Dong, Eddie wrote: > Avi Kivity wrote: > >> Dong, Eddie wrote: >> >>> Avi Kivity wrote: >>> >>> >>>>> With PIC in Xen, CPU2K gets 6.5% performance gain in old 1000HZ >>>>> linux kernel, KB gets 14% gain. We also did a shared PIC model >>>>> which share PIC state among Qemu & VMM with less LOC in VMM, it >>>>> can get >>>>> similar performance gain (5.8% in my test). >>>>> BTW, at that time, PIT is in VMM already. >>>>> >>>>> >>>>> >>>> I expect that the gain in kvm will be smaller. Xen has to schedule >>>> dom0 to process the event channel (possibly on another cpu), dom0 >>>> has to schedule qemu-dm (again, possibly on another cpu), qemu does >>>> its thing, and then Xen has to schedule domU again. With kvm, we >>>> are always on the same cpu, and the only overhead is the system >>>> call, which is a few hundred nanoseconds. I expect with current >>>> hardware that it will be negligible (as a vmexit is measured in >>>> microseconds), but to become measurable as hardware improves. >>>> >>>> >>> Yes very possible. >>> We can take a quick mesurement to see how many cycles are spent in a >>> dummy I/O emulation in KVM/Qemu. In Xen, one of my old P4 3.8GHZ >>> platform takes about 50-60K cycles. We can see how many is it in KVM. >>> BTW, today Linux kernel is no longer 1000HZ :-) >>> thx,eddie >>> >>> >> There's some (old) data here: >> >> http://virt.kernelnewbies.org/KVM/Performance >> >> showing pio latency of ~5600 cycles. Note that this is on AMD, which >> takes less cycles to switch than the P4, but on the other hand, we >> still do a save/restore of the fpu state on every exit, so we can >> speed it up even more. >> > > That is great I/O performance difference between Xen & KVM though the > sample data > is too small (100 delta's were used). We can try with more samples to > let it last for several > minutes to include many scheduler events that we used before. > On the otherhand, it proves that context switch between KVM and Qemu is > quit lightweight > given that there is no domain switch and even no guest task switch in > most case. >
You may want to take a look at virtbench. It has quite a good number of microbenchmarks specifically designed for virtualized environments. http://ozlabs.org/~rusty/virtbench I use "local" for measuring KVM/Xen. Regards, Anthony Liguori > Thanks, eddie > > ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys-and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV _______________________________________________ kvm-devel mailing list kvm-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kvm-devel
