Date: Wed, 6 Aug 2008 16:36:28 +0300 From: "Yony Yossef" <yonyossef.lists@gmail.com> To: freebsd-questions@freebsd.org Subject: Long mbuf chains Message-ID: <20def4870808060636h2d8e9082td1e486a41f9506aa@mail.gmail.com>
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Hi All I'm working on an Ethernet driver for FreeBSD 7.0. Taking network performance numbers I encountered very long mbuf chains on the sender side. The symptom is constant, always during iperf/netperf TCP stream tests with message sizes of 128 bytes (>200 mbufs per chain), 1024 bytes (30-60 mbufs per chain) and 2048 bytes. My problem is that long chains require some kind of defragmentation/cutting before it can be properly DMAd. This is pretty a expansive operation. 1. Is there a way of tuning the OS for sending limited length mbuf chains? I thought setting "net.inet.ip.maxfragsperpacket" would do it but it doesn't. 2. Is there a better way of handling this issue? Thanks, Yony
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