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 -- xen mailing list xen@xxxxxxxxxxxxxxxxxxxxxxx https://admin.fedoraproject.org/mailman/listinfo/xen
