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Re: [Xen-devel] Questions about GPLPV stability tests



The patch actually only disables HPET broadcast which has some downsides
because it effectively disables C3 states. Without C3 states Nehalem and
later CPUs cannot enter turbo-mode. So there is some loss of performance.
Would disabling any low CPU power states and turbo clocks in the BIOS,
help as well? Just curious. I have seen other 'weird' performance

I would leave the BIOS to its default and I'd guess that playing with BIOS settings only makes it worse.

issues between machines using the same hardware. Some CPU intensive
algorithm could be twice as slow running on Dom0 compared to the same
kernel without Xen. On other identical systems I didn't see that
issue. I didn't have time to investigate, but I felt there may have
been BIOS setting differences.

Xen does not use the performance governor by default which has a notable performance impact in my tests. My Xen boot config is:

kernel /xen.gz dom0_mem=1024m dom0_max_vcpus=2 cpufreq=xen:performance
module /linux-2.6.32.36-pvops0-ak2 root=/dev/sda5

Regards Andreas

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