Description of problem:
I am attempting to use the TSC as a clocksource for a RHEL4.7 based KVM guest, and the TSC is declared unstable:

...
kernel: checking TSC synchronization across 4 CPUs: passed.
...

kernel: Losing too many ticks!
kernel: TSC cannot be used as a timesource.
kernel: Possible reasons for this are:
kernel:   You're running with Speedstep,
kernel:   You don't have DMA enabled for your hard disk (see hdparm),
kernel:   Incorrect TSC synchronization on an SMP system (see dmesg).
kernel: Falling back to a sane timesource now.


How reproducible:
easy, just add the options and reboot.

Steps to Reproduce:
1. Add 'divider=4 clock=tsc' to kernel parameters
2. reboot
3. on reboot, run dmesg | egrep -i 'clock|time|tsc|pit|lost'

Actual results:
TSC clocksource declared unstable.

Expected results:
TSC clocksource works.

Additional info:
I instrumented the 4.7 kernel -- timer_tsc.c, mark_offset_tsc():

       if (lost >= 2) {
printk("delta %ld, lost %ld, delay_at_last_interrupt %d\n", delta, lost,
delay_at_last_interrupt);

On boot the messages right before it drops the TSC as a clocksource are:

delta 4000, lost 4, delay_at_last_interrupt 1
delta 4000, lost 4, delay_at_last_interrupt 1
delta 3999, lost 3, delay_at_last_interrupt 1
delta 4002, lost 4, delay_at_last_interrupt 1

At Marcelo's suggestion I changed HZ to REAL_HZ and the TSC clocksource works fine with the divider option. If you look at mark_offset_pmtmr, it uses REAL_HZ instead of HZ, so it appears to be an oversight on the TSC clocksource.