On Tue, Jul 03, 2012 at 08:59:34AM -0400, Konrad Rzeszutek Wilk wrote:
On Tue, Jul 03, 2012 at 07:16:04AM -0500, W. Michael Petullo wrote:
We have seen a significant reduction in performance in our research DomU OS kernel when running on Fedora 16 with Linux 3.4.2 vs. 3.3.7. We run
a series of benchmarks which are DomU-kernel-space-CPU-heavy; many of
these run 10x slower when using the 3.4.2 Linux kernel as Dom0.
This is a little surprising---we've been tracking the Fedora kernels for a long time with no problem like this. Did anyone else notice any changes?
Just to verify.. both the 3.3.7 and 3.4.2 Linux kernel are 'release' builds? and not debug-versions from rawhide?
Yes, they are the Fedora 16 release builds.
The commits that went in (3.4) were:
...
So one thing that you might be hitting is that now the CPU freq driver is uploading the data to the hypervisor - the hypervisor might be doing power-save stuff instead of concentrating on giving your raw performance.
So can you start with 'cpufreq=verbose,performance' on your hypervisor line.
Michael openned a bug and on it we found that the xen-acpi-processor.off=1 would solve the performance problem. What that does is to not upload C-states and P-states information to the hypervisor. So I pulled up an AMD box and found that the problem is only if hypervisor enters C-2 states. If I do 'xenpm set-max-cstate 1' it gets back to working nicely.
Wei, any ideas? This is with Xen 4.1