> -----Original Message----- > From: kvm-owner@xxxxxxxxxxxxxxx [mailto:kvm-owner@xxxxxxxxxxxxxxx] On > Behalf Of Jan Kiszka > Sent: Thursday, May 19, 2016 11:04 PM > To: Yunhong Jiang <yunhong.jiang@xxxxxxxxxxxxxxx>; kvm@xxxxxxxxxxxxxxx > Cc: rkrcmar@xxxxxxxxxx; pbonzini@xxxxxxxxxx > Subject: Re: [RFC PATCH 0/5] Utilizing VMX preemption for timer > virtualization > > On 2016-05-20 03:44, 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. > > IIRC, VMX preemption timer was broken on several older CPUs. That was > one reason we didn't use it to emulated nested preemption timer. Were > all those CPUs also not exposing the TCP deadline timer? > > In any case, just checking for the feature bit like you do in patch 2 > shouldn't be enough to catch those CPUs. Or were there microcode patches > distributed by now that translated the errata into bit removals? I didn't know about this and will check internally. Replying on outlook now because linux side is broken. Sorry if anything wrong on the format. --jyh > > Jan > -- > 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 -- 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
