Messages in this thread | | | Date | Mon, 13 Jun 2005 11:27:23 -0700 | From | Tony Lindgren <> | Subject | Re: [PATCH] Dynamic tick for x86 version 050609-2 |
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* Srivatsa Vaddagiri <vatsa@in.ibm.com> [050613 10:09]: > Hi Tony, > I went through the dynamic-tick patch on your website > (patch-dynamic-tick-2.6.12-rc6-050610-1) and was having some > questions about it: > > 1. dyn_tick->skip is set to the number of ticks that have > to be skipped. This is set on the CPU which is the last > (in online_map) to go idle and is based on when that > CPU's next timer is set to expire. > > Other CPUs also seem to use the same interval > to skip ticks. Shouldnt other CPU check their nearest timer > rather than blindly skipping dyn_tick->skip number of ticks?
Probably, unless the wake-up of the first CPU will also wake up the rest.
> > 2. reprogram_apic_timer seems to reprogram the count-down > APIC timer (APIC_TMICT) with an integral number of apic_timer_val. > How accurate will this be? Shouldnt this take into account > that we may not be reprogramming the timer on exactly "jiffy" > boundary?
The timer reprogramming functions should be converted to use usecs. We just currently get the time in jifies from next_timer_interrupt().
> 3. Is there any strong reason why you reprogram timers only when > _all_ CPUs are idle?
I don't know this for sure. It seemed like the safest way to go for now.
> 4. In what aspects you think does your patch differ from VST (other > than not relying on HRT!)?
Dyntick uses next_timer_interrupt(), which is already part of the mainline kernel. It also works with PIT + PM timer or TSC.
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