel.org, ralf@...ux-mips.org,
	benh@...nel.crashing.org, paulus@...ba.org, davem@...emloft.net,
	mingo@...hat.com, tglx@...utronix.de, linux-arch@...r.kernel.org
Subject: Re: [PATCH] convert cnt32_to_63 to inline


On Tue, 11 Nov 2008, Peter Zijlstra wrote:

> On Tue, 2008-11-11 at 22:31 +0000, David Howells wrote:
> > Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca> wrote:
> > 
> > > @@ -52,18 +57,22 @@ unsigned long long sched_clock(void)
> > > ...
> > > +	preempt_disable_notrace();
> > 
> > Please, no!  sched_clock() is called with preemption or interrupts disabled
> > everywhere except from some debugging code (lock tracing IIRC).  If you need
> > to insert this preemption disablement somewhere, please insert it there.  At
> > least then sched_clock() will be called consistently.
> 
> Agreed. You could do a WARN_ON(!in_atomic); in sched_clock() depending
> on DEBUG_PREEMPT or something to ensure this.

It would also be nice if this requirement (calling sched_clock with 
preemption disabled) was documented somewhere more obvious.

Doing as Peter suggested, adding a WARN_ON and documenting that this must 
be called with preemption disabled, would be nice.

-- Steve

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