On Fri, 2023-09-22 at 10:20 +0100, David Woodhouse wrote: > From: David Woodhouse <dwmw@xxxxxxxxxxxx> > > Most of the time there's no need to kick the vCPU and deliver the timer > event through kvm_xen_inject_timer_irqs(). Use kvm_xen_set_evtchn_fast() > directly from the timer callback, and only fall back to the slow path > when it's necessary to do so. > > This gives a significant improvement in timer latency testing (using > nanosleep() for various periods and then measuring the actual time > elapsed). > > Signed-off-by: David Woodhouse <dwmw@xxxxxxxxxxxx> Hm, scratch that. It brings back the race condition Paolo talks about in https://lore.kernel.org/kvm/0709ac62f664c0f3123fcdeabed3b79038cef3b6.camel@xxxxxxxxxxxxx/T/ Well, not *quite*... there's no race with clearing timer_expires because I forgot to clear it at all :) I think I'll be able to fix it up with an hrtimer_cancel() in the rare ioctl attr_get path to avoid the race.
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