Messages in this thread | | | Date | Thu, 18 Feb 2010 20:55:30 +1100 | From | Anton Blanchard <> | Subject | Re: NO_HZ migration of TCP ack timers |
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Hi Andi,
> If the nohz balancer CPU is otherwise idle, shouldn't it have enough > cycles to handle acks for everyone? Is the problem the cache line > transfer time?
Yeah, I think the timer spinlock on the nohz balancer cpu ends up being a global lock for every other cpu trying to migrate their ack timers to it.
> Sounds like something that should be controlled by the cpufreq governour's > idle predictor? Only migrate if predicted idle time is long enough. > It's essentially the same problem as deciding how deeply idle to put > a CPU. Heavy measures only pay off if the expected time is long enough.
Interesting idea, it seems like we do need a better understanding of how idle a cpu is, not just that it is idle when mod_timer is called.
Anton
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