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From: Namhyung Kim <namhyung@kernel.org>
To: Wang Nan <wangnan0@huawei.com>
Cc: linux-kernel@vger.kernel.org, kan.liang@intel.com,
	acme@kernel.org, jolsa@redhat.com, kernel-team@lge.com
Subject: Re: [PATCH 1/2] perf mmap: Fix perf backward recording
Date: Wed, 1 Nov 2017 18:49:29 +0900	[thread overview]
Message-ID: <20171101094929.GB25146@danjae.aot.lge.com> (raw)
In-Reply-To: <20171101055327.141281-2-wangnan0@huawei.com>

Hi,

On Wed, Nov 01, 2017 at 05:53:26AM +0000, Wang Nan wrote:
> perf record backward recording doesn't work as we expected: it never
> overwrite when ring buffer full.
> 
> Test:
> 
> (Run a busy printing python task background like this:
> 
>  while True:
>      print 123
> 
> send SIGUSR2 to perf to capture snapshot.)
> 
>  # ./perf record --overwrite -e raw_syscalls:sys_enter -e raw_syscalls:sys_exit --exclude-perf -a --switch-output
>  [ perf record: dump data: Woken up 1 times ]
>  [ perf record: Dump perf.data.2017110101520743 ]
>  [ perf record: dump data: Woken up 1 times ]
>  [ perf record: Dump perf.data.2017110101521251 ]
>  [ perf record: dump data: Woken up 1 times ]
>  [ perf record: Dump perf.data.2017110101521692 ]
>  ^C[ perf record: Woken up 1 times to write data ]
>  [ perf record: Dump perf.data.2017110101521936 ]
>  [ perf record: Captured and wrote 0.826 MB perf.data.<timestamp> ]
> 
>  # ./perf script -i ./perf.data.2017110101520743 | head -n3
>              perf  2717 [000] 12449.310785: raw_syscalls:sys_enter: NR 16 (5, 2400, 0, 59, 100, 0)
>              perf  2717 [000] 12449.310790: raw_syscalls:sys_enter: NR 7 (4112340, 2, ffffffff, 3df, 100, 0)
>            python  2545 [000] 12449.310800:  raw_syscalls:sys_exit: NR 1 = 4
>  # ./perf script -i ./perf.data.2017110101521251 | head -n3
>              perf  2717 [000] 12449.310785: raw_syscalls:sys_enter: NR 16 (5, 2400, 0, 59, 100, 0)
>              perf  2717 [000] 12449.310790: raw_syscalls:sys_enter: NR 7 (4112340, 2, ffffffff, 3df, 100, 0)
>            python  2545 [000] 12449.310800:  raw_syscalls:sys_exit: NR 1 = 4
>  # ./perf script -i ./perf.data.2017110101521692 | head -n3
>              perf  2717 [000] 12449.310785: raw_syscalls:sys_enter: NR 16 (5, 2400, 0, 59, 100, 0)
>              perf  2717 [000] 12449.310790: raw_syscalls:sys_enter: NR 7 (4112340, 2, ffffffff, 3df, 100, 0)
>            python  2545 [000] 12449.310800:  raw_syscalls:sys_exit: NR 1 = 4
> 
> Timestamps are never change, but my background task is a dead loop, can
> easily overwhelme the ring buffer.
> 
> This patch fix it by force unsetting PROT_WRITE for backward ring
> buffer, so all backward ring buffer become overwrite ring buffer.
> 
> Test result:
> 
>  # ./perf record --overwrite -e raw_syscalls:sys_enter -e raw_syscalls:sys_exit --exclude-perf -a --switch-output
>  [ perf record: dump data: Woken up 1 times ]
>  [ perf record: Dump perf.data.2017110101285323 ]
>  [ perf record: dump data: Woken up 1 times ]
>  [ perf record: Dump perf.data.2017110101290053 ]
>  [ perf record: dump data: Woken up 1 times ]
>  [ perf record: Dump perf.data.2017110101290446 ]
>  ^C[ perf record: Woken up 1 times to write data ]
>  [ perf record: Dump perf.data.2017110101290837 ]
>  [ perf record: Captured and wrote 0.826 MB perf.data.<timestamp> ]
>  # ./perf script -i ./perf.data.2017110101285323 | head -n3
>            python  2545 [000] 11064.268083:  raw_syscalls:sys_exit: NR 1 = 4
>            python  2545 [000] 11064.268084: raw_syscalls:sys_enter: NR 1 (1, 12cc330, 4, 7fc237280370, 7fc2373d0700, 2c7b0)
>            python  2545 [000] 11064.268086:  raw_syscalls:sys_exit: NR 1 = 4
>  # ./perf script -i ./perf.data.2017110101290 | head -n3
>  failed to open ./perf.data.2017110101290: No such file or directory
>  # ./perf script -i ./perf.data.2017110101290053 | head -n3
>            python  2545 [000] 11071.564062: raw_syscalls:sys_enter: NR 1 (1, 12cc330, 4, 7fc237280370, 7fc2373d0700, 2c7b0)
>            python  2545 [000] 11071.564064:  raw_syscalls:sys_exit: NR 1 = 4
>            python  2545 [000] 11071.564066: raw_syscalls:sys_enter: NR 1 (1, 12cc330, 4, 7fc237280370, 7fc2373d0700, 2c7b0)
>  # ./perf script -i ./perf.data.2017110101290 | head -n3
>  perf.data.2017110101290053  perf.data.2017110101290446  perf.data.2017110101290837
>  # ./perf script -i ./perf.data.2017110101290446 | head -n3
>              sshd  1321 [000] 11075.499473:  raw_syscalls:sys_exit: NR 14 = 0
>              sshd  1321 [000] 11075.499474: raw_syscalls:sys_enter: NR 14 (2, 7ffe98899490, 0, 8, 0, 3000)
>              sshd  1321 [000] 11075.499474:  raw_syscalls:sys_exit: NR 14 = 0
>  # ./perf script -i ./perf.data.2017110101290837 | head -n3
>            python  2545 [000] 11079.280844:  raw_syscalls:sys_exit: NR 1 = 4
>            python  2545 [000] 11079.280847: raw_syscalls:sys_enter: NR 1 (1, 12cc330, 4, 7fc237280370, 7fc2373d0700, 2c7b0)
>            python  2545 [000] 11079.280850:  raw_syscalls:sys_exit: NR 1 = 4
> 
> Signed-off-by: Wang Nan <wangnan0@huawei.com>
> ---
>  tools/perf/util/evlist.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
> index c6c891e..4c5daba 100644
> --- a/tools/perf/util/evlist.c
> +++ b/tools/perf/util/evlist.c
> @@ -799,22 +799,28 @@ perf_evlist__should_poll(struct perf_evlist *evlist __maybe_unused,
>  }
>  
>  static int perf_evlist__mmap_per_evsel(struct perf_evlist *evlist, int idx,
> -				       struct mmap_params *mp, int cpu_idx,
> +				       struct mmap_params *_mp, int cpu_idx,
>  				       int thread, int *_output, int *_output_backward)
>  {
>  	struct perf_evsel *evsel;
>  	int revent;
>  	int evlist_cpu = cpu_map__cpu(evlist->cpus, cpu_idx);
> +	struct mmap_params *mp;
>  
>  	evlist__for_each_entry(evlist, evsel) {
>  		struct perf_mmap *maps = evlist->mmap;
> +		struct mmap_params rdonly_mp;
>  		int *output = _output;
>  		int fd;
>  		int cpu;
>  
> +		mp = _mp;
>  		if (evsel->attr.write_backward) {
>  			output = _output_backward;
>  			maps = evlist->backward_mmap;
> +			rdonly_mp = *_mp;
> +			rdonly_mp.prot &= ~PROT_WRITE;
> +			mp = &rdonly_mp;
>  
>  			if (!maps) {
>  				maps = perf_evlist__alloc_mmap(evlist);
> -- 

What about this instead (not tested)?


diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
index c6c891e154a6..27ebe355e794 100644
--- a/tools/perf/util/evlist.c
+++ b/tools/perf/util/evlist.c
@@ -838,6 +838,11 @@ static int perf_evlist__mmap_per_evsel(struct perf_evlist *evlist, int idx,
                if (*output == -1) {
                        *output = fd;
 
+                       if (evsel->attr.write_backward)
+                               mp->prot = PROT_READ;
+                       else
+                               mp->prot = PROT_READ | PROT_WRITE;
+
                        if (perf_mmap__mmap(&maps[idx], mp, *output)  < 0)
                                return -1;
                } else {
@@ -1058,9 +1063,7 @@ int perf_evlist__mmap_ex(struct perf_evlist *evlist, unsigned int pages,
        struct perf_evsel *evsel;
        const struct cpu_map *cpus = evlist->cpus;
        const struct thread_map *threads = evlist->threads;
-       struct mmap_params mp = {
-               .prot = PROT_READ | (overwrite ? 0 : PROT_WRITE),
-       };
+       struct mmap_params mp;
 
        if (!evlist->mmap)
                evlist->mmap = perf_evlist__alloc_mmap(evlist);

  reply	other threads:[~2017-11-01  9:51 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-11-01  5:53 [PATCH 0/2] perf record: Fix --overwrite and clarify concepts Wang Nan
2017-11-01  5:53 ` [PATCH 1/2] perf mmap: Fix perf backward recording Wang Nan
2017-11-01  9:49   ` Namhyung Kim [this message]
2017-11-01 10:32     ` Wangnan (F)
2017-11-01 12:00       ` Namhyung Kim
2017-11-01 12:10         ` Wangnan (F)
2017-11-01 12:39           ` Jiri Olsa
2017-11-01 12:56             ` Wangnan (F)
2017-11-02 15:12               ` Jiri Olsa
2017-11-01 13:57           ` Liang, Kan
2017-11-01 16:12             ` Wangnan (F)
2017-11-01 16:22               ` Liang, Kan
2017-11-02  5:34                 ` Namhyung Kim
2017-11-02 13:25                   ` Liang, Kan
2017-11-02 14:59                     ` Jiri Olsa
2017-11-01  5:53 ` [PATCH 2/2] perf record: Replace 'overwrite' by 'flightrecorder' for better naming Wang Nan
2017-11-01 10:03   ` Namhyung Kim
2017-11-01 10:17     ` Wangnan (F)
2017-11-01 12:03       ` Namhyung Kim
2017-11-01 13:26   ` Liang, Kan
2017-11-01 14:05     ` Wangnan (F)
2017-11-01 14:22       ` Liang, Kan
2017-11-01 14:44         ` Wangnan (F)
2017-11-01 15:04           ` Liang, Kan
2017-11-01 16:00             ` Wangnan (F)
2017-11-01 16:13               ` Liang, Kan

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