| Message ID | 20240510155900.1825946-2-zijianzhang@bytedance.com (mailing list archive) |
|---|---|
| State | Superseded |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | net: A lightweight zero-copy notification | expand |
zijianzhang@ wrote: > From: Zijian Zhang <zijianzhang@bytedance.com> > > In selftests/net/msg_zerocopy.c, it has a while loop keeps calling sendmsg > on a socket with MSG_ZEROCOPY flag, and it will recv the notifications > until the socket is not writable. Typically, it will start the receiving > process after around 30+ sendmsgs. However, because of the > commit dfa2f0483360 ("tcp: get rid of sysctl_tcp_adv_win_scale") > the sender is always writable and does not get any chance to run recv > notifications. The selftest always exits with OUT_OF_MEMORY because the > memory used by opt_skb exceeds the core.sysctl_optmem_max. > > According to our experiments, this problem can be mitigated by open the > DEBUG_LOCKDEP configuration for the kernel. But it will makes the > notifications disordered even in good commits before > commit dfa2f0483360 ("tcp: get rid of sysctl_tcp_adv_win_scale"). > > We introduce "cfg_notification_limit" to force sender to receive > notifications after some number of sendmsgs. And, notifications may not > come in order, because of the reason we present above. We have order > checking code managed by cfg_verbose. > > Signed-off-by: Zijian Zhang <zijianzhang@bytedance.com> > Signed-off-by: Xiaochun Lu <xiaochun.lu@bytedance.com> > --- > tools/testing/selftests/net/msg_zerocopy.c | 15 +++++++++++++-- > 1 file changed, 13 insertions(+), 2 deletions(-) > > diff --git a/tools/testing/selftests/net/msg_zerocopy.c b/tools/testing/selftests/net/msg_zerocopy.c > index bdc03a2097e8..ba6c257f689c 100644 > --- a/tools/testing/selftests/net/msg_zerocopy.c > +++ b/tools/testing/selftests/net/msg_zerocopy.c > @@ -85,6 +85,7 @@ static bool cfg_rx; > static int cfg_runtime_ms = 4200; > static int cfg_verbose; > static int cfg_waittime_ms = 500; > +static int cfg_notification_limit = 32; > static bool cfg_zerocopy; > > static socklen_t cfg_alen; > @@ -95,6 +96,8 @@ static char payload[IP_MAXPACKET]; > static long packets, bytes, completions, expected_completions; > static int zerocopied = -1; > static uint32_t next_completion; > +/* The number of sendmsgs which have not received notified yet */ > +static uint32_t sendmsg_counter; minor: comment typo. Consider a more self documenting variable and drop the comment static int sends_since_notify;
diff --git a/tools/testing/selftests/net/msg_zerocopy.c b/tools/testing/selftests/net/msg_zerocopy.c index bdc03a2097e8..ba6c257f689c 100644 --- a/tools/testing/selftests/net/msg_zerocopy.c +++ b/tools/testing/selftests/net/msg_zerocopy.c @@ -85,6 +85,7 @@ static bool cfg_rx; static int cfg_runtime_ms = 4200; static int cfg_verbose; static int cfg_waittime_ms = 500; +static int cfg_notification_limit = 32; static bool cfg_zerocopy; static socklen_t cfg_alen; @@ -95,6 +96,8 @@ static char payload[IP_MAXPACKET]; static long packets, bytes, completions, expected_completions; static int zerocopied = -1; static uint32_t next_completion; +/* The number of sendmsgs which have not received notified yet */ +static uint32_t sendmsg_counter; static unsigned long gettimeofday_ms(void) { @@ -208,6 +211,7 @@ static bool do_sendmsg(int fd, struct msghdr *msg, bool do_zerocopy, int domain) error(1, errno, "send"); if (cfg_verbose && ret != len) fprintf(stderr, "send: ret=%u != %u\n", ret, len); + sendmsg_counter++; if (len) { packets++; @@ -435,7 +439,7 @@ static bool do_recv_completion(int fd, int domain) /* Detect notification gaps. These should not happen often, if at all. * Gaps can occur due to drops, reordering and retransmissions. */ - if (lo != next_completion) + if (cfg_verbose && lo != next_completion) fprintf(stderr, "gap: %u..%u does not append to %u\n", lo, hi, next_completion); next_completion = hi + 1; @@ -460,6 +464,7 @@ static bool do_recv_completion(int fd, int domain) static void do_recv_completions(int fd, int domain) { while (do_recv_completion(fd, domain)) {} + sendmsg_counter = 0; } /* Wait for all remaining completions on the errqueue */ @@ -549,6 +554,9 @@ static void do_tx(int domain, int type, int protocol) else do_sendmsg(fd, &msg, cfg_zerocopy, domain); + if (cfg_zerocopy && sendmsg_counter >= cfg_notification_limit) + do_recv_completions(fd, domain); + while (!do_poll(fd, POLLOUT)) { if (cfg_zerocopy) do_recv_completions(fd, domain); @@ -708,7 +716,7 @@ static void parse_opts(int argc, char **argv) cfg_payload_len = max_payload_len; - while ((c = getopt(argc, argv, "46c:C:D:i:mp:rs:S:t:vz")) != -1) { + while ((c = getopt(argc, argv, "46c:C:D:i:l:mp:rs:S:t:vz")) != -1) { switch (c) { case '4': if (cfg_family != PF_UNSPEC) @@ -736,6 +744,9 @@ static void parse_opts(int argc, char **argv) if (cfg_ifindex == 0) error(1, errno, "invalid iface: %s", optarg); break; + case 'l': + cfg_notification_limit = strtoul(optarg, NULL, 0); + break; case 'm': cfg_cork_mixed = true; break;