Re: [PATCH] scheduler: fix x86 regression in native_sched_clock

[Nick Piggin]

On Friday 07 December 2007 19:45, Ingo Molnar wrote:
> * Stefano Brivio <stefano.brivio@xxxxxxxxx> wrote:
> > This patch fixes a regression introduced by:
> >
> > commit bb29ab26863c022743143f27956cc0ca362f258c
> > Author: Ingo Molnar <mingo@xxxxxxx>
> > Date:   Mon Jul 9 18:51:59 2007 +0200
> >
> > This caused the jiffies counter to leap back and forth on cpufreq
> > changes on my x86 box. I'd say that we can't always assume that TSC
> > does "small errors" only, when marked unstable. On cpufreq changes
> > these errors can be huge.
>
> 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?

My patch should fix the worst cpufreq sched_clock jumping issue
I think.
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