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    SubjectPoor KVM guest performance on an HP rack server

    We have an HP Proliant DL580G5 rack server. It has 4 Intel Xeon X7460(6
    core, 2.67GHz, 16MB L3) processor with 32GB of memory. /proc/cpuinfo has
    24 x the following entry:

    processor : 23
    vendor_id : GenuineIntel
    cpu family : 6
    model : 29
    model name : Intel(R) Xeon(R) CPU X7460 @ 2.66GHz
    stepping : 1
    cpu MHz : 2666.891
    cache size : 16384 KB
    physical id : 3
    siblings : 6
    core id : 5
    cpu cores : 6
    apicid : 29
    initial apicid : 29
    fdiv_bug : no
    hlt_bug : no
    f00f_bug : no
    coma_bug : no
    fpu : yes
    fpu_exception : yes
    cpuid level : 11
    wp : yes
    flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge
    mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe lm
    constant_tsc arch_perfmon pebs bts xtopology pni dtes64 monitor ds_cpl
    vmx est tm2 ssse3 cx16 xtpr pdcm dca sse4_1 lahf_lm tpr_shadow vnmi
    bogomips : 5333.59
    clflush size : 64


    I'm running on top of it. We were actually planning to use
    it for a virtualization server for giving people dedicated *guest*
    access for their personal compile-farm needs.

    For testing purposes, we created a guest VM ( too) on top of it
    with 2GB of virtual memory stored in a raw partition:

    qemu-kvm -cpu host -smp 2 -m 2047 -drive
    file=/dev/cciss/c1d0p1,if=virtio,cache=none,boot=on -net
    nic,model=virtio,macaddr=DE:AD:BE:EF:10:28 -net
    tap,ifname=tap0,script=/usr/bin/qemu-ifup -k tr -nographic -daemonize

    The problem is that I'm seeing very poor performance within the guest.
    I've googled a bit and seen similar bug reports/discussions ending with
    some tweaks (setting rotational to 1 for virtio_blk, using cache=none,
    etc.) and an explanation from Avi Kivity about the bad scalability of
    KVM on pre-Nehalem boxes under high build load.

    But I fear that I'm far behind that *bad scalability*. I've made some
    comparisons with my QuadCore Q8300 (2MB cache) box. I won't give the
    whole numbers but for example,

    Running the autotools configure script of CUPS on that KVM guest (I can
    easily follow the output of configure line per line, it really really
    waits on some checks):

    real 0m52.876s
    user 0m4.892s
    sys 0m55.705s

    On the host (while running the guest vm):

    real 0m8.193s
    user 0m3.099s
    sys 0m4.055s

    On the quadcore box:

    real 0m8.424s
    user 0m2.651s
    sys 0m2.879s

    Both with cold cache (echo 3 > /proc/sys/vm/drop_caches)

    So it's not even a high build load. I've tried with -smp 8 (which showed
    worse numbers than -smp 2 and 4), with IDE instead of virtio, without
    -cpu host parameter but can't get near 30 (I've got 35 seconds with
    tuning read_ahead_kb, on top of IDE instead of virtio, etc.) seconds at all.

    I've also tried hugetlbfs for backing the memory within the guest.

    I'm using the latest kvm-mod-2.6.32 built on top of

    So is this huge performance difference should be accepted as normal or
    am I missing some big things?

    Thanks a lot
    Ozan Caglayan

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      Last update: 2009-12-13 02:25    [W:0.024 / U:6.248 seconds]
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