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Subject[PATCH v4] perf record: Add support for limit perf output file size
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The patch adds a new option to limit the output file size, then based
on it, we can create a wrapper of the perf command that uses the option
to avoid exhausting the disk space by the unconscious user.

In order to make the perf.data parsable, we just limit the sample data
size, since the perf.data consists of many headers and sample data and
other data, the actual size of the recorded file will bigger than the
setting value.

Testing it:

# ./perf record -a -g --max-size=10M
Couldn't synthesize bpf events.
WARNING: The perf data has already reached the limit, stop recording!
[ perf record: Woken up 30 times to write data ]
[ perf record: Captured and wrote 10.233 MB perf.data (175650 samples) ]
Terminated

# ls -lh perf.data
-rw------- 1 root root 11M Jul 17 14:01 perf.data

# ./perf record -a -g --max-size=10K
WARNING: The perf data has already reached the limit, stop recording!
Couldn't synthesize bpf events.
[ perf record: Woken up 0 times to write data ]
[ perf record: Captured and wrote 1.824 MB perf.data (67 samples) ]
Terminated

# ls -lh perf.data
-rw------- 1 root root 1.9M Jul 17 14:05 perf.data

Signed-off-by: Jiwei Sun <jiwei.sun@windriver.com>
---
v4 changes:
- Just show one WARNING message after reached the limit.

v3 changes:
- add a test result
- add the new option to tools/perf/Documentation/perf-record.txt

v2 changes:
- make patch based on latest Arnaldo's perf/core,
- display warning message when reached the limit.
---
tools/perf/Documentation/perf-record.txt | 4 +++
tools/perf/builtin-record.c | 42 ++++++++++++++++++++++++
2 files changed, 46 insertions(+)

diff --git a/tools/perf/Documentation/perf-record.txt b/tools/perf/Documentation/perf-record.txt
index c6f9f31b6039..f1c6113fbc82 100644
--- a/tools/perf/Documentation/perf-record.txt
+++ b/tools/perf/Documentation/perf-record.txt
@@ -571,6 +571,10 @@ config terms. For example: 'cycles/overwrite/' and 'instructions/no-overwrite/'.

Implies --tail-synthesize.

+--max-size=<size>::
+Limit the sample data max size, <size> is expected to be a number with
+appended unit character - B/K/M/G
+
SEE ALSO
--------
linkperf:perf-stat[1], linkperf:perf-list[1]
diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index 48600c90cc7e..30904d2a3407 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -91,6 +91,7 @@ struct record {
struct switch_output switch_output;
unsigned long long samples;
cpu_set_t affinity_mask;
+ unsigned long output_max_size; /* = 0: unlimited */
};

static volatile int auxtrace_record__snapshot_started;
@@ -120,6 +121,12 @@ static bool switch_output_time(struct record *rec)
trigger_is_ready(&switch_output_trigger);
}

+static bool record__output_max_size_exceeded(struct record *rec)
+{
+ return rec->output_max_size &&
+ (rec->bytes_written >= rec->output_max_size);
+}
+
static int record__write(struct record *rec, struct mmap *map __maybe_unused,
void *bf, size_t size)
{
@@ -132,6 +139,12 @@ static int record__write(struct record *rec, struct mmap *map __maybe_unused,

rec->bytes_written += size;

+ if (record__output_max_size_exceeded(rec)) {
+ WARN_ONCE(1, "WARNING: The perf data has already reached "
+ "the limit, stop recording!\n");
+ raise(SIGTERM);
+ }
+
if (switch_output_size(rec))
trigger_hit(&switch_output_trigger);

@@ -1936,6 +1949,33 @@ static int record__parse_affinity(const struct option *opt, const char *str, int
return 0;
}

+static int parse_output_max_size(const struct option *opt,
+ const char *str, int unset)
+{
+ unsigned long *s = (unsigned long *)opt->value;
+ static struct parse_tag tags_size[] = {
+ { .tag = 'B', .mult = 1 },
+ { .tag = 'K', .mult = 1 << 10 },
+ { .tag = 'M', .mult = 1 << 20 },
+ { .tag = 'G', .mult = 1 << 30 },
+ { .tag = 0 },
+ };
+ unsigned long val;
+
+ if (unset) {
+ *s = 0;
+ return 0;
+ }
+
+ val = parse_tag_value(str, tags_size);
+ if (val != (unsigned long) -1) {
+ *s = val;
+ return 0;
+ }
+
+ return -1;
+}
+
static int record__parse_mmap_pages(const struct option *opt,
const char *str,
int unset __maybe_unused)
@@ -2262,6 +2302,8 @@ static struct option __record_options[] = {
"n", "Compressed records using specified level (default: 1 - fastest compression, 22 - greatest compression)",
record__parse_comp_level),
#endif
+ OPT_CALLBACK(0, "max-size", &record.output_max_size,
+ "size", "Limit the maximum size of the output file", parse_output_max_size),
OPT_END()
};

--
2.20.1
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