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aca6ff29c4
There is a downside of always-poll since poll is still happened for idle
vCPUs which can waste cpu usage. This patchset add the ability to adjust
halt_poll_ns dynamically, to grow halt_poll_ns when shot halt is detected,
and to shrink halt_poll_ns when long halt is detected.
There are two new kernel parameters for changing the halt_poll_ns:
halt_poll_ns_grow and halt_poll_ns_shrink.
no-poll always-poll dynamic-poll
-----------------------------------------------------------------------
Idle (nohz) vCPU %c0 0.15% 0.3% 0.2%
Idle (250HZ) vCPU %c0 1.1% 4.6%~14% 1.2%
TCP_RR latency 34us 27us 26.7us
"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 3.4%~12.8% CPUs/second and get close
to no-polling overhead levels by using the dynamic-poll. The savings
should be even higher for higher frequency ticks.
Suggested-by: David Matlack <dmatlack@google.com>
Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
[Simplify the patch. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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| .. | ||
| arm | ||
| async_pf.c | ||
| async_pf.h | ||
| coalesced_mmio.c | ||
| coalesced_mmio.h | ||
| eventfd.c | ||
| irqchip.c | ||
| Kconfig | ||
| kvm_main.c | ||
| vfio.c | ||
| vfio.h | ||