2016-05-25 1:15 GMT+08:00 Christian Borntraeger <borntraeger@xxxxxxxxxx>: > On 05/24/2016 09:57 AM, Wanpeng Li wrote: >> From: Wanpeng Li <wanpeng.li@xxxxxxxxxxx> >> >> If an emulated lapic timer will fire soon(in the scope of 10us the >> base of dynamic halt-polling, lower-end of message passing workload >> latency TCP_RR's poll time < 10us) we can treat it as a short halt, >> and poll to wait it fire, the fire callback apic_timer_fn() will set >> KVM_REQ_PENDING_TIMER, and this flag will be check during busy poll. >> This can avoid context switch overhead and the latency which we wake >> up vCPU. >> >> This feature is slightly different from current advance expiration >> way. Advance expiration rely on the vCPU is running(do polling before >> vmentry). But in some cases, the timer interrupt may be blocked by >> other thread(i.e., IF bit is clear) and vCPU cannot be scheduled to >> run immediately. So even advance the timer early, vCPU may still see >> the latency. But polling is different, it ensures the vCPU to aware >> the timer expiration before schedule out. >> >> echo HRTICK > /sys/kernel/debug/sched_features in dynticks guests. >> >> Context switching - times in microseconds - smaller is better >> ------------------------------------------------------------------------- >> Host OS 2p/0K 2p/16K 2p/64K 8p/16K 8p/64K 16p/16K 16p/64K >> ctxsw ctxsw ctxsw ctxsw ctxsw ctxsw ctxsw >> --------- ------------- ------ ------ ------ ------ ------ ------- ------- >> kernel Linux 4.6.0+ 7.9800 11.0 10.8 14.6 9.4300 13.0 10.2 vanilla >> kernel Linux 4.6.0+ 15.3 13.6 10.7 12.5 9.0000 12.8 7.38000 poll >> >> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx> >> Cc: Radim Krčmář <rkrcmar@xxxxxxxxxx> >> Cc: David Matlack <dmatlack@xxxxxxxxxx> >> Cc: Christian Borntraeger <borntraeger@xxxxxxxxxx> >> Cc: Yang Zhang <yang.zhang.wz@xxxxxxxxx> >> Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxx> >> --- >> v3 -> v4: >> * add module parameter halt_poll_ns_timer >> * rename patch subject since lapic maybe just for x86. >> v2 -> v3: >> * add Yang's statement to patch description >> v1 -> v2: >> * add return statement to non-x86 archs >> * capture never expire case for x86 (hrtimer is not started) >> >> arch/arm/include/asm/kvm_host.h | 4 ++++ >> arch/arm64/include/asm/kvm_host.h | 4 ++++ >> arch/mips/include/asm/kvm_host.h | 4 ++++ >> arch/powerpc/include/asm/kvm_host.h | 4 ++++ >> arch/s390/include/asm/kvm_host.h | 4 ++++ >> arch/x86/kvm/lapic.c | 11 +++++++++++ >> arch/x86/kvm/lapic.h | 1 + >> arch/x86/kvm/x86.c | 5 +++++ >> include/linux/kvm_host.h | 1 + >> virt/kvm/kvm_main.c | 15 +++++++++++---- >> 10 files changed, 49 insertions(+), 4 deletions(-) > [...] > > @@ -1966,7 +1970,7 @@ static void grow_halt_poll_ns(struct kvm_vcpu *vcpu) >> grow = READ_ONCE(halt_poll_ns_grow); >> /* 10us base */ >> if (val == 0 && grow) >> - val = 10000; >> + val = halt_poll_ns_timer; > > Drop this hunk and leave this at 10000, so that a user can disable the timer > logic, but keep the old polling? I see, sorry for misunderstand you in v3. Regards, Wanpeng Li -- 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
