I recently installed a new Debian Wheezy server with KVM (the "KVM Host") then installed a Debian VM on the KVM (the "VM"), and got very bad performance on the VM. Looking through dmesg on the VM, I noticed lot's of messages like:
task foo:1234 blocked for more than 120 seconds
(even for tasks like scp, apt-get).
After much Googling and reading, I decided I would first experiment with changing the kernel task scheduler on the VM, but I couldn't work out how to do that. So my first question:
- how do you change the kernel task scheduler on Linux? Is it via some setting in /sys/kernel, compiling a custom kernel, or some other way?
My KVM Host filesystem is ext4 on top of md RAID1 (mirroring). Reading suggested maybe my problems are caused by ext4/mirroring. So my second question:
- any suggestions or guides on recommended ways to setup KVM?
I couldn't find anything useful on the KVM website. A Youtube search on "kvm performance" produced lots of videos, but all at the ultra-geek level, nothing basic. The KVM doco has a couple of books in German, but my German consists of "nein" and "ja" from Shultz in Hogan's Heroes :-)