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SubjectRe: [PATCH v2 net-next] net: introduce a new tracepoint for tcp_rcv_space_adjust
On Wed, Apr 18, 2018 at 1:27 AM, Eric Dumazet <eric.dumazet@gmail.com> wrote:
>
>
> 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 :/
>

Sorry for the poor expression. Will improve it.
I mean with these two tracepoint we could calculate the latency that
if the user process can't process this packet immdiately.

>>
>> 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);
>
> 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)
>

Will improve.

>> ),
>>
>> - 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.
>

OK

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