[Xen-users] benchmarks + disappointing cstate results

[Andreas Kinzler <ml@xxxxxx>]

Hello,

I do a lot of benchmarking on Xen/KVM and recently started a new set of 
benchmark runs with
special attention to cstates. Since modern Intel CPUs need C3 state for their 
turbo mode I played
with Xen option max_cstate=1 to check the effect. Normally you would expect a 
drop of performance
with max_cstate=1 since it blocks the necessary precondition of Intel Nehalem 
to enable turbo mode.
My tests show the opposite instead! Using max_cstate=1 has no effect or causes 
increases in
performance instead. The conclusion: Xen cannot use turbo mode and even worse: 
without max_cstate=1
you are penalized even more.

Regards Andreas

date: 22.07.2010
Supermicro X8SIL-F, BIOS 1.1, Intel Xeon X3450, 8 GB RAM reg ECC
benchmark: time emerge apache (apache 2.2.15 using Gentoo on x86_64)
xen with parameters "dom0_mem=1024m dom0_max_vcpus=2"
pvops0 kernel from 14.07.10 (Jeremy's xen/stable-2.6.32.x)
xenified kernel 2.6.31-xen0-r14 (from Andrew Lyon)
xenified kernel 2.6.32-xen0-r3 (from Suse backported minimal)

native linux 2.6.31.12 with maxcpus=2
        real    0m41.193s
        user    0m41.479s
        sys     0m9.609s

2.6.32-xen0-r3 + xen 3.4.3, max_cstate=1
2.6.32-xen0-r3 + xen 3.4.2
2.6.32-xen0-r3 + xen-4.0.1_rc4, max_cstate=1
        real    0m53.122s
        user    0m41.795s
        sys     0m16.233s

2.6.31-xen0-r14 + xen 3.4.2
2.6.31-xen0-r14 + xen 3.4.2, max_cstate=1
        real    0m54.670s
        user    0m41.695s
        sys     0m18.757s

2.6.31-xen0-r14 + xen 3.4.3, max_cstate=1
        real    0m56.983s
        user    0m40.767s
        sys     0m20.597s

2.6.32.16-pvops0 + xen-4.0.1_rc4, max_cstate=1
2.6.32.16-pvops0 + xen-4.0.1_rc4
2.6.32.16-pvops0 + xen 3.4.3
        real    0m58.298s
        user    0m45.319s
        sys     0m30.126s

2.6.32-xen0-r3 + xen-4.0.1-rc4
        real    0m59.352s
        user    0m39.258s
        sys     0m20.405s

2.6.32-xen0-r3 + xen 3.4.3
        real    1m1.352s
        user    0m39.682s
        sys     0m21.645s

2.6.31-xen0-r14 + xen-4.0.1-rc4
2.6.31-xen0-r14 + xen 3.4.3
        real    1m9.633s
        user    0m41.735s
        sys     0m26.326s


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