linux-kernel - [tip:perf/urgent] perf script: Flush output stream after events in verbose mode

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Date:   Fri, 26 Oct 2018 00:35:00 -0700
From:   tip-bot for Milian Wolff <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     acme@...hat.com, tglx@...utronix.de, milian.wolff@...b.com,
        mingo@...nel.org, hpa@...or.com, linux-kernel@...r.kernel.org,
        jolsa@...nel.org
Subject: [tip:perf/urgent] perf script: Flush output stream after events in
 verbose mode

Commit-ID:  7ee40678af935fb489b0c6cf0f75808175214cd7
Gitweb:     https://git.kernel.org/tip/7ee40678af935fb489b0c6cf0f75808175214cd7
Author:     Milian Wolff <milian.wolff@...b.com>
AuthorDate: Sun, 21 Oct 2018 21:14:24 +0200
Committer:  Arnaldo Carvalho de Melo <acme@...hat.com>
CommitDate: Mon, 22 Oct 2018 14:27:11 -0300

perf script: Flush output stream after events in verbose mode

When the perf script output is written to a terminal stream, the normal
output of `perf script` would get buffered, but its debug output would
be written directly. This made it quite hard to figure out where a given
debug output is coming from.

We can improve on this by flushing the output buffer after processing an
event. To see the value, compare the following output for a `perf script
-v` run:

Before this patch:
```
unwind: reg 16, val 7faf7dfdc000
unwind: reg 7, val 7ffc80811e30
unwind: find_proc_info dso /usr/lib/ld-2.28.so
unwind: reg 6, val 0
unwind: _start:ip = 0x7faf7dfdc000 (0x2000)
unwind: reg 16, val 7faf7dfdc000
unwind: reg 7, val 7ffc80811e30
unwind: find_proc_info dso /usr/lib/ld-2.28.so
unwind: reg 6, val 0
unwind: _start:ip = 0x7faf7dfdc000 (0x2000)
unwind: reg 16, val 7faf7dfdc000
unwind: reg 7, val 7ffc80811e30
unwind: find_proc_info dso /usr/lib/ld-2.28.so
unwind: reg 6, val 0
unwind: _start:ip = 0x7faf7dfdc000 (0x2000)
unwind: reg 16, val 7faf7dfdc000
unwind: reg 7, val 7ffc80811e30
... lots and lots of verbose debug output
cpp-inlining 24617 90229.122036534:          1 cycles:uppp:
            7faf7dfdc000 _start+0x0 (/usr/lib/ld-2.28.so)

cpp-inlining 24617 90229.122043974:          1 cycles:uppp:
            7faf7dfdc000 _start+0x0 (/usr/lib/ld-2.28.so)
...
```

After this patch:
```
...
unwind: reg 16, val 7faf7dfdc000
unwind: reg 7, val 7ffc80811e30
unwind: find_proc_info dso /usr/lib/ld-2.28.so
unwind: reg 6, val 0
unwind: _start:ip = 0x7faf7dfdc000 (0x2000)
cpp-inlining 24617 90229.122036534:          1 cycles:uppp:
            7faf7dfdc000 _start+0x0 (/usr/lib/ld-2.28.so)

unwind: reg 16, val 7faf7dfdc000
unwind: reg 7, val 7ffc80811e30
unwind: find_proc_info dso /usr/lib/ld-2.28.so
unwind: reg 6, val 0
unwind: _start:ip = 0x7faf7dfdc000 (0x2000)
cpp-inlining 24617 90229.122043974:          1 cycles:uppp:
            7faf7dfdc000 _start+0x0 (/usr/lib/ld-2.28.so)
...
```

This new output format makes it much easier to use perf script output
for debugging purposes, e.g. to investigate broken dwarf unwinding.

Signed-off-by: Milian Wolff <milian.wolff@...b.com>
Acked-by: Jiri Olsa <jolsa@...nel.org>
Link: http://lkml.kernel.org/r/20181021191424.16183-2-milian.wolff@kdab.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
---
 tools/perf/builtin-script.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/tools/perf/builtin-script.c b/tools/perf/builtin-script.c
index bd468b90801b..ca09b7d2adb7 100644
--- a/tools/perf/builtin-script.c
+++ b/tools/perf/builtin-script.c
@@ -1737,6 +1737,9 @@ static void process_event(struct perf_script *script,
 
 	if (PRINT_FIELD(METRIC))
 		perf_sample__fprint_metric(script, thread, evsel, sample, fp);
+
+	if (verbose)
+		fflush(fp);
 }
 
 static struct scripting_ops	*scripting_ops;