From: stefano.brivio@polimi.it
Message-ID: <20071207122310.maqkoxlb4gsg4ggc@webmail.polimi.it>
Date: Fri, 07 Dec 2007 12:23:10 +0100
To: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Ingo Molnar <mingo@elte.hu>, 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>
Subject: Re: [PATCH] scheduler: fix x86 regression in native_sched_clock
References: <20071207021952.6f0ac922@morte>
	<20071207084559.GA11162@elte.hu>
	<200712072213.06530.nickpiggin@yahoo.com.au>
In-Reply-To: <200712072213.06530.nickpiggin@yahoo.com.au>
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Quoting Nick Piggin <nickpiggin@yahoo.com.au>:

> On Friday 07 December 2007 19:45, Ingo Molnar 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?

I guess so. Definitely, it didn't look like a printk issue. Drivers  
don't read logs, usually. But they got confused anyway (it seems that  
udelay's get scaled or fail or somesuch - I can't test it right now,  
will provide more feedback in a few hours).


--
Ciao
Stefano


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