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    SubjectRe: queue_work from interrupt Real time preemption2.6.11-rc2-RT-V0.7.37-03

    On Thu, 17 Feb 2005, Ingo Molnar wrote:
    > as long as it stays on a single CPU, could we allow softirq contexts to
    > preempt each other? I.e. we'd keep the per-CPU assumption (that is fair
    > and needed for performance anyway), but we'd allow NET_TX to preempt
    > NET_RX and vice versa. Would this corrupt the rx/tx queues? (i suspect
    > it would.)
    >
    > (anyway, by adding an explicit no-preempt section around the 'take
    > current rx queue private, then process it' on PREEMPT_RT it could be
    > made safe. I'm wondering whether there are any other deeper assumptions
    > about atomic separation of softirq contexts.)
    >

    Ingo,

    Wouldn't this cause a longer latency in these sections. I understand
    that turning preemption off doesn't stop interrupts that are not
    threaded, but especially on a UP, this would cause higher latencies for
    high priority processes when a lower priority process is heavy on network
    traffic.

    As I mentioned earlier, what would it take to be able to group
    softirq threads that should not preempt each other, but still keep
    preemption available for other threads?

    Actually, I guess I need to ask, what do you intend on doing to prioritize
    the softirq? Are you going to make a separate thread for each tasklet?
    Once I see what you're doing, I'll make something up to help handle this
    problem.

    -- Steve

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