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    SubjectRe: Kernel rwlock design, Multicore and IGMP
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    Le mercredi 17 novembre 2010 à 09:30 +0800, Cypher Wu a écrit :
    > O
    > struct in_device::mr_ifc_timer. Every time when a process join/leave a
    > MC group, igmp_ifc_event() -> igmp_ifc_start_timer() will start the
    > timer on the core that the system call issued, and
    > igmp_ifc_timer_expire() will be called on that core in the bottem halt
    > of timer interrupt.
    > If we call join/leave on mutlicores that timers will run on all these
    > cores, but it seems only one or two will generate IGMP message, others
    > will only lock the list and loop throught it with nothing generated.
    >
    >

    Problem would not be timer being restarted on different cores (very
    small impact), but scanning a list in igmpv3_send_cr() with many items
    in it and expensive things, under timer handler (softirq), so adding
    spikes of latency.

    IGMP_Unsolicited_Report_Interval is 10 seconds, so we start timer in a 5
    second average.

    I am not sure there is a need to join/leave thousand of groups per
    second anyway...



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