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. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
