Messages in this thread | | | From | Yafang Shao <> | Date | Wed, 18 Apr 2018 05:54:55 +0800 | Subject | Re: [PATCH v2 net-next] net: introduce a new tracepoint for tcp_rcv_space_adjust |
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On Wed, Apr 18, 2018 at 1:38 AM, Song Liu <songliubraving@fb.com> wrote: > > >> On Apr 17, 2018, at 9:36 AM, Yafang Shao <laoar.shao@gmail.com> wrote: >> >> tcp_rcv_space_adjust is called every time data is copied to user space, >> introducing a tcp tracepoint for which could show us when the packet is >> copied to user. >> This could help us figure out whether there's latency in user process. >> >> When a tcp packet arrives, tcp_rcv_established() will be called and with >> the existed tracepoint tcp_probe we could get the time when this packet >> arrives. >> Then this packet will be copied to user, and tcp_rcv_space_adjust will >> be called and with this new introduced tracepoint we could get the time >> when this packet is copied to user. >> >> arrives time : user process time => latency caused by user >> tcp_probe tcp_rcv_space_adjust >> >> Hence in the printk message, sk_cookie is printed as a key to relate >> tcp_rcv_space_adjust with tcp_probe. >> >> Maybe we could export sockfd in this new tracepoint as well, then we >> could relate this new tracepoint with epoll/read/recv* tracepoints, and >> finally that could show us the whole lifespan of this packet. But we >> could also implement that with pid as these functions are executed in >> process context. >> >> Signed-off-by: Yafang Shao <laoar.shao@gmail.com> >> >> --- >> v1 -> v2: use sk_cookie as key suggested by Eric. >> --- >> include/trace/events/tcp.h | 33 +++++++++++++++++++++++++++------ >> net/ipv4/tcp_input.c | 2 ++ >> 2 files changed, 29 insertions(+), 6 deletions(-) >> >> diff --git a/include/trace/events/tcp.h b/include/trace/events/tcp.h >> index 3dd6802..814f754 100644 >> --- a/include/trace/events/tcp.h >> +++ b/include/trace/events/tcp.h >> @@ -10,6 +10,7 @@ >> #include <linux/tracepoint.h> >> #include <net/ipv6.h> >> #include <net/tcp.h> >> +#include <linux/sock_diag.h> >> >> #define TP_STORE_V4MAPPED(__entry, saddr, daddr) \ >> do { \ >> @@ -125,6 +126,7 @@ >> __array(__u8, daddr, 4) >> __array(__u8, saddr_v6, 16) >> __array(__u8, daddr_v6, 16) >> + __field(__u64, sock_cookie) >> ), >> >> TP_fast_assign( >> @@ -144,12 +146,24 @@ >> >> TP_STORE_ADDRS(__entry, inet->inet_saddr, inet->inet_daddr, >> sk->sk_v6_rcv_saddr, sk->sk_v6_daddr); >> + >> + /* >> + * sk_cookie is used to identify a socket, with which we could >> + * relate this tracepoint with other tracepoints, >> + * i.e. tcp_probe. >> + * If we needn't this relation, then sk_cookie is useless; >> + * if we need this relation, then tcp_probe is already set, >> + * and sk_cookie is already set in tcp_probe, so we could get >> + * the value directly. >> + */ >> + __entry->sock_cookie = atomic64_read(&sk->sk_cookie); >> ), >> >> - TP_printk("sport=%hu dport=%hu saddr=%pI4 daddr=%pI4 saddrv6=%pI6c daddrv6=%pI6c", >> + TP_printk("sport=%hu dport=%hu saddr=%pI4 daddr=%pI4 saddrv6=%pI6c daddrv6=%pI6c sock_cookie=%llu", >> __entry->sport, __entry->dport, >> __entry->saddr, __entry->daddr, >> - __entry->saddr_v6, __entry->daddr_v6) >> + __entry->saddr_v6, __entry->daddr_v6, >> + __entry->sock_cookie) >> ); >> >> DEFINE_EVENT(tcp_event_sk, tcp_receive_reset, >> @@ -166,6 +180,13 @@ >> TP_ARGS(sk) >> ); >> >> +DEFINE_EVENT(tcp_event_sk, tcp_rcv_space_adjust, >> + >> + TP_PROTO(const struct sock *sk), >> + >> + TP_ARGS(sk) >> +); >> + >> TRACE_EVENT(tcp_retransmit_synack, >> >> TP_PROTO(const struct sock *sk, const struct request_sock *req), >> @@ -232,6 +253,7 @@ >> __field(__u32, snd_wnd) >> __field(__u32, srtt) >> __field(__u32, rcv_wnd) >> + __field(__u64, sock_cookie) >> ), >> >> TP_fast_assign( >> @@ -256,15 +278,14 @@ >> __entry->rcv_wnd = tp->rcv_wnd; >> __entry->ssthresh = tcp_current_ssthresh(sk); >> __entry->srtt = tp->srtt_us >> 3; >> + __entry->sock_cookie = sock_gen_cookie(sk); >> ), >> >> - TP_printk("src=%pISpc dest=%pISpc mark=%#x length=%d snd_nxt=%#x " >> - "snd_una=%#x snd_cwnd=%u ssthresh=%u snd_wnd=%u srtt=%u " >> - "rcv_wnd=%u", >> + TP_printk("src=%pISpc dest=%pISpc mark=%#x length=%d snd_nxt=%#x snd_una=%#x snd_cwnd=%u ssthresh=%u snd_wnd=%u srtt=%u rcv_wnd=%u sock_cookie=%llu", >> __entry->saddr, __entry->daddr, __entry->mark, >> __entry->length, __entry->snd_nxt, __entry->snd_una, >> __entry->snd_cwnd, __entry->ssthresh, __entry->snd_wnd, >> - __entry->srtt, __entry->rcv_wnd) >> + __entry->srtt, __entry->rcv_wnd, __entry->sock_cookie) >> ); >> >> #endif /* _TRACE_TCP_H */ >> diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c >> index f93687f..43ad468 100644 >> --- a/net/ipv4/tcp_input.c >> +++ b/net/ipv4/tcp_input.c >> @@ -582,6 +582,8 @@ void tcp_rcv_space_adjust(struct sock *sk) >> u32 copied; >> int time; >> >> + trace_tcp_rcv_space_adjust(sk); >> + >> tcp_mstamp_refresh(tp); >> time = tcp_stamp_us_delta(tp->tcp_mstamp, tp->rcvq_space.time); >> if (time < (tp->rcv_rtt_est.rtt_us >> 3) || tp->rcv_rtt_est.rtt_us == 0) >> -- >> 1.8.3.1 >> > > If I understand this correctly, you can get all the information you need with > a kprobe on tcp_rcv_space_adjust(). Why is it necessary to introduce a new > tracepoint? >
Tracepoint is less expensive and more cnovinient, that is the same reason why tcp_probe.c was removed and tcp_probe tracepoint was introduced.
Thanks Yafang
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