2016-10-26 21:32 GMT+08:00 Radim Krčmář <rkrc...@redhat.com>: > 2016-10-26 14:02+0800, Wanpeng Li: >> 2016-10-25 19:43 GMT+08:00 Radim Krčmář <rkrc...@redhat.com>: >>> 2016-10-25 07:39+0800, Wanpeng Li: >>>> 2016-10-24 23:27 GMT+08:00 Radim Krčmář <rkrc...@redhat.com>: >>>>> 2016-10-24 17:09+0200, Paolo Bonzini: >>>>>> On 24/10/2016 17:03, Radim Krčmář wrote: >>>>> [...] >>>>>> >>>>>> Reviewed-by: Paolo Bonzini <pbonz...@redhat.com> >>>>>> >>>>>> Go ahead, squash it into 5/5 and commit to kvm/queue. :) >>>>> >>>>> Did that, thanks. >>>>> >>>>> Wanpeng, the code is now under your name so please check it and/or >>>>> complain. >>>> >>>> This patch 6/5 incurred regressions. >>>> >>>> - The latency of the periodic mode which is emulated by VMX preemption >>>> is almost the same as periodic mode which is emulated by hrtimer. >>> >>> Hm, what numbers are you getting? >> >> The two fixes look good to me. However, the codes which you remove in >> kvm_lapic_switch_to_hv_timer() results in different numbers. > > Which of those two results is closer to the expected duration of the > period?
The result of w/ remove is more closer to the expected duration. > >> w/o remove hlt average latency = 2398462 >> w/ remove hlt average latency = 2403845 > > Some increase is expected when removing the code, because > kvm_lapic_switch_to_hv_timer() decreased the period by mistake: > it called > > now = get_time() > > first and then did > > remaining = target - get_time() // = hrtimer_get_remaining() > > but some time has passed in between calls of get_time(), let's call the > time that passed in between as "delta", so when the function later set > the new target, > > new_target = now + remaining // = now + target - (now + delta) > > the new_target was "delta" earlier. Agreed. > > 5k cycles is a huge difference, though ... Yeah, delta can't be as large as 5k cycles. > You tested the original kvm_lapic_switch_to_hv_timer(), with fixed > advance_periodic_target_expiration()? Yes. > >>> When I ran the test with the original series, then it actually had worse >> >> Did you test this by running my kvm-unit-tests/apic_timer_latency.flat? > > Yes, I used numbers from Intel(R) Xeon(R) CPU E5-2620 v3 @ 2.40GHz, > which had TSC calibrated to 2397.223 MHz, so the expected "average > latency" with with the default 0x100000 ns period was > > 0x100000 * 2.397223 - 0x100000 = 1465094.5044479999 I agree with your remove the logic in kvm_lapic_switch_to_hv_timer() since it is more closer to the expected "average latency" now. Regards, Wanpeng Li
