# Clocksource tsc unstable [solved]

## jlward4th

I am using gentoo-sources-2.6.21-r2 and trying to have a tickless system.  But it doesn't seem to be working.  I get these messages in dmesg:

```
Intel machine check architecture supported.

Intel machine check reporting enabled on CPU#1.

CPU1: Intel(R) Core(TM)2 CPU         T7600  @ 2.33GHz stepping 06

Total of 2 processors activated (9314.91 BogoMIPS).

ENABLING IO-APIC IRQs

..TIMER: vector=0x31 apic1=0 pin1=2 apic2=-1 pin2=-1

checking TSC synchronization [CPU#0 -> CPU#1]:

Measured 720048 cycles TSC warp between CPUs, turning off TSC clock.

Brought up 2 CPUs

migration_cost=8000
```

and

```
Clocksource tsc unstable (delta = -303968304 ns)
```

Any ideas on why my tsc is unstable?  I have a T60p machine.  Thanks in advance.

-JamesLast edited by jlward4th on Sat Jun 02, 2007 7:31 pm; edited 1 time in total

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## micmac

Why do you think "tickless" doesn't work? Nothing in your logs suggests that.

Anyway, tsc is one of multiple clock sources. For CPUs that change frequency tsc isn't reliable, so another clocksource is used. You can check the available clocksources in /sys/devices/system/clocksource/clocksourceX/available_clocksource and the currently used clocksource in /sys/devices/system/clocksource/clocksourceX/current_clocksource

You should have googled a bit before spreading FUD. There's prolly a wikipedia article about tsc as well.

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## jlward4th

I had searched Google for "Clocksource tsc unstable" and didn't seem to find much that helped.  But your post is very helpful.  Thanks!

My clocksource info from /sys is:

```
jamesw@dos ~ $ sudo cat /sys/devices/system/clocksource/clocksource0/available_clocksource 

hpet acpi_pm jiffies tsc 

jamesw@dos ~ $ sudo cat /sys/devices/system/clocksource/clocksource0/current_clocksource 

hpet
```

When I tried to switch to the tsc clocksource my computer hung.

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## micmac

 *jlward4th wrote:*   

> 
> 
> When I tried to switch to the tsc clocksource my computer hung.

 

Just don't. Why would you? HPET is fine and works with mobile CPUs. Don't bother with this clock stuff. The kernel will pick the best available clocksource for your system. The kernel is picky enough :-)

You can check that "tickless" is working with "vmstat 1". "System in" should be ~0 when your computer is really idle. To get to that state you'll probably have to stop HAL (~20 interrupts/s here) and your network adapter [~100 interrupts/s here (noisy network)].

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## jlward4th

Thanks again.  That's great info.

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## Braempje

I'm having the same problem. I switched from gentoo-sources 2.6.18 to 2.6.22 and now I get errors while booting like mentioned at kerneltrap. I just configured a NO_HZ kernel on a Pentium-M, with CPU frequency scaling. How can I resolve this? 

I tried to resolve this with a kernel entry in grub like this:

```
title  Gentoo Linux 2.6.22

root (hd0,5)

kernel /boot/kernel-gentoo-2.6.22 root=/dev/sda8 clocksource=acpi_pm
```

But the problem persists. Any ideas?

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