Commit 94c7eb54 authored Aug 13, 2020 by Eric Dumazet Committed by David S. Miller Aug 13, 2020

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>

parent 96436094

include/trace/events/random.h

+17 −0

Original line number	Diff line number	Diff line
		@@ -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 */

lib/random32.c

+2 −0

Original line number	Diff line number	Diff line
		@@ -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;

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