On 23/06/2017 13:59, Wanpeng Li wrote: > From: Wanpeng Li <wanpeng.li@xxxxxxxxxxx> > > Linux as a guest will prevent to program the next event to the clock event > device when the event is in the past. However, it is not guaranteed by all > the guests, the guest like kvm-unit-tests/apic.flat will write current tsc > value visible in guest to MSR_IA32_TSCDEADLINE, lapic timer which is emulated > by vmx preemption timer will program the absolute target tsc value to vmcs > preemption timer field w/ delta == 0, then plays a vmentry and an upcoming > vmx preemption timer fire vmexit dance, the lapic timer injection is delayed > for this duration. Actually the lapic timer which is emulated by hrtimer can > handle this correctly. > > This patch fixes it by firing the lapic timer and injecting a timer interrupt > immediately during the next vmentry if guest programs an expired timer to > the emulated timer device. This saves ~300 cycles on the tsc_deadline_timer > test of apic.flat. If it doesn't matter for actual guests, I'd rather not complicate the logic. Paolo
