This patchset adds a dynamic on/off switch for polling. This patchset
gets good performance on its own for both idle and Message Passing
workloads.
no-poll always-poll adaptive-toggle
---------------------------------------------------------------------
Idle (nohz) VCPU %c0 0.12 0.32 0.15
Idle (250HZ) VCPU %c0 1.22 6.35 1.27
TCP_RR latency 39 us 25 us 25 us
(3.16 Linux guest, halt_poll_ns=200000)
"Idle (X) VCPU %c0" is the percent of time the physical cpu spent in
c0 over 60 seconds (each VCPU is pinned to a PCPU). (nohz) means the
guest was tickless. (250HZ) means the guest was ticking at 250HZ.
The big win is with ticking operating systems. Running the linux guest
with nohz=off (and HZ=250), we save 5% CPUs/second and get close to
no-polling overhead levels by using the adaptive toggle. The savings
should be even higher for higher frequency ticks.
Since we get low idle overhead with polling now, halt_poll_ns defaults
to 200000, instead of 0. We can increase halt_poll_ns a bit more once
we have dynamic halt-polling length adjustments (Wanpeng's patch). We
should however keep halt_poll_ns below 1 ms since that is the tick
frequency used by windows.
David Matlack (1):
kvm: adaptive halt-polling toggle
Wanpeng Li (1):
KVM: make halt_poll_ns per-VCPU
include/linux/kvm_host.h | 1 +
include/trace/events/kvm.h | 23 ++++++----
virt/kvm/kvm_main.c | 111 ++++++++++++++++++++++++++++++++++-----------
3 files changed, 99 insertions(+), 36 deletions(-)
--
2.5.0.457.gab17608
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