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    SubjectRe: big picture UDP/IP performance question re 2.6.18 -> 2.6.32
    On 10/06/2011 11:40 PM, Eric Dumazet wrote:
    > Le jeudi 06 octobre 2011 à 23:27 -0400, a écrit :

    >> If the older kernels are switching to NAPI
    >> for much of surge and the switching out
    >> once the pulse falls off, it might
    >> conceivably result in much better latency
    >> and overall performance.

    > Thats exactly the opposite : Your old kernel is not fast enough to
    > enter/exit NAPI on every incoming frame.
    > Instead of one IRQ per incoming frame, you have less interrupts :
    > A napi run processes more than 1 frame.
    > Now increase your incoming rate, and you'll discover a new kernel will
    > be able to process more frames without losses.

    I wonder if it would make sense to adjust the interrupt mitigation
    parameters in the NIC to allow it to accumulate a few packets before
    interrupting the CPU. We had good luck using this to reduce interrupt
    rate on a quasi-pathological case where we were bouncing in and out of
    NAPI because we were *just* fast enough to keep up with incoming packets.


    Chris Friesen
    Software Developer
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