In qemu 0.14 cache=writeback and cache=none are expected to perform well. The default cache=writethrough is a very conservative setting which is slow by design. I'm pretty sure that it has always been slow, even before 0.12.5.
I think that the specific problem with savevm may be related to the VM state being saved in too small chunks. With cache=writethrough this will hurt most.
In qemu 0.14 cache=writeback and cache=none are expected to perform well. The default cache=writethrough is a very conservative setting which is slow by design. I'm pretty sure that it has always been slow, even before 0.12.5.
I think that the specific problem with savevm may be related to the VM state being saved in too small chunks. With cache=writethrough this will hurt most.