Hi Jan, On Tue, Dec 17, 2013 at 7:21 PM, Jan Kiszka <jan.kiszka@xxxxxxxxxxx> wrote: > 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. My CPU is Intel(R) Xeon(R) CPU E5620 @ 2.40GHz. Besides, what do you mean by arbitrary frequencies? Arthur > > 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 -- Arthur Chunqi Li Department of Computer Science School of EECS Peking University Beijing, China -- 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
