On Wed, 5 Dec 2007, Vlad GALU wrote:
I've had several reports of significantly improved packet capture rates at
high speeds with it, but it's not yet in the tree because we feel it needs
more evaluation and review. I hope to ship some form of zero-copy BPF
buffer support in FreeBSD 8, and possibly even MFC it. Any feedback you
might have would be most helpful.
Having sent you the patch, I should have let you know that you'll need to:
- Add options BPF_ZEROCOPY to your kernel configuration to enable the
zero-copy buffering mode.
- Make sure the kernel and libpcap are rebuild following the application of
the patch and dropping in the tarball.
- setenv BPF_ZERO_COPY before running tcpdump or other BPF-based tools to
enable the zero-copy buffer mode.
The patch includes both kernel changes (abstract the buffer model, add a
new buffer model) and user space changes (updated libpcap to speak the new
model, selected right now with the environmental variable). Presumably if
merged, zero-copy BPF buffers would be used by default via libpcap if
present in the kernel, but right now this is all for evaluation purposes.
Thanks, Robert! I'll start running a few tests next week, I'm waiting for
some hardware to arrive first.
I've put up an updated tarball based on some recent changes here:
http://www.watson.org/~robert/freebsd/20071226-zcopybpf.tgz
The main changes since this last drop are:
- BPF_ZERO_COPY environmental variable renamed to BPF_ZEROCOPY to match kernel
option name.
- libpcap support for zero-copy BPF buffers reworked to avoid unconditional
call to select() for each buffer when there's already a pending buffer
available to use; in general, avoid system calls entirely when there's data
already waiting, only use system calls when there isn't a completed buffer
to work on next.
- Comments cleanup and some code cleanup.
- A README to provide a little more guidance on getting it working. :-)
You will need to "make clean ; make ; make install" in the modified libpcap
against, as the size of pcap_t has changed. In principle "make ; make
install" should DTRT, but it appears not to for me.
Robert N M Watson
Computer Laboratory
University of Cambridge
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