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Date: Mon, 21 Jan 2008 22:31:09 +0100 From: Eric Dumazet <dada1@...mosbay.com> To: Chris Friesen <cfriesen@...tel.com> CC: netdev@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: questions on NAPI processing latency and dropped network packets 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 ? tcpdump on the host will lie, since timestamps are probably going to be host timestamps, giving the time of RX dequeing, and not time of packets arrival given by NIC. > > If I bump the rx ring size up to 4096, we can handle all the packets and > we still have 44% idle on cpu0 and 27% idle on cpu1. > > 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. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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