On 2013-12-17 10:32, Arthur Chunqi Li wrote: > Hi Jan and Paolo, > > I've tried to use preemption timer in KVM to trap vcpu regularly, but > there's something unexpected. I run a VM with 4 vcpus and give them > the same preemption timer value (e.g. 1000000) with all bits set > (activate/save bits), then reset the value in preemption time-out > handler. > > Thus I expected these vcpus trap regularly in some special turns. But > I found that when the VM is not busy, some vcpus are trapped much less > frequently than others. In Intel SDM, I noticed that preemption timer > is only related to TSC, and I think all the vcpus should trap in a > similar frequency. > > Could u help me explain this phenomenon? Are you on a CPU that has non-broken preemption timer support? Anything prior Haswell is known to tick with arbitrary frequencies. BTW, we will have to re-implement preemption timer support with the help of a regular host timer due to the breakage when halting L2 (see my test case). Jan -- Siemens AG, Corporate Technology, CT RTC ITP SES-DE Corporate Competence Center Embedded Linux -- 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
