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From: Nick Piggin <nickpiggin@yahoo.com.au>
To: Ingo Molnar <mingo@elte.hu>
Subject: Re: [PATCH] scheduler: fix x86 regression in native_sched_clock
Date: Sat, 8 Dec 2007 11:50:50 +1100
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Cc: Stefano Brivio <stefano.brivio@polimi.it>, Robert Love <rml@tech9.net>,
       linux-kernel@vger.kernel.org, Dave Jones <davej@redhat.com>,
       "Rafael J. Wysocki" <rjw@sisk.pl>, Michael Buesch <mb@bu3sch.de>,
       Thomas Gleixner <tglx@linutronix.de>,
       Andrew Morton <akpm@linux-foundation.org>, Len Brown <lenb@kernel.org>
References: <20071207021952.6f0ac922@morte> <20071207111720.GA10543@elte.hu> <200712080348.53117.nickpiggin@yahoo.com.au>
In-Reply-To: <200712080348.53117.nickpiggin@yahoo.com.au>
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On Saturday 08 December 2007 03:48, Nick Piggin wrote:
> On Friday 07 December 2007 22:17, Ingo Molnar wrote:
> > * Nick Piggin <nickpiggin@yahoo.com.au> wrote:
> > > > ah, printk_clock() still uses sched_clock(), not jiffies. So it's
> > > > not the jiffies counter that goes back and forth, it's sched_clock()
> > > > - so this is a printk timestamps anomaly, not related to jiffies. I
> > > > thought we have fixed this bug in the printk code already:
> > > > sched_clock() is a 'raw' interface that should not be used directly
> > > > - the proper interface is cpu_clock(cpu).
> > >
> > > It's a single CPU box, so sched_clock() jumping would still be
> > > problematic, no?
> >
> > sched_clock() is an internal API - the non-jumping API to be used by
> > printk is cpu_clock().
>
> You know why sched_clock jumps when the TSC frequency changes, right?

Ah, hmm, I don't know why I wrote that :)

I guess your patch is fairly complex but it should work if the plan
is to convert all sched_clock users to use cpu_clock eg like lockdep
as well.

So it looks good to me, thanks for fixing this.
--
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