From 71f566a34986f4a86a8c546c7a36f70f0132b8a9 Mon Sep 17 00:00:00 2001 From: Wang Nan Date: Mon, 4 Dec 2017 16:51:05 +0000 Subject: perf mmap: Fix perf backward recording 'perf record' backward recording doesn't work as we expected: it never overwrites when ring buffer gets full. Test: Run a busy python printing task background like this: while True: print 123 send SIGUSR2 to perf to capture snapshot, then: # ./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. ] # ./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 never change, but my background task is a dead loop, can easily overwhelm the ring buffer. This patch fixes it by forcing unsetting PROT_WRITE for a backward ring buffer, so all backward ring buffers become overwrite ring buffers. 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. ] # ./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 Acked-by: Namhyung Kim Cc: Jiri Olsa Cc: Kan Liang Cc: Mengting Zhang Link: http://lkml.kernel.org/r/20171204165107.95327-2-wangnan0@huawei.com Signed-off-by: Arnaldo Carvalho de Melo --- tools/perf/util/evlist.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-) (limited to 'tools/perf/util/evlist.c') diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c index 68c1f9546650..b1cea711232b 100644 --- a/tools/perf/util/evlist.c +++ b/tools/perf/util/evlist.c @@ -812,6 +812,7 @@ static int perf_evlist__mmap_per_evsel(struct perf_evlist *evlist, int idx, int fd; int cpu; + mp->prot = PROT_READ | PROT_WRITE; if (evsel->attr.write_backward) { output = _output_backward; maps = evlist->backward_mmap; @@ -824,6 +825,7 @@ static int perf_evlist__mmap_per_evsel(struct perf_evlist *evlist, int idx, if (evlist->bkw_mmap_state == BKW_MMAP_NOTREADY) perf_evlist__toggle_bkw_mmap(evlist, BKW_MMAP_RUNNING); } + mp->prot &= ~PROT_WRITE; } if (evsel->system_wide && thread) @@ -1058,9 +1060,12 @@ 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 | PROT_WRITE, - }; + /* + * Delay setting mp.prot: set it before calling perf_mmap__mmap. + * Its value is decided by evsel's write_backward. + * So &mp should not be passed through const pointer. + */ + struct mmap_params mp; if (!evlist->mmap) evlist->mmap = perf_evlist__alloc_mmap(evlist); -- cgit v1.2.3