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random32: add a tracepoint for prandom_u32()

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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>
This commit is contained in:
Eric Dumazet 2020-08-13 10:06:43 -07:00 committed by David S. Miller
parent 9643609423
commit 94c7eb54c4
2 changed files with 19 additions and 0 deletions
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17
include/trace/events/random.h
View File

@ -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 */

2
lib/random32.c
View File

@ -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;