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Date: Mon, 21 Jan 2008 17:25:19 -0600 From: "Chris Friesen" <cfriesen@...tel.com> To: Eric Dumazet <dada1@...mosbay.com> CC: netdev@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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