The HPET issue on Linux

[Sheng Yang <sheng@linux.intel.com>]

Hi Beth

I still found the emulated HPET would result in some boot failure. For 
example, on my 2.6.30, with HPET enabled, the kernel would fail check_timer(), 
especially in timer_irq_works().

The testing of timer_irq_works() is let 10 ticks pass(using mdelay()), and 
want to confirm the clock source with at least 5 ticks advanced in jiffies. 
I've checked that, on my machine, it would mostly get only 4 ticks when HPET 
enabled, then fail the test. On the other hand, if I using PIT, it would get 
more than 10 ticks(maybe understandable if some complementary ticks there). Of 
course, extend the ticks count/mdelay() time can work.

I think it's a major issue of HPET. And it maybe just due to a too long 
userspace path for interrupt injection... If it's true, I think it's not easy 
to deal with it.

-- 
regards
Yang, Sheng