On Thu, May 19, 2016 at 06:44:58PM -0700, Yunhong Jiang wrote: > The VMX-preemption timer is a feature on VMX, it counts down, from the > value loaded by VM entry, in VMX nonroot operation. When the timer > counts down to zero, it stops counting down and a VM exit occurs. > > The VMX preemption timer for tsc deadline timer virtualization. The > VMX preemption timer is armed when the vCPU is running, and a VMExit > will happen if the virtual TSC deadline timer expires. > > When the vCPU thread is scheduled out, the tsc deadline timer > virtualization will be switched to use the current solution, i.e. use > the timer for it. It's switched back to VMX preemption timer when the > vCPU thread is scheduled int. > > This solution replace the complex OS's hrtimer system, and also the > host timer interrupt handling cost, with a preemption_timer VMexit. It > fits well for some NFV usage scenario, when the vCPU is bound to a > pCPU and the pCPU is isolated, or some similar scenarioes. > > However, it possibly has impact if the vCPU thread is scheduled in/out > very frequently, because it switches from/to the hrtimer emulation a > lot. A module parameter is provided to turn it on or off. > > Signed-off-by: Yunhong Jiang <yunhong.jiang@xxxxxxxxx> Hi Yunhong Jiang, This adds cost to the VM-exit and VM-entry paths (additional instructions and i-cache pressure). Also it adds cost to kvm_sched_out. What is the benefit the switch from external interrupt to VMX preemption timer brings? -- 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
