Date: Wed, 16 Jun 2004 17:38:48 +0300 From: Sergey Lyubka <devnull@uptsoft.com> To: freebsd-hackers@freebsd.org Subject: Re: memory mapped packet capturing - bpf replacement ? Message-ID: <20040616173848.A8939@oasis.uptsoft.com> In-Reply-To: <FE045D4D9F7AED4CBFF1B3B813C8533701BD40C7@mail.sandvine.com>; from emaste@sandvine.com on Mon, Jun 14, 2004 at 08:38:57AM -0400 References: <FE045D4D9F7AED4CBFF1B3B813C8533701BD40C7@mail.sandvine.com>
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> Does the ng_hub cause the packet to be copied? If so you've > still got the same number of copies as vanilla BPF. ng_hub does copy a packets. But, this does not explain the test results. the benchmark works like this: 1. connect ng_mmq node to ng_hub 2. run benchmark for mmq 3. open pcap device (mmq node still connected) 4. run benchmark for pcap (mmq node still connected) so, ng_mmq and ng_hub are working during pcap benchmark, so additional copies do not explain it. the strange thing is: why bpf, which does context switches, works more efficiently than grabbing packets directly from memory mapped chunk ? did I overlook something significant ? I was thinking that while application spins awaiting data, scheduler may detach it from the CPU, and then ringbuffer may be overflown. I increased the priority to ridiculous values, and increased ringbuffer size to as large as 32 Megabytes. The best I got is the same results as pcap. Can anybody explain this ? Example test, moderate traffic generated by the ping -f: # ./benchmark rl0 /dev/mmq16 10000 desc rcvd dropped seen totlen pps time (sec) mmq 10784 770 10000 13420000 10076 1.070 pcap 10016 0 10000 13420000 9093 1.102
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