Aurelien Jarno wrote: > Avi Kivity a écrit : > >> Aurelien Jarno wrote: >> >>> The bad news is that kvm-14 seems to be a lot slower than kvm-12 + >>> modules from kernel 2.6.20. This is the case with a GNU/kFreeBSD guest. >>> kvm-12 was about 1.5 time faster than qemu + kqemu. kvm-20 is slower >>> than qemu without kqemu... >>> >>> Does anybody have an idea about this performance regression? >>> >>> >> What is your workload? How are you measuring performance? >> > > Sorry to answer only now, it took me some time to do some more > measurements and have some numbers. I am simply building a Debian > package (simulpic) and measuring the build time. Basically the command is: > > apt-get source simulpic > cd simulpic-2005-1-28 > time debuild -uc us > > It surely not a performance index, but I guess it is ok to compare > performances between version. It is also quite representative of my use > of the machine. >
Real workloads (likr this) are more important than synthetic benchmarks. > The guest is Debian GNU/kFreeBSD amd64 (ie FreeBSD kernel + GNU libc). > It is accessed via ssh, and kvm is started with -nographic, so there is > no influence of xorg. > > I am doing my tests on an Athlon X2 3800+ machine, running a 2.6.20 > kernel. During all my tests, the machine is not loaded with other tasks > (except systems tasks), so qemu or kvm have a full core available. Top > shows that the core is used between 95 and 100% during the whole build > in all cases. > > The tests I have made are presented below. In all cases I have verified > that the real time correspond to the time of my wall clock, it is > correct in all case given the resolution of my wall clock (1 s): > > qemu > ---- > real 3m16.626s > user 2m22.654s > sys 0m41.738s > Is this qemu 0.8.2 or qemu 0.9.0? > qemu + kqemu > ------------ > real 0m51.529s > user 0m11.775s > sys 0m36.215s > > kvm 12 + modules from kernel 2.6.20 > ----------------------------------- > real 0m30.635s > user 0m16.357s > sys 0m8.511s > > kvm 12 > ------ > real 0m25.357s > user 0m16.259s > sys 0m6.496s > > kvm 13 > ------ > real 0m23.415s > user 0m15.177s > sys 0m5.811s > So far so good. Steady improvement. The low system time indicates a lot of I/O and inefficiency in the qemu device emulation (guest time is charged as system time). > kvm 14 > ------ > real 7m47.310s > user 5m17.359s > sys 2m3.184s > > > Using kvm 14, the system is clearly not responsive at all. You can see > that without running a benchmark. > kvm-14 is mostly qemu 0.9.0. Do you get the same results with kvm-14 -no-kvm? What is your disk image file format, or are you using a partition? Do the results change (on kvm-14) if you pin the guest to a core with 'taskset 1 qemu ...' Thank you for taking the time to do real measurements and report the results clearly. That makes it possible (I hope) to find the cause and fix it. -- Do not meddle in the internals of kernels, for they are subtle and quick to panic. ------------------------------------------------------------------------- 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 [email protected] https://lists.sourceforge.net/lists/listinfo/kvm-devel
