gngjeg@gmail.com wrote:
> I would like to apoligize if this question is being posted to the
> wrong group.
>
> I would like to know what is the most bullet-proof way to determine
> what clock source is the Linux kernel using. Normally, I dod this
> making use of "dmesg" as the text below shows.
>
> [joseg@dev03 proc]$ dmesg | grep time.c
> time.c: Using 3.579545 MHz PM timer.
> time.c: Detected 2599.956 MHz processor.
> time.c: Using PM based timekeeping.
> [joseg@dev03 proc]$
>
> [joseg@prod03 ~]$ dmesg | grep time.c
> time.c: Using 1.193182 MHz PIT timer.
> time.c: Detected 2599.994 MHz processor.
> time.c: Using PIT/TSC based timekeeping.
> [joseg@prod03 ~]$
>
> The issue with relying on "dmesg" is that eventually, the message
> buffer might get over written on very busy servers or servers that
> have been up for a very long time.
>
> There is another way that I can use to check for the source, and that
> is by looking at "/proc/cmdline" as the text shows below.
>
> [joseg@prod03 ~]$ cat /proc/cmdline
> ro root=LABEL=/ rhgb quiet nohpet nopmtimer console=tty0
> [joseg@prod03 ~]
>
> However, not all systems will have the clock source clearly defined on
> the kernel boot options under your /boot/grub/menu.lst file. The text
> below shows a systems which do not specify which clock source the
> kernel is supposed to pick.
>
> [joseg@dev03 ~]$ cat /proc/cmdline
> ro root=LABEL=/ rhgb quiet console=tty0
> [joseg@dev03 ~]$
>
> There is some heuristics built into the kernel (time.c) which will
> pick one of the available time or clock sources based on what it is
> available to the system at boot time and what is enabled/disabled in
> the BIOS.
>
> So, is there a way that will help someone that might not have access
> to boot time messages or access to a boot.log to make an accurate
> determination as to which clock source a particular system is running?
>
> Thanks in advance.
>

Using kernel 2.6.23:

ls /sys/devices/system/clocksource/clocksource0/
available_clocksource current_clocksource

cat /sys/devices/system/clocksource/clocksource0/*
acpi_pm pit jiffies tsc
acpi_pm

Jerry