Re: [PATCH] pmtmr and PRINTK_TIME timings display

[john stultz <johnstul@us.ibm.com>]

On Thu, 2005-08-04 at 17:23 +0200, Borislav Petkov wrote:
> I get it. Actually, I wasn't very sure whether this is the right solution 
> since my desktop machine uses tsc timer as default while the laptop the 
> pmtmr. I also remember that there was a patch a while ago on lkml which 
> enabled a modifiable behavior for PRINTK_TIME through a /proc interface and 
> kernel boot option but it somehow didn't get accepted. Ok, then, since we 
> keep the jiffies solution across arch's, how can I force the kernel to use 
> tsc for printk timings so that i can see the deltas between the different 
> printk's instead of the jiffies_64 ns value? The Pentium-M Centrino on the 
> laptop evidently supports rdtsc as a msr instruction.

The issue is that there are a number of laptops that do not properly
support cpufreq and additionally newer laptop chips halt their TSC's
when they go into C3 mode. This keeps the TSC from working as a proper
timesource on these systems, and causes the need for alternative
timesources like the ACPI PM timer. 

thanks
-john