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    SubjectRe: [Xen-devel] [RFC 0/2] To introduce xenwatch multithreading (xen mtwatch)
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    Hi Wei,

    On 04/23/2018 10:09 PM, Wei Liu wrote:
    > On Sat, Apr 07, 2018 at 07:25:53PM +0800, Dongli Zhang wrote:
    >> About per-domU xenwatch thread create/destroy, a new type of xenstore node is
    >> introduced: '/local/domain/0/mtwatch/<domid>'.
    >>
    >> Suppose the new domid id 7. During the domU (domid=7) creation, the xen
    >> toolstack writes '/local/domain/0/mtwatch/7' to xenstore before the insertion
    >> of '/local/domain/7'. When the domid=7 is destroyed, the last xenstore
    >> operation by xen toolstack is to remove '/local/domain/0/mtwatch/7'.
    >>
    >> The dom0 kernel subscribes a watch at node '/local/domain/0/mtwatch'. Kernel
    >> thread [xen-mtwatch-7] is created when '/local/domain/0/mtwatch/7' is inserted,
    >> while this kernel thread is destroyed when the corresponding xenstore node is
    >> removed.
    >
    > Instead of inventing yet another node, can you not watch /local/domain
    > directly?

    Would you like to watch at /local/domain directly? Or is your question "is there
    any other way to not watch at /local/domain, while no extra xenstore node will
    be introduced"?

    Actually, the first prototype of this idea was to watch at /local/domain
    directly to get aware of the domU create/destroy, so that xen toolstack will not
    get involved. Joao Martins (CCed) had a concern on the performance as watching
    at /local/domain would lead to large amount of xenwatch events.

    Dongli Zhang

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