[9fans] I/O load crashes Qemu - Plan9

This is a discussion on [9fans] I/O load crashes Qemu - Plan9 ; > Any good recommended lecture to learn about good virtualization? i think this is an interesting approach. note that some code runs faster under the vx32 than natively, though the title seems to hint that there are varying definitions of ...

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Thread: [9fans] I/O load crashes Qemu

  1. Re: [9fans] I/O load crashes Qemu

    > Any good recommended lecture to learn about good virtualization?

    i think this is an interesting approach. note that some code runs faster
    under the vx32 than natively, though the title seems to hint that there
    are varying definitions of virtualization.

    http://swtch.com/~rsc/papers/vx32-usenix2008.pdf

    > I imagine that the biggest issue is to avoid a racing condition
    > between the two(or 'n') running kernels.


    two different kernels can't race as they share no resources.
    in the hypervisor, races can be taken care of with the same techniques
    that work on any other multithreaded program.

    so, if performance is not an issue, a single threaded hypervisor could
    schedule any number of guests. then there are no locking problems at all.

    > Then... Would it be very hard to build an fs that allows to share real
    > hardware with another kernel running alongside plan 9? I imagine that
    > the so called hypervisors are kind of a "(exo-)scheduler"


    this is already possible. any number of plan 9 cpu servers may share
    a single fileserver. no virtualization needed.

    > You don't need this sort of code in a virtualizable processor.
    > See for example
    > http://en.wikipedia.org/wiki/Popek_a...n_requirements


    i'm not convinced that the illusion that the virtualized environment
    is in every way equivalent to the bare iron is always useful or worth
    the effort. why should a virtualized operating system need to worry
    about what nic the machine has?

    for example vmware doesn't provide this sort of virtualized environment.
    it provides the same virtual network card interface regardless of
    what hardware the machine has.

    - erik



  2. Re: [9fans] I/O load crashes Qemu

    On Fri, 13 Jun 2008 19:52:22 EDT erik quanstrom wrote:
    > > You don't need this sort of code in a virtualizable processor.
    > > See for example
    > > http://en.wikipedia.org/wiki/Popek_a...ion_requiremen

    > ts
    >
    > i'm not convinced that the illusion that the virtualized environment
    > is in every way equivalent to the bare iron is always useful or worth
    > the effort. why should a virtualized operating system need to worry
    > about what nic the machine has?


    Well the URL was more to get the point across. Whether your
    virtual OS uses simplified virtual devices or emulated real
    devices, you shouldn't have to emulate each instruction in
    software!

    I won't argue with "worth the effort" but it can be useful
    (e.g. running dusty decks, debugging etc).

    My argument is more that real device intefaces should be
    designed to make virtualization efficient.

    > for example vmware doesn't provide this sort of virtualized environment.
    > it provides the same virtual network card interface regardless of
    > what hardware the machine has.


    It is doable but it took them years to get there and provide
    good efficiency. May be even more years that VM/370?!


  3. Re: [9fans] I/O load crashes Qemu

    I am going to defend QEMU

    I've run a Plan 9 auth/cpu server on there for 8 months or so with no
    problems beyond those of my own construction.

    I am emulating x86-32 on a pre-VT Opteron AMD-64 (though I only found
    out about the difference *after* I bought it) and have kqemu.ko loaded,
    I run Debian. My Qemu is 0.9.1 though I used 0.9.0 for a while - I
    upgraded to take advantage of PXE booting in 0.9.1 and compiled it from
    the tar.gz

    I've not done much heavy I/O though I have made numerous pdf's with it
    with CGI on httpd. I've also produced my own installer isos with it
    which included plan9.iso & plan9.iso.bz2 in the iso.

    I've used it for fancy networking tricks with vde_switch and tap0.

    I use qcow images and I think they are sparse files.

    I have borked the file system with it, though it was my own fault.


    matt


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