linux-kernel - Re: [PATCH 1/2] sched: INIT_PREEMPT

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Message-Id: <1247241066.7529.50.camel@twins>
Date:	Fri, 10 Jul 2009 17:51:06 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Valdis.Kletnieks@...edu
Cc:	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Matt Mackall <mpm@...enic.com>,
	Anton Vorontsov <avorontsov@...mvista.com>,
	Andrew Morton <akpm@...ux-foundation.org>, oleg@...hat.com,
	mingo@...e.hu, tony.luck@...el.com, rth@...ddle.net,
	geert@...ux-m68k.org
Subject: Re: [PATCH 1/2] sched: INIT_PREEMPT_COUNT

On Fri, 2009-07-10 at 11:42 -0400, Valdis.Kletnieks@...edu wrote:
> On Fri, 10 Jul 2009 14:57:56 +0200, Peter Zijlstra said:
> 
> > +/*
> > + * Disable preemption until the scheduler is running.
> > + * Reset by start_kernel()->sched_init()->init_idle().
> > + */
> > +#define INIT_PREEMPT_COUNT	(1)
> > +
> 
> I had to look at this for quite some time before it sank in that it wasn't
> a reset of a #define, or a reset of (1) (anybody else remember changing the
> value of '5' in a Fortran program?).  Especially when stuck in with a bunch
> of cputimer defines. Would have taken even longer if I was looking in sched.h
> for something and not looking at this patch at the same time.
> 
> Can we fix this comment to mention it's thread_info.preempt_count that
> needs the reset?

Something along the lines of the below?

---
Index: linux-2.6/include/linux/sched.h
===================================================================
--- linux-2.6.orig/include/linux/sched.h
+++ linux-2.6/include/linux/sched.h
@@ -502,7 +502,9 @@ struct task_cputime {
 
 /*
  * Disable preemption until the scheduler is running.
- * Reset by start_kernel()->sched_init()->init_idle().
+ *
+ * We reset this initial offset of init_thread_info.preempt_count in:
+ *     start_kernel()->sched_init()->init_idle().
  */
 #define INIT_PREEMPT_COUNT	(1)
 


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