On Tue, Dec 20, 2022 at 11:42:46AM +0100, Stefano Brivio wrote: > Sorry for the further delay, > > On Wed, 14 Dec 2022 11:35:46 +0100 > Stefano Brivio wrote: > > > On Wed, 14 Dec 2022 12:42:14 +1100 > > David Gibson wrote: > > > > > On Tue, Dec 13, 2022 at 11:48:47PM +0100, Stefano Brivio wrote: > > > > Sorry for the long delay here, > > > > > > > > On Mon, 5 Dec 2022 19:14:21 +1100 > > > > David Gibson wrote: > > > > > > > > > Usually udp_sock_handler() will receive and forward multiple (up to 32) > > > > > datagrams in udp_sock_handler(), then forward them all to the tap > > > > > interface. For unclear reasons, though, when in pasta mode we will only > > > > > receive and forward a single datagram at a time. Change it to receive > > > > > multiple datagrams at once, like the other paths. > > > > > > > > This is explained in the commit message of 6c931118643c ("tcp, udp: > > > > Receive batching doesn't pay off when writing single frames to tap"). > > > > > > > > I think it's worth re-checking the throughput now as this path is a bit > > > > different, but unfortunately I didn't include this in the "perf" tests :( > > > > because at the time I introduced those I wasn't sure it even made sense to > > > > have traffic from the same host being directed to the tap device. > > > > > > > > The iperf3 runs were I observed this are actually the ones from the Podman > > > > demo. Ideally that case should be also checked in the perf/pasta_udp tests. > > > > > > Hm, ok. > > > > > > > How fundamental is this for the rest of the series? I couldn't find any > > > > actual dependency on this but I might be missing something. > > > > > > So the issue is that prior to this change in pasta we receive multiple > > > frames at once on the splice path, but one frame at a time on the tap > > > path. By the end of this series we can't do that any more, because we > > > don't know before the recvmmsg() which one we'll be doing. > > > > Oh, right, I see. Then let me add this path to the perf/pasta_udp test > > and check how relevant this is now, I'll get back to you in a bit. > > I was checking the wrong path. With this: > > diff --git a/test/perf/pasta_udp b/test/perf/pasta_udp > index 27ea724..973c2f4 100644 > --- a/test/perf/pasta_udp > +++ b/test/perf/pasta_udp > @@ -31,6 +31,14 @@ report pasta lo_udp 1 __FREQ__ > > th MTU 1500B 4000B 16384B 65535B > > +tr UDP throughput over IPv6: host to ns > +nsout IFNAME ip -j link show | jq -rM '.[] | select(.link_type == "ether").ifname' > +nsout ADDR6 ip -j -6 addr show|jq -rM '.[] | select(.ifname == "__IFNAME__").addr_info[] | select(.scope == "global" and .prefixlen == 64).local' > +bw - > +bw - > +bw - > +iperf3 BW host ns __ADDR6__ 100${i}2 __THREADS__ __TIME__ __OPTS__ -b 15G > +bw __BW__ 7.0 9.0 > > tr UDP throughput over IPv6: ns to host > ns ip link set dev lo mtu 1500 > diff --git a/test/run b/test/run > index e07513f..b53182b 100755 > --- a/test/run > +++ b/test/run > @@ -67,6 +67,14 @@ run() { > test build/clang_tidy > teardown build > > + VALGRIND=0 > + setup passt_in_ns > + test passt/ndp > + test passt/dhcp > + test perf/pasta_udp > + test passt_in_ns/shutdown > + teardown passt_in_ns > + > setup pasta > test pasta/ndp > test pasta/dhcp Ah, ok. Can we add that to the standard set of tests ASAP, please. > I get 21.6 gbps after this series, and 29.7 gbps before -- it's quite > significant. Drat. > And there's nothing strange in perf's output, really, the distribution > of overhead per functions is pretty much the same, but writing multiple > messages to the tap device just takes more cycles per message compared > to a single message. That's so weird. It should be basically an identical set of write()s, except that they happen in a batch, rather than a bit spread out. I guess it has to be some kind of cache locality thing. I wonder if the difference would go away or reverse if we had a way to submit multiple frames with a single syscall. > I'm a bit ashamed to propose this, but do you think about something > like: > if (c->mode == MODE_PASTA) { if (recvmmsg(ref.r.s, mmh_recv, > 1, 0, NULL) <= 0) return; > if (udp_mmh_splice_port(v6, mmh_recv)) { n = > recvmmsg(ref.r.s, mmh_recv + 1, UDP_MAX_FRAMES > - 1, 0, NULL); } > if (n > 0) n++; else n = 1; } else { n = > recvmmsg(ref.r.s, mmh_recv, UDP_MAX_FRAMES, 0, > NULL); if (n <= 0) return; } > ? Other than the inherent ugliness, it looks like a good > approximation to me. Hmm. Well, the first question is how much impact does going 1 message at a time have on the spliced throughput. If it's not too bad, then we could just always go one at a time for pasta, regardless of splicing. And we could even abstract that difference into the tap backend with a callback like tap_batch_size(c). -- David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson