[libvirt-users] Questions about CMT event statistic

Hi I'm testing cmt event of libvirt, and I have two questions. I will be very grateful if someone can give me some help. Q1:"virsh domstats --perf" and linux perf tool has different result. I have a guest with cmt event enabled, start guest and get perf statistic every 1s: # while true; do virsh domstats rhel7.2-1030 --perf; sleep 1; done In the meanwhile, I use perf tool to get the llc_occupancy of qemu-kvm process: # pidof qemu-kvm 16779 # perf stat -a -e intel_cqm/llc_occupancy/ -I 1000 -p 16779 sleep 100 And I compare the output of the above two commands, and find that they're so different: The output of "virsh domstats" The output of "perf" tool perf.cache=15753216 49152 Bytes perf.cache=14499840 11526144 Bytes perf.cache=14499840 11599872 Bytes perf.cache=14499840 11599872 Bytes perf.cache=14499840 11599872 Bytes perf.cache=14499840 11599872 Bytes perf.cache=14499840 11599872 Bytes perf.cache=14499840 11599872 Bytes perf.cache=8380416 11649024 Bytes perf.cache=8380416 11649024 Bytes perf.cache=8380416 11821056 Bytes perf.cache=8380416 11845632 Bytes perf.cache=8380416 11845632 Bytes perf.cache=8380416 11845632 Bytes perf.cache=8380416 11845632 Bytes perf.cache=8380416 11845632 Bytes perf.cache=8380416 11845632 Bytes perf.cache=8380416 11845632 Bytes perf.cache=8380416 11845632 Bytes perf.cache=8380416 11845632 Bytes perf.cache=8380416 11870208 Bytes perf.cache=8380416 11870208 Bytes perf.cache=8380416 11845632 Bytes ... ... I don't know if it's appropriate to do this comparison, but I'm still curious why they get different results. Q2:Disable&enable cmt at runtime, then "virsh domstats" will output perf.cache=0 # virsh perf rhel7.2-1030 --disable cmt # virsh perf rhel7.2-1030 --enable cmt # virsh domstats rhel7.2-1030 --perf Domain: 'rhel7.2-1030' perf.cache=0 Watch the output for more than two minutes, it's 0 all the time: # watch virsh domstats rhel7.2-1030 --perf Every 2.0s: virsh domstats rhel7.2-1030 --perf Wed Apr 27 17:36:01 2016 Domain: 'rhel7.2-1030' perf.cache=0 BR, Fangge Jin