netdev - Re: [PATCH net] random32: add a tracepoint for prandom

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Date:   Thu, 13 Aug 2020 19:53:11 +0200
From:   Sedat Dilek <sedat.dilek@...il.com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <eric.dumazet@...il.com>, Willy Tarreau <w@....eu>
Subject: Re: [PATCH net] random32: add a tracepoint for prandom_u32()

On Thu, Aug 13, 2020 at 7:06 PM Eric Dumazet <edumazet@...gle.com> wrote:
>
> There has been some heat around prandom_u32() lately, and some people
> were wondering if there was a simple way to determine how often
> it was used, before considering making it maybe 10 times more expensive.
>
> This tracepoint exports the generated pseudo random value.
>
> Tested:
>
> perf list | grep prandom_u32
>   random:prandom_u32                                 [Tracepoint event]
>
> perf record -a [-g] [-C1] -e random:prandom_u32 sleep 1
> [ perf record: Woken up 0 times to write data ]
> [ perf record: Captured and wrote 259.748 MB perf.data (924087 samples) ]
>
> perf report --nochildren
>     ...
>     97.67%  ksoftirqd/1     [kernel.vmlinux]  [k] prandom_u32
>             |
>             ---prandom_u32
>                prandom_u32
>                |
>                |--48.86%--tcp_v4_syn_recv_sock
>                |          tcp_check_req
>                |          tcp_v4_rcv
>                |          ...
>                 --48.81%--tcp_conn_request
>                           tcp_v4_conn_request
>                           tcp_rcv_state_process
>                           ...
> perf script
>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Cc: Willy Tarreau <w@....eu>
> Cc: Sedat Dilek <sedat.dilek@...il.com>

Thanks for the patch and embedding a list of instructions with linux-perf.

Tested-by: Sedat Dilek <sedat.dilek@...il.com>

- Sedat -

> ---
> According to MAINTAINERS, lib/random32.c is part of networking...
>
>  include/trace/events/random.h | 17 +++++++++++++++++
>  lib/random32.c                |  2 ++
>  2 files changed, 19 insertions(+)
>
> diff --git a/include/trace/events/random.h b/include/trace/events/random.h
> index 32c10a515e2d5438e8d620a0c2313aab5f849b2b..9570a10cb949b5792c4290ba8e82a077ac655069 100644
> --- a/include/trace/events/random.h
> +++ b/include/trace/events/random.h
> @@ -307,6 +307,23 @@ TRACE_EVENT(urandom_read,
>                   __entry->pool_left, __entry->input_left)
>  );
>
> +TRACE_EVENT(prandom_u32,
> +
> +       TP_PROTO(unsigned int ret),
> +
> +       TP_ARGS(ret),
> +
> +       TP_STRUCT__entry(
> +               __field(   unsigned int, ret)
> +       ),
> +
> +       TP_fast_assign(
> +               __entry->ret = ret;
> +       ),
> +
> +       TP_printk("ret=%u" , __entry->ret)
> +);
> +
>  #endif /* _TRACE_RANDOM_H */
>
>  /* This part must be outside protection */
> diff --git a/lib/random32.c b/lib/random32.c
> index 3d749abb9e80d54d8e330e07fb8b773b7bec2b83..932345323af092a93fc2690b0ebbf4f7485ae4f3 100644
> --- a/lib/random32.c
> +++ b/lib/random32.c
> @@ -39,6 +39,7 @@
>  #include <linux/random.h>
>  #include <linux/sched.h>
>  #include <asm/unaligned.h>
> +#include <trace/events/random.h>
>
>  #ifdef CONFIG_RANDOM32_SELFTEST
>  static void __init prandom_state_selftest(void);
> @@ -82,6 +83,7 @@ u32 prandom_u32(void)
>         u32 res;
>
>         res = prandom_u32_state(state);
> +       trace_prandom_u32(res);
>         put_cpu_var(net_rand_state);
>
>         return res;
> --
> 2.28.0.220.ged08abb693-goog
>