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authorWang Nan <wangnan0@huawei.com>2016-07-14 08:34:47 +0000
committerArnaldo Carvalho de Melo <acme@redhat.com>2016-07-15 17:27:52 -0300
commit4ea648aec01982d5a57816a95c4665d6081e78f9 (patch)
tree7aabc47adaca3014da0e3e9b53bd645d2b461fcc /tools/perf/perf.h
parentf06149c0db430d3694d601df126b0944cc0156a6 (diff)
perf record: Add --tail-synthesize option
When working with overwritable ring buffer there's a inconvenience problem: if perf dumps data after a long period after it starts, non-sample events may lost, which makes following 'perf report' unable to identify proc name and mmap layout. For example: # perf record -m 4 -e raw_syscalls:* -g --overwrite --switch-output \ dd if=/dev/zero of=/dev/null send SIGUSR2 after dd runs long enough. The resuling perf.data lost correct comm and mmap events: # perf script -i perf.data.2016061522374354 perf 24478 [004] 2581325.601789: raw_syscalls:sys_exit: NR 0 = 512 ^^^^ Should be 'dd' 27b2e8 syscall_slow_exit_work+0xfe2000e3 (/lib/modules/4.6.0-rc3+/build/vmlinux) 203cc7 do_syscall_64+0xfe200117 (/lib/modules/4.6.0-rc3+/build/vmlinux) b18d83 return_from_SYSCALL_64+0xfe200000 (/lib/modules/4.6.0-rc3+/build/vmlinux) 7f47c417edf0 [unknown] ([unknown]) ^^^^^^^^^^^^ Fail to unwind This patch provides a '--tail-synthesize' option, allows perf to collect system status when finalizing output file. In resuling output file, the non-sample events reflect system status when dumping data. After this patch: # perf record -m 4 -e raw_syscalls:* -g --overwrite --switch-output --tail-synthesize \ dd if=/dev/zero of=/dev/null # perf script -i perf.data.2016061600544998 dd 27364 [004] 2583244.994464: raw_syscalls:sys_enter: NR 1 (1, ... ^^ Correct comm 203a18 syscall_trace_enter_phase2+0xfe2001a8 ([kernel.kallsyms]) 203aa5 syscall_trace_enter+0xfe200055 ([kernel.kallsyms]) 203caa do_syscall_64+0xfe2000fa ([kernel.kallsyms]) b18d83 return_from_SYSCALL_64+0xfe200000 ([kernel.kallsyms]) d8e50 __GI___libc_write+0xffff01d9639f4010 (/tmp/oxygen_root-w00229757/lib64/libc-2.18.so) ^^^^^ Correct unwind This option doesn't aim to solve this problem completely. If a process terminates before SIGUSR2, we still lost its COMM and MMAP events. For example, we can't unwind correctly from the final perf.data we get from the previous example, because when perf collects the final output file (when we press C-c), 'dd' has been terminated so its '/proc/<pid>/mmap' becomes empty. However, this is a cheaper choice. To completely solve this problem we need to continously output non-sample events. To satisify the requirement of daemonization, we need to merge them periodically. It is possible but requires much more code and cycles. Automatically select --tail-synthesize when --overwrite is provided. Signed-off-by: Wang Nan <wangnan0@huawei.com> Cc: He Kuang <hekuang@huawei.com> Cc: Jiri Olsa <jolsa@kernel.org> Cc: Masami Hiramatsu <mhiramat@kernel.org> Cc: Namhyung Kim <namhyung@kernel.org> Cc: Nilay Vaish <nilayvaish@gmail.com> Cc: Zefan Li <lizefan@huawei.com> Cc: pi3orama@163.com Link: http://lkml.kernel.org/r/1468485287-33422-16-git-send-email-wangnan0@huawei.com Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Diffstat (limited to 'tools/perf/perf.h')
-rw-r--r--tools/perf/perf.h1
1 files changed, 1 insertions, 0 deletions
diff --git a/tools/perf/perf.h b/tools/perf/perf.h
index 608b42bdb1b6..a7e0f1497244 100644
--- a/tools/perf/perf.h
+++ b/tools/perf/perf.h
@@ -59,6 +59,7 @@ struct record_opts {
bool record_switch_events;
bool all_kernel;
bool all_user;
+ bool tail_synthesize;
bool overwrite;
unsigned int freq;
unsigned int mmap_pages;