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

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Date:	Sat, 8 Dec 2007 11:50:50 +1100
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Stefano Brivio <stefano.brivio@...imi.it>,
	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

On Saturday 08 December 2007 03:48, Nick Piggin wrote:
> On Friday 07 December 2007 22:17, Ingo Molnar wrote:
> > * Nick Piggin <nickpiggin@...oo.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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