Hi Phil, On Fri, Oct 02, 2020 at 11:00:33AM +0200, Phil Sutter wrote: > Hi Florian, > > On Fri, Oct 02, 2020 at 12:25:36AM +0200, Florian Westphal wrote: > > Phil Sutter <phil@xxxxxx> wrote: > > > The following two patches improve packet throughput in a test setup > > > sending UDP packets (using iperf3) between two netns. The ruleset used > > > on receiver side is like this: > > > > > > | *filter > > > | :test - [0:0] > > > | -A INPUT -j test > > > | -A INPUT -j ACCEPT > > > | -A test ! -s 10.0.0.0/10 -j DROP # this line repeats 10000 times > > > | COMMIT > > > > > > These are the generated VM instructions for each rule: > > > > > > | [ payload load 4b @ network header + 12 => reg 1 ] > > > | [ bitwise reg 1 = (reg=1 & 0x0000c0ff ) ^ 0x00000000 ] > > > > Not related to this patch, but we should avoid the bitop if the > > netmask is divisble by 8 (can adjust the cmp -- adjusting the > > payload expr is probably not worth it). > > See the patch I just sent to this list. I adjusted both - it simply > didn't appear to me that I could get by with reducing the cmp expression > size only. The upside though is that detecting the prefix match based on > payload expression length is quick and easy. > > Someone will have to adjust nft tool, though. ;) > > > > | [ cmp eq reg 1 0x0000000a ] > > > | [ counter pkts 0 bytes 0 ] > > > > Out of curiosity, does omitting 'counter' help? > > > > nft counter is rather expensive due to bh disable, > > iptables does it once at the evaluation loop only. > > I changed the test to create the base ruleset using iptables-nft-restore > just as before, but create the rules in 'test' chain like so: > > | nft add rule filter test ip saddr != 10.0.0.0/10 drop > > The VM code is as expected: > > | [ payload load 4b @ network header + 12 => reg 1 ] > | [ bitwise reg 1 = (reg=1 & 0x0000c0ff ) ^ 0x00000000 ] > | [ cmp eq reg 1 0x0000000a ] > | [ immediate reg 0 drop ] > > Performance is ~7000pkt/s. So while it's faster than iptables-nft, it's > still quite a bit slower than legacy iptables despite the skipped > counters. iptables is optimized for matching on input/output device name and IPv4 address + mask (see ip_packet_match()) for historical reasons, iptables does not use a match for this since the beginning. One possibility (in the short-term) is to add an internal kernel expression to achieve the same behaviour. The kernel needs to detects for: payload (nh, offset to ip saddr or ip daddr or ip protocol) + cmp payload (nh, offset to ip saddr or ip daddr) + bitwise + cmp meta (iifname or oifname) + bitwise + cmp meta (iifname or oifname) + cmp at the very beginning of the rule. and squash these expressions into the "built-in" iptables match expression which emulates ip_packet_match(). Not nice, but if microbenchmarks using thousand of rules really matter (this is worst case O(n) linear list evaluation...) then it might make sense to explore this.
