[patch 00/16] arm: Replace arm sched_clock by clocksource based sched_clock

Thomas Gleixner
2011-04-29T21:57:47Z

On Fri, 29 Apr 2011, Linus Walleij wrote:

> 2011/4/29 Thomas Gleixner <tglx@linutronix.de>:
> > On Fri, 29 Apr 2011, Tony Lindgren wrote:
> >> What about PRINTK_TIME? I think that uses sched_clock right from the
> >> start.
> >
> > Right, but where is the problem ? A few time stamps with jiffies
> > resolution and then the finegrained ones.
>
> Jonas ?berg has this pending patch that we call "boot time recorder".
> What it does is basically start a free running timer before the
> kernel is booted, e.g. in U-boot or even in the ROM of your
> machine if you can.
>
> If we need more finegrained sched_clock() before the
> clocksource is up, a good approach would be to utilize
> something like that for sched_clock up to that point, plus
> it has the upside that [0.000000] is as close to electrical
> power-on as possible.

Well, you can read out that value at the point the clocksource gets
installed so you have the time spent up to that point without adding
another facility, level of indirection ...

Thanks,

tglx