linux-kernel - Re: [PATCH] scheduler: fix x86 regression in native_sched

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Message-ID: <20071207122310.maqkoxlb4gsg4ggc@webmail.polimi.it>
Date:	Fri, 07 Dec 2007 12:23:10 +0100
From:	stefano.brivio@...imi.it
To:	Nick Piggin <nickpiggin@...oo.com.au>
Cc:	Ingo Molnar <mingo@...e.hu>, Robert Love <rml@...h9.net>,
	linux-kernel@...r.kernel.org, Dave Jones <davej@...hat.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>, Michael Buesch <mb@...sch.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Len Brown <lenb@...nel.org>
Subject: Re: [PATCH] scheduler: fix x86 regression in native_sched_clock

Quoting Nick Piggin <nickpiggin@...oo.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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