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DragonFly kernel List (threaded) for 2006-09
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Re: Cache coherency, clustering, and Kernel virtualization

From: Matthew Dillon <dillon@xxxxxxxxxxxxxxxxxxxx>
Date: Sat, 2 Sep 2006 21:12:15 -0700 (PDT)

:So how does Userland VFS and ZFS go into this?

    Userland VFS needs to use SYSLINK.  Making progress with SYSLINK
    requires a fairly quick development cycle, one that I am not achieving
    with the current kernel build/install/reboot cycle.  It just takes too
    long, even with VMWare.

    So far I've been able to commit the basic syslink pipeing technology
    and the basic CCMS range lock, and I do consider those to be achievements,
    but both took considerably longer then they should have and it was 
    mostly due to the development cycle.   The next stage for both subsystems
    is going to be a lot more complex.

    It's going to get even worse with the clustering work.  There we aren't
    talking about a single machine any more, we are talking about multiple
    machines tied together in a cluster over a network.   I don't want
    to imagine what the development cycle is for that using real systems
    or VMWare.

    With kernel virtualization the development cycle is about 10 seconds.
    I'll be able to create a 'cluster' with a simple script that runs a
    couple of virtual kernels, and destroy it simply by hitting ^C, and
    I'll be able to test userland VFS as it will actually be coded in
    the kernel and in userland.  And if I crash a 'kernel' I won't have to
    deal with it writing to swap, or remote gdb, or any of that junk.

					Matthew Dillon 

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