HEADS UP: zerocopy bpf commits impending
rwatson at FreeBSD.org
Mon Mar 24 07:15:53 PDT 2008
On Mon, 24 Mar 2008, Christian S.J. Peron wrote:
> I just want everyone to know that I have completed the zerocopy bpf commit.
> Please be on the "lookout" for any strange bpf related issues.
> For people that want to test the new zerocopy bpf implementation, a patch
> can be found here:
> Any comments, patches etc can be sent to Robert Watson (rwatson@) or myself.
FYI, right now there is a known issue in which only one of the two BPF buffers
can be owned by user processes at a time. As a result, when acking one
buffer, it's almost always the case that userspace will enter select() even
though another buffer is essentially ready, leading to a system call being
generated for each buffer even though that's undesirable. I'm working on some
changing allowing both buffers to be owned by userspace at a time, but it will
be a couple of weeks before that enters CVS. I believe that the current
libpcap patches should keep working with that fine, although of course, we'll
see. :-) The bpf.4 documentation is very careful to warn that applications
should not assume that there are any invariants about the number of buffers
assigned to userspace at a time.
Robert N M Watson
University of Cambridge
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