Commits
Wang Nan committed 71f566a3498
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.<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 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.<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>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Kan Liang <kan.liang@intel.com>
Cc: Mengting Zhang <zhangmengting@huawei.com>
Link: http://lkml.kernel.org/r/20171204165107.95327-2-wangnan0@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>