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Date: Wed, 15 May 2024 21:19:48 -0700
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Subject: [PATCH v1 3/3] perf top: Allow filters on events
From: Ian Rogers <irogers@google.com>
To: Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@redhat.com>, 
	Arnaldo Carvalho de Melo <acme@kernel.org>, Namhyung Kim <namhyung@kernel.org>, 
	Mark Rutland <mark.rutland@arm.com>, 
	Alexander Shishkin <alexander.shishkin@linux.intel.com>, Jiri Olsa <jolsa@kernel.org>, 
	Ian Rogers <irogers@google.com>, Adrian Hunter <adrian.hunter@intel.com>, 
	Kan Liang <kan.liang@linux.intel.com>, Changbin Du <changbin.du@huawei.com>, 
	John Fastabend <john.fastabend@gmail.com>, Andrii Nakryiko <andrii@kernel.org>, 
	linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, 
	bpf@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"

Allow filters to be added to perf top events. One use is to workaround
issues with:
```
$ perf top --uid="$(id -u)"
```
which tries to scan /proc find processes belonging to the uid and can
fail in such a pid terminates between the scan and the
perf_event_open reporting:
```
Error:
The sys_perf_event_open() syscall returned with 3 (No such process) for event (cycles:P).
/bin/dmesg | grep -i perf may provide additional information.
```
A similar filter:
```
$ perf top -e cycles:P --filter "uid == $(id -u)"
```
doesn't fail this way.

Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/perf/Documentation/perf-top.txt | 4 ++++
 tools/perf/builtin-top.c              | 9 +++++++++
 2 files changed, 13 insertions(+)

diff --git a/tools/perf/Documentation/perf-top.txt b/tools/perf/Documentation/perf-top.txt
index a754875fa5bb..667e5102075e 100644
--- a/tools/perf/Documentation/perf-top.txt
+++ b/tools/perf/Documentation/perf-top.txt
@@ -43,6 +43,10 @@ Default is to monitor all CPUS.
 	encoding with the layout of the event control registers as described
 	by entries in /sys/bus/event_source/devices/cpu/format/*.
 
+--filter=<filter>::
+	Event filter.  This option should follow an event selector (-e). For
+	syntax see linkperf:perf-record[1].
+
 -E <entries>::
 --entries=<entries>::
 	Display this many functions.
diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c
index 1d6aef51c122..e8cbbf10d361 100644
--- a/tools/perf/builtin-top.c
+++ b/tools/perf/builtin-top.c
@@ -1055,6 +1055,13 @@ static int perf_top__start_counters(struct perf_top *top)
 		}
 	}
 
+	if (evlist__apply_filters(evlist, &counter)) {
+		pr_err("failed to set filter \"%s\" on event %s with %d (%s)\n",
+			counter->filter ?: "BPF", evsel__name(counter), errno,
+			str_error_r(errno, msg, sizeof(msg)));
+		goto out_err;
+	}
+
 	if (evlist__mmap(evlist, opts->mmap_pages) < 0) {
 		ui__error("Failed to mmap with %d (%s)\n",
 			    errno, str_error_r(errno, msg, sizeof(msg)));
@@ -1462,6 +1469,8 @@ int cmd_top(int argc, const char **argv)
 	OPT_CALLBACK('e', "event", &parse_events_option_args, "event",
 		     "event selector. use 'perf list' to list available events",
 		     parse_events_option),
+	OPT_CALLBACK(0, "filter", &top.evlist, "filter",
+		     "event filter", parse_filter),
 	OPT_U64('c', "count", &opts->user_interval, "event period to sample"),
 	OPT_STRING('p', "pid", &target->pid, "pid",
 		    "profile events on existing process id"),
-- 
2.45.0.rc1.225.g2a3ae87e7f-goog