Paper on device polling and packet capture performance

[Bruce M Simpson]

On Fri, Jan 09, 2004 at 03:51:43PM -0600, Guy Helmer wrote:
> I want to look at memory-mapped access to the BPF device.
> This would preserve the existing network device drivers
> while reducing mbuf copies, context switches/user-kernel
> transitions, and latency.  Performance ought to be
> comparable to Luca's approach, and this would also
> preserve bpf filtering capability.
> 
> (If someone else has already done this, I'd love to
> know where to find the code!)

I did review some patches related to this last month but they weren't
for FreeBSD. One big problem with the approach involved which leapt out
at me was that the space was allocated within user address space, which
introduces the risk of page faults (as you may know we can't ever fault
with a mutex held -- or it's game over).

I'd be happy to review other patches for this. My personal feeling though
is that the actual performance increase may not be that great, but it's
a case of someone implementing it and doing the math.

BMS