linux-kernel - [PATCH 2/2] perf script: flush output stream after events in verbose mode

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Date:   Sun, 21 Oct 2018 21:14:24 +0200
From:   Milian Wolff <milian.wolff@...b.com>
To:     acme@...nel.org, jolsa@...nel.org
Cc:     Linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        Milian Wolff <milian.wolff@...b.com>
Subject: [PATCH 2/2] 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>
Cc: Arnaldo Carvalho de Melo <acme@...nel.org>
---
 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;
-- 
2.19.1