Date: Wed, 14 Sep 2011 21:35:26 -0400 From: Jon Schipp <jonschipp@gmail.com> To: freebsd-performance@freebsd.org Subject: Zero-Copy for packet capture and mbuf question Message-ID: <CAB15j_CV4PKKq6_MnYsiDWhnjgffBg1KTQGw%2B3DjSb1vw0fvbg@mail.gmail.com>
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Has anyone used the zero-copy mechanism for an increased performance in packet capturing? I'm on FreeBSD 8.2-RELEASE, I was thinking about trying it. It's for a network monitoring system, it just grabs and dumps all data from all my network segments. I've noticed improvements by increasing the bpf buf size and maxbufsize which in turned increased the initial buffer size for libpcap. I'm dropping less now. In 8.2, is turning on zero-copy as simple as changing the value of net.bpf.zerocopy_enable? http://node5.blogspot.com/2009/11/very-quick-look-at-zero-copy-bpf-in.html I can't seem to find much information that shows that it's this simple. Right now it seems that if I want to use zero-copy for sends I would have to recompile the kernel with: options ZERO_COPY_SOCKETS But for receives, which is only what I'm concerned about, it seems that I just turn it on via sysctl. *I see that in 9.0 it will be on by default* Another question: I'm assuming all packets get copied to an mbuf from the NIC and then copied again to the bpf device/bpf buffer. Can anyone verify this? I don't think raising my mbufs will help, since a few hundred are free during peak hours. Will increasing the amount of mbuf clusters (nmbclusters) only help when you are pushing the threshold i.e. running out? Also, out of curiousity, is it possible to increase the amount of mbufs as opposed to the amount of mbuf clusters? Any help is appreciated. Thanks -- - Jon -- ------------------------------------------------------------------ VMB: 812-682-0231 Dubois County Linux User Group - http://www.dclinux.org Southern Indiana Computer Klub - http://sickbits.networklabs.org Bloomington FOOLS - http://www.bloomingtonfools.org/ BloomingLabs - http://www.bloominglabs.org ISSA-Kentuckiana - http://issa-kentuckiana.org GPG Key ID: 810903CB Key fingerprint = 0069 ED69 EABB DF84 5983 AD3C 6C20 BEFD 8109 03CB
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