perf top: Switch default mode to overwrite mode (ebebbf08) · Commits · 戴 / test

perf_top__mmap_read() has a severe performance issue in the Knights Landing/Mill platform, when monitoring heavy load systems. It costs several minutes to finish, which is unacceptable. Currently, 'perf top' uses the non overwrite mode. For non overwrite mode, it tries to read everything in the ringbuffer and doesn't pause it. Once there are lots of samples delivered persistently, the processing time could be very long. Also, the latest samples could be lost when the ringbuffer is full. For overwrite mode, it takes a snapshot for the system by pausing the ringbuffer, which could significantly reduce the processing time. Also, the overwrite mode always keep the latest samples. Considering the real time requirement for 'perf top', the overwrite mode is more suitable for it. Actually, 'perf top' was overwrite mode. It is changed to non overwrite mode since commit ("perf top: Switch to non overwrite mode"). It's better to change it back to overwrite mode by default. For the kernel which doesn't support overwrite mode, it will fall back to non overwrite mode. There would be some records lost in overwrite mode because of pausing the ringbuffer. It has little impact for the accuracy of the snapshot and can be tolerated. For overwrite mode, unconditionally wait 100 ms before each snapshot. It also reduces the overhead caused by pausing ringbuffer, especially on light load system. Signed-off-by:

Kan Liang <kan.liang@intel.com> Acked-by:

Jiri Olsa <jolsa@kernel.org> Tested-by:

Arnaldo Carvalho de Melo <acme@redhat.com> Cc: Andi Kleen <ak@linux.intel.com> Cc: Jin Yao <yao.jin@linux.intel.com> Cc: Namhyung Kim <namhyung@kernel.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Wang Nan <wangnan0@huawei.com> Link: http://lkml.kernel.org/r/1516310792-208685-17-git-send-email-kan.liang@intel.com Signed-off-by:

Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-top.c

+25 −9

Original line number	Diff line number	Diff line
		@@ -809,15 +809,23 @@ static void perf_event__process_sample(struct perf_tool *tool,

		static void perf_top__mmap_read_idx(struct perf_top *top, int idx)
		{
		struct record_opts *opts = &top->record_opts;
		struct perf_evlist *evlist = top->evlist;
		struct perf_sample sample;
		struct perf_evsel *evsel;
		struct perf_mmap *md;
		struct perf_session *session = top->session;
		union perf_event *event;
		struct machine *machine;
		u64 end, start;
		int ret;

		while ((event = perf_evlist__mmap_read(top->evlist, idx)) != NULL) {
		ret = perf_evlist__parse_sample(top->evlist, event, &sample);
		md = opts->overwrite ? &evlist->overwrite_mmap[idx] : &evlist->mmap[idx];
		if (perf_mmap__read_init(md, opts->overwrite, &start, &end) < 0)
		return;

		while ((event = perf_mmap__read_event(md, opts->overwrite, &start, end)) != NULL) {
		ret = perf_evlist__parse_sample(evlist, event, &sample);
		if (ret) {
		pr_err("Can't parse sample, err = %d\n", ret);
		goto next_event;
		@@ -871,16 +879,28 @@ static void perf_top__mmap_read_idx(struct perf_top *top, int idx)
		} else
		++session->evlist->stats.nr_unknown_events;
		next_event:
		perf_evlist__mmap_consume(top->evlist, idx);
		perf_mmap__consume(md, opts->overwrite);
		}

		perf_mmap__read_done(md);
		}

		static void perf_top__mmap_read(struct perf_top *top)
		{
		bool overwrite = top->record_opts.overwrite;
		struct perf_evlist *evlist = top->evlist;
		int i;

		if (overwrite)
		perf_evlist__toggle_bkw_mmap(evlist, BKW_MMAP_DATA_PENDING);

		for (i = 0; i < top->evlist->nr_mmaps; i++)
		perf_top__mmap_read_idx(top, i);

		if (overwrite) {
		perf_evlist__toggle_bkw_mmap(evlist, BKW_MMAP_EMPTY);
		perf_evlist__toggle_bkw_mmap(evlist, BKW_MMAP_RUNNING);
		}
		}

		/*
		@@ -979,11 +999,6 @@ static int perf_top__start_counters(struct perf_top *top)
		goto out_err;
		}

		if (opts->overwrite) {
		ui__error("not support overwrite mode yet\n");
		goto out_err;
		}

		perf_evlist__config(evlist, opts, &callchain_param);

		evlist__for_each_entry(evlist, counter) {
		@@ -1144,7 +1159,7 @@ static int __cmd_top(struct perf_top *top)

		perf_top__mmap_read(top);

		if (hits == top->samples)
		if (opts->overwrite \|\| (hits == top->samples))
		ret = perf_evlist__poll(top->evlist, 100);

		if (resize) {
		@@ -1238,6 +1253,7 @@ int cmd_top(int argc, const char **argv)
		.uses_mmap = true,
		},
		.proc_map_timeout = 500,
		.overwrite = 1,
		},
		.max_stack = sysctl_perf_event_max_stack,
		.sym_pcnt_filter = 5,

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