Kashyap Chamarthy
2018-05-28 12:05:05 UTC
Cc the QEMU Block Layer mailing list (qemu-***@nongnu.org), who might
have more insights here; and wrap long lines.
it's not there yet --
https://www.redhat.com/archives/libvirt-users/2018-May/thread.html]
have more insights here; and wrap long lines.
Hi, everyone.
Recently I am doing some tests on the VM storage+memory migration with
"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; butRecently I am doing some tests on the VM storage+memory migration with
"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.
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
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