incorrect usleep/select delays with HZ > 2500

Daniel O'Connor doconnor at
Thu Sep 10 13:32:34 UTC 2009

On Thu, 10 Sep 2009, John Baldwin wrote:
> > $ARCH/isa/clock.c::DELAY(). I suppose with a few measurements
> > at different HZ values and some back of the envelope calculations
> > one could even determine estimate the frequency and duration
> > of those SMI interrupts!
> On recent motherboards I have seen the SMI# interrupt fire every 250
> ms with execution times ranging from 50 us to 1ms for the legacy USB
> interrupt handler.  We consistently see the TSC frequency
> miscalculated on the motherboards with the 1ms duration interrupt.  I
> suspect that the clock that drives the periodic SMI# interrupt is
> tied to the i8254 meaning that it often fires at the same time that
> the i8254 wraps causing the TSC frequency to often be wrong.

Can the calculation code disable the SMI# interrupt? Disabling legacy 
USB could be a problem if you want to use a USB keyboard with the 
loader (I think).

Daniel O'Connor software and network engineer
for Genesis Software -
"The nice thing about standards is that there
are so many of them to choose from."
  -- Andrew Tanenbaum
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