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Message-ID: <CANn89i+kcnSDTJ5E5Rrmvk-V3Oqg8NbAyG=LWWVLc+_CF_kLjA@mail.gmail.com> Date: Tue, 17 Oct 2023 14:08:52 +0200 From: Eric Dumazet <edumazet@...gle.com> To: Stefan Wahren <wahrenst@....net> Cc: Neal Cardwell <ncardwell@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Fabio Estevam <festevam@...il.com>, linux-imx@....com, Stefan Wahren <stefan.wahren@...rgebyte.com>, Michael Heimpold <mhei@...mpold.de>, netdev@...r.kernel.org, Yuchung Cheng <ycheng@...gle.com> Subject: Re: iperf performance regression since Linux 5.18 On Tue, Oct 17, 2023 at 11:53 AM Stefan Wahren <wahrenst@....net> wrote: > > Hi Eric, > > Am 16.10.23 um 20:47 schrieb Eric Dumazet: > > On Mon, Oct 16, 2023 at 8:25 PM Stefan Wahren <wahrenst@....net> wrote: > >> Hi Eric, > >> > >> Am 16.10.23 um 12:35 schrieb Eric Dumazet: > >>> On Mon, Oct 16, 2023 at 11:49 AM Eric Dumazet <edumazet@...gle.com> wrote: > >>> Speaking of TSQ, it seems an old change (commit 75eefc6c59fd "tcp: > >>> tsq: add a shortcut in tcp_small_queue_check()") > >>> has been accidentally removed in 2017 (75c119afe14f "tcp: implement > >>> rb-tree based retransmit queue") > >>> > >>> Could you try this fix: > >>> > >>> diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c > >>> index 9c8c42c280b7638f0f4d94d68cd2c73e3c6c2bcc..e61a3a381d51b554ec8440928e22a290712f0b6b > >>> 100644 > >>> --- a/net/ipv4/tcp_output.c > >>> +++ b/net/ipv4/tcp_output.c > >>> @@ -2542,6 +2542,18 @@ static bool tcp_pacing_check(struct sock *sk) > >>> return true; > >>> } > >>> > >>> +static bool tcp_rtx_queue_empty_or_single_skb(const struct sock *sk) > >>> +{ > >>> + const struct rb_node *node = sk->tcp_rtx_queue.rb_node; > >>> + > >>> + /* No skb in the rtx queue. */ > >>> + if (!node) > >>> + return true; > >>> + > >>> + /* Only one skb in rtx queue. */ > >>> + return !node->rb_left && !node->rb_right; > >>> +} > >>> + > >>> /* TCP Small Queues : > >>> * Control number of packets in qdisc/devices to two packets / or ~1 ms. > >>> * (These limits are doubled for retransmits) > >>> @@ -2579,12 +2591,12 @@ static bool tcp_small_queue_check(struct sock > >>> *sk, const struct sk_buff *skb, > >>> limit += extra_bytes; > >>> } > >>> if (refcount_read(&sk->sk_wmem_alloc) > limit) { > >>> - /* Always send skb if rtx queue is empty. > >>> + /* Always send skb if rtx queue is empty or has one skb. > >>> * No need to wait for TX completion to call us back, > >>> * after softirq/tasklet schedule. > >>> * This helps when TX completions are delayed too much. > >>> */ > >>> - if (tcp_rtx_queue_empty(sk)) > >>> + if (tcp_rtx_queue_empty_or_single_skb(sk)) > >>> return false; > >>> > >>> set_bit(TSQ_THROTTLED, &sk->sk_tsq_flags); > >> This patch applied on top of Linux 6.1.49, TSO on, gso_max_size 65535, > >> CONFIG_HZ_100=y > >> > >> root@...ragon:/boot# iperf -t 10 -i 1 -c 192.168.1.129 > >> ------------------------------------------------------------ > >> Client connecting to 192.168.1.129, TCP port 5001 > >> TCP window size: 192 KByte (default) > >> ------------------------------------------------------------ > >> [ 3] local 192.168.1.12 port 59714 connected with 192.168.1.129 port 5001 > >> [ ID] Interval Transfer Bandwidth > >> [ 3] 0.0- 1.0 sec 11.5 MBytes 96.5 Mbits/sec > >> [ 3] 1.0- 2.0 sec 11.4 MBytes 95.4 Mbits/sec > >> [ 3] 2.0- 3.0 sec 11.1 MBytes 93.3 Mbits/sec > >> [ 3] 3.0- 4.0 sec 11.2 MBytes 94.4 Mbits/sec > >> [ 3] 4.0- 5.0 sec 11.1 MBytes 93.3 Mbits/sec > >> [ 3] 5.0- 6.0 sec 11.2 MBytes 94.4 Mbits/sec > >> [ 3] 6.0- 7.0 sec 11.2 MBytes 94.4 Mbits/sec > >> [ 3] 7.0- 8.0 sec 11.1 MBytes 93.3 Mbits/sec > >> [ 3] 8.0- 9.0 sec 11.4 MBytes 95.4 Mbits/sec > >> [ 3] 9.0-10.0 sec 11.2 MBytes 94.4 Mbits/sec > >> [ 3] 0.0-10.0 sec 113 MBytes 94.4 Mbits/sec > >> > >> The figures are comparable to disabling TSO -> Good > >> > >> Thanks > > Great. I suspect a very slow TX completion from fec then. > > > > Could you use the following bpftrace program while your iperf is running ? > unfortuntely there is no bpftrace and most of its dependencies on my > platform. I looked at some guides and it seems to have a lot of (build) > dependencies. On a PC this won't be a problem, but on my ARM platform > there is only 1 GB eMMC space left. > > Before investing a lot of time to get bpftrace running, is there an > alternative solution? No worries Stefan, I think we do not have to get precise numbers, I will try to provide a debug patch (since you are able to build custom kernels) In the meantime, I will submit the official TCP patch, as you said it was helping a lot. Just to confirm, have you tried the patch on top of the latest net tree ? Thanks. > > > > .bpftrace -e ' > > k:__dev_queue_xmit { > > $skb = (struct sk_buff *)arg0; > > if ($skb->fclone == 2) { > > @start[$skb] = nsecs; > > } > > } > > k:__kfree_skb { > > $skb = (struct sk_buff *)arg0; > > if ($skb->fclone == 2 && @start[$skb]) { > > @tx_compl_usecs = hist((nsecs - @start[$skb])/1000); > > delete(@start[$skb]); > > } > > } > > END { clear(@start); }' >
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