* Thomas Gleixner [off-list ref] [110429 14:54]:

On Fri, 29 Apr 2011, Linus Walleij wrote:

quoted

2011/4/29 Thomas Gleixner [off-list ref]:

quoted

On Fri, 29 Apr 2011, Tony Lindgren wrote:

quoted

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 ...

I think the problem here too is that we are calling read_persistent_clock
and sched_clock before they're initialized. So we should default to
jiffies based value before the platform code enables the hardware.

Tony