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    SubjectRe: questions on NAPI processing latency and dropped network packets
    Eric Dumazet wrote:
    > Chris Friesen a écrit :
    >
    >> I've done some further digging, and it appears that one of the
    >> problems we may be facing is very high instantaneous traffic rates.
    >>
    >> Instrumentation showed up to 222K packets/sec for short periods (at
    >> least 1.1 ms, possibly longer), although the long-term average is down
    >> around 14-16K packets/sec.
    >
    >
    > Instrumentation done where exactly ?

    I added some code to e1000_clean_rx_irq() to track rx_fifo drops, total
    packets received, and an accurate timestamp.

    If rx_fifo errors changed, it would dump the information.

    >> Is there anything else we can do to minimize the latency of network
    >> packet processing and avoid having to crank the rx ring size up so high?

    > You have some tasks that disable softirqs too long. Sometimes, bumping
    > RX ring size is OK (but you will still have delays), sometimes it is not
    > an option, since 4096 is the limit on current hardware.

    I added some instrumentation to take timestamps in __do_softirq() as
    well. Based on these timestamps, I can see the following code sequence:

    2374604616 usec, start processing softirqs in __do_softirq()
    2374610337 usec, log values in e1000_clean_rx_irq()
    2374611411 usec, log values in e1000_clean_rx_irq()

    In between the successive calls to e1000_clean_rx_irq() the rx_fifo
    counts went up.

    Does anyone have any patchsets to track down what softirqs are taking a
    long time, and/or who's disabling softirqs?

    Chris
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