random32: add a tracepoint for prandom_u32()

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@google.com>
Cc: Willy Tarreau <w@1wt.eu>
Cc: Sedat Dilek <sedat.dilek@gmail.com>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 17 insertions, 0 deletions

diff --git a/include/trace/events/random.h b/include/trace/events/random.h
index 32c10a515e2d..9570a10cb949 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 */