On 04/17/2018 09:36 AM, Yafang Shao 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
Sorry, I could not parse these :/
>
> 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.s...@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);
Please scrap this comment and simply use the real thing.
_entry->sock_cookie = sock_gen_cookie(sk);
We build generic events.
Being able to filter many TCP events on one socket cookie will be useful
If you worry about sock_gen_cookie(sk) being too expensive, then we can add an
inline helper
for the fast path (when sk_cookie has been already set)
> ),
>
> - 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",
iproute2/ss command uses hexadcimal output for socket cookie. Please use %llx
for consistency.
