[9fans] a quick comparison of qemu and xen - Plan9

This is a discussion on [9fans] a quick comparison of qemu and xen - Plan9 ; this is qemu without kqemu, since I have had problems with that. build a kernel, for ppc (bg/l really) qemu: 4 minutes 59.86u 53.93s 233.60r mk xen 3 4.90u 5.06s 15.89r mk This is the identical tree, I tar'ed it ...

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Thread: [9fans] a quick comparison of qemu and xen

  1. [9fans] a quick comparison of qemu and xen

    this is qemu without kqemu, since I have had problems with that.

    build a kernel, for ppc (bg/l really)

    qemu: 4 minutes

    59.86u 53.93s 233.60r mk

    xen 3
    4.90u 5.06s 15.89r mk

    This is the identical tree, I tar'ed it up from the qemu instance, put
    it in the xen instance, and typed
    mk clean && mk
    in each one.

    that's a ratio of roughly 15:1. Yes, surprised me too. I will try to
    get a qemu with a working kqemu to do a more fair comparison.

    ron

  2. Re: [9fans] a quick comparison of qemu and xen

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    IIRC, without kqemu, qemu does actual per-instruction emulation, even
    if running on the same platform.
    15:1 is actually pretty impressive!

    Paul

    On 13-Feb-07, at 7:10 PM, ron minnich wrote:

    > this is qemu without kqemu, since I have had problems with that.
    >
    > build a kernel, for ppc (bg/l really)
    >
    > qemu: 4 minutes
    >
    > 59.86u 53.93s 233.60r mk
    >
    > xen 3
    > 4.90u 5.06s 15.89r mk
    >
    > This is the identical tree, I tar'ed it up from the qemu instance, put
    > it in the xen instance, and typed
    > mk clean && mk
    > in each one.
    >
    > that's a ratio of roughly 15:1. Yes, surprised me too. I will try to
    > get a qemu with a working kqemu to do a more fair comparison.
    >
    > ron


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  3. Re: [9fans] a quick comparison of qemu and xen

    On 2/13/07, Paul Lalonde wrote:
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    >
    > IIRC, without kqemu, qemu does actual per-instruction emulation, even
    > if running on the same platform.


    well, from my reading, that is not actually right. But my reading
    might be wrong :-)

    last time I had kqemu that worked right, the ratio was 4;1 in favor of xen.

    ron

  4. Re: [9fans] a quick comparison of qemu and xen

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    Without kqemu, qemu uses dynamic translation/jit compilation to
    emulate the target architecture. kqemu bypasses the jit engine and
    traps exceptions in the user code. It does not use the hardware
    virtualization features, giving Xen the advantage there.

    Paul

    On 13-Feb-07, at 8:42 PM, ron minnich wrote:

    > On 2/13/07, Paul Lalonde wrote:
    >> -----BEGIN PGP SIGNED MESSAGE-----
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    >>
    >> IIRC, without kqemu, qemu does actual per-instruction emulation, even
    >> if running on the same platform.

    >
    > well, from my reading, that is not actually right. But my reading
    > might be wrong :-)
    >
    > last time I had kqemu that worked right, the ratio was 4;1 in favor
    > of xen.
    >
    > ron


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  5. Re: [9fans] a quick comparison of qemu and xen

    On 2/14/07, Paul Lalonde wrote:
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    > Without kqemu, qemu uses dynamic translation/jit compilation to
    > emulate the target architecture.


    Right. So once you get a bit of jit compiled you're native.

    >kqemu bypasses the jit engine and
    > traps exceptions in the user code. It does not use the hardware
    > virtualization features, giving Xen the advantage there.


    my measurements were on a box without hardware virtualization.

    ron

  6. Re: [9fans] a quick comparison of qemu and xen

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    But a quick perusal of the qemu papers shows that they only use a 16
    meg code cache, and flush the whole cache when full. I'm betting
    compiling a kernel takes a few re-jittings.

    That said, 15:1 is still a huge difference.

    Paul

    On 14-Feb-07, at 6:13 AM, ron minnich wrote:

    > On 2/14/07, Paul Lalonde wrote:
    >> -----BEGIN PGP SIGNED MESSAGE-----
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    >>
    >> Without kqemu, qemu uses dynamic translation/jit compilation to
    >> emulate the target architecture.

    >
    > Right. So once you get a bit of jit compiled you're native.
    >
    >> kqemu bypasses the jit engine and
    >> traps exceptions in the user code. It does not use the hardware
    >> virtualization features, giving Xen the advantage there.

    >
    > my measurements were on a box without hardware virtualization.
    >
    > ron


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  7. Re: [9fans] a quick comparison of qemu and xen

    i wouldn't think so.

    ; size 8c 8l rc mk
    228248t + 35040d + 35960b = 299248 8c
    65004t + 17368d + 69540b = 151912 8l
    82972t + 10436d + 13528b = 106936 rc
    82781t + 8344d + 32412b = 123537 mk

    what am i forgetting that's 15.5MB of code?

    - erik

  8. Re: [9fans] a quick comparison of qemu and xen

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    The flush after each separate pass is run on each file? That would
    be my first guess.

    But this is all theoretical - I've not stopped to actually measure
    the thing.

    Paul

    On 14-Feb-07, at 6:34 AM, erik quanstrom wrote:

    > i wouldn't think so.
    >
    > ; size 8c 8l rc mk
    > 228248t + 35040d + 35960b = 299248 8c
    > 65004t + 17368d + 69540b = 151912 8l
    > 82972t + 10436d + 13528b = 106936 rc
    > 82781t + 8344d + 32412b = 123537 mk
    >
    > what am i forgetting that's 15.5MB of code?
    >
    > - erik


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