Messages in this thread | | | Subject | Re: [PATCH RFC 2/2] kvm: Be courteous to other VMs in overcommitted scenario in PLE handler | From | Peter Zijlstra <> | Date | Mon, 24 Sep 2012 17:52:09 +0200 |
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On Mon, 2012-09-24 at 17:43 +0200, Avi Kivity wrote: > Wouldn't this correspond to the scheduler interrupt firing and causing a > reschedule? I thought the timer was programmed for exactly the point in > time that CFS considers the right time for a switch. But I'm basing > this on my mental model of CFS, not CFS itself.
No, we tried this for hrtimer kernels for a while, but programming hrtimers the whole time (every actual task-switch) turns out to be far too expensive. So we're back to HZ ticks and 'polling' the preemption state.
Even if we remove all the hrtimer infrastructure overhead (can do with a few hacks) setting the hardware requires going out to the LAPIC, which is stupid slow.
Some hardware actually has fast/reliable/usable timers, sadly none of it is popular.
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