linux-kernel - [PATCH] perf record: Disallow -c and -F option at the same time

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Message-Id: <20210402094020.28164-1-namhyung@kernel.org>
Date:   Fri,  2 Apr 2021 18:40:20 +0900
From:   Namhyung Kim <namhyung@...nel.org>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...hat.com>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Ian Rogers <irogers@...gle.com>,
        Alexey Alexandrov <aalexand@...gle.com>
Subject: [PATCH] perf record: Disallow -c and -F option at the same time

It's confusing which one is effective when the both options are given.
The current code happens to use -c in this case but users might not be
aware of it.  We can change it to complain about that instead of
relying on the implicit priority.

Before:
  $ perf record -c 111111 -F 99 true
  [ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 0.031 MB perf.data (8 samples) ]

  $ perf evlist -F
  cycles: sample_period=111111

After:
  $ perf record -c 111111 -F 99 true
  cannot set frequency and period at the same time

So this change can break existing usages, but I think it's rare to
have both options and it'd be better changing them.

Suggested-by: Alexey Alexandrov <aalexand@...gle.com>
Signed-off-by: Namhyung Kim <namhyung@...nel.org>
---
 tools/perf/util/record.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/record.c b/tools/perf/util/record.c
index f99852d54b14..43e5b563dee8 100644
--- a/tools/perf/util/record.c
+++ b/tools/perf/util/record.c
@@ -157,9 +157,15 @@ static int get_max_rate(unsigned int *rate)
 static int record_opts__config_freq(struct record_opts *opts)
 {
 	bool user_freq = opts->user_freq != UINT_MAX;
+	bool user_interval = opts->user_interval != ULLONG_MAX;
 	unsigned int max_rate;
 
-	if (opts->user_interval != ULLONG_MAX)
+	if (user_interval && user_freq) {
+		pr_err("cannot set frequency and period at the same time\n");
+		return -1;
+	}
+
+	if (user_interval)
 		opts->default_interval = opts->user_interval;
 	if (user_freq)
 		opts->freq = opts->user_freq;
-- 
2.31.0.208.g409f899ff0-goog