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
