On Mon, May 28, 2018 at 02:05:05PM +0200, Kashyap Chamarthy wrote: > Cc the QEMU Block Layer mailing list (qemu-block@xxxxxxxxxx), [Sigh; now add the QEMU BLock Layer e-mail list to Cc, without typos.] > who might > have more insights here; and wrap long lines. > > On Mon, May 28, 2018 at 06:07:51PM +0800, Chunguang Li wrote: > > Hi, everyone. > > > > Recently I am doing some tests on the VM storage+memory migration with > > KVM/QEMU/libvirt. I use the following migrate command through virsh: > > "virsh migrate --live --copy-storage-all --verbose vm1 > > qemu+ssh://192.168.1.91/system tcp://192.168.1.91". I have checked the > > libvirt debug output, and make sure that the drive-mirror + NBD > > migration method is used. > > > > Inside the VM, I use an I/O benchmark (Iometer) to generate an oltp > > workload. I record the I/O performance (IOPS) before/during/after > > migration. When the migration begins, the IOPS dropped by 30%-40%. > > This is reasonable, because the migration I/O competes with the > > workload I/O. However, during almost the last period of migration > > (which is 66s in my case), the IOPS dropped dramatically, from about > > 170 to less than 10. I also show the figure of this experiment in the > > attachment of this email. > > [The attachment should arrive on the 'libvirt-users' list archives; but > it's not there yet -- > https://www.redhat.com/archives/libvirt-users/2018-May/thread.html] > > > I want to figure out what results in this period with very low IOPS. > > First, I added some printf()s in the QEMU code, and knew that, this > > period occurs just before the memory migration phase. (BTW, the memory > > migration is very fast, which is just about 5s.) So I think this > > period should be the last phase of the "drive-mirror" process of QEMU. > > So then I tried to read the code of "drive-mirror" in QEMU, but failed > > to understand it very well. > > > > Does anybody know what may lead to this period with very low IOPS? > > Thank you very much. > > > > Some details of this experiment: The VM disk image file is 30GB > > (format = raw,cache=none,aio=native), and Iometer operates on an 10GB > > file inside the VM. The oltp workload consists of 33% writes and 67% > > reads (8KB request size, all random). The VM memory size is 4GB, most > > of which should be zero pages, so the memory migration is very fast. > > > > -- > > Chunguang Li, Ph.D. Candidate > > Wuhan National Laboratory for Optoelectronics (WNLO) > > Huazhong University of Science & Technology (HUST) > > Wuhan, Hubei Prov., China > > > -- > /kashyap -- /kashyap _______________________________________________ libvirt-users mailing list libvirt-users@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvirt-users
