v4 -> v5: * set base case 10us and max poll time 500us * handle short/long halt, idea from David, many thanks David ;-) v3 -> v4: * bring back grow vcpu->halt_poll_ns when interrupt arrives and shrinks when idle VCPU is detected v2 -> v3: * grow/shrink vcpu->halt_poll_ns by *halt_poll_ns_grow or /halt_poll_ns_shrink * drop the macros and hard coding the numbers in the param definitions * update the comments "5-7 us" * remove halt_poll_ns_max and use halt_poll_ns as the max halt_poll_ns time, vcpu->halt_poll_ns start at zero * drop the wrappers * move the grow/shrink logic before "out:" w/ "if (waited)" v1 -> v2: * change kvm_vcpu_block to read halt_poll_ns from the vcpu instead of the module parameter * use the shrink/grow matrix which is suggested by David * set halt_poll_ns_max to 2ms 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. Wanpeng Li (3): KVM: make halt_poll_ns per-VCPU KVM: dynamic halt_poll_ns adjustment KVM: trace kvm_halt_poll_ns grow/shrink include/linux/kvm_host.h | 1 + include/trace/events/kvm.h | 30 ++++++++++++++++++++ virt/kvm/kvm_main.c | 69 ++++++++++++++++++++++++++++++++++++++++++---- 3 files changed, 95 insertions(+), 5 deletions(-) -- 1.9.1 -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
