time_stats: report information in json format

Export json versions of time statistics information.  Given the tabular
nature of the numbers exposed, this will make it a lot easier for higher
(than C) level languages (e.g. python) to import information without
needing to write yet another clumsy string parser.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

2 files changed, 89 insertions, 0 deletions

diff --git a/include/linux/time_stats.h b/include/linux/time_stats.h
index 047c4d99fb56..29fece3f9e71 100644
--- a/include/linux/time_stats.h
+++ b/include/linux/time_stats.h
@@ -148,6 +148,8 @@ void time_stats_reset(struct time_stats *);
 struct seq_buf;
 void time_stats_to_seq_buf(struct seq_buf *, struct time_stats *,
 		const char *epoch_name, unsigned int flags);
+void time_stats_to_json(struct seq_buf *, struct time_stats *,
+		const char *epoch_name, unsigned int flags);
 
 void time_stats_exit(struct time_stats *);
 void time_stats_init(struct time_stats *);
diff --git a/lib/time_stats.c b/lib/time_stats.c
index 261b1151797d..3539c0d4aa4b 100644
--- a/lib/time_stats.c
+++ b/lib/time_stats.c
@@ -281,6 +281,93 @@ void time_stats_to_seq_buf(struct seq_buf *out, struct time_stats *stats,
 }
 EXPORT_SYMBOL_GPL(time_stats_to_seq_buf);
 
+void time_stats_to_json(struct seq_buf *out, struct time_stats *stats,
+		const char *epoch_name, unsigned int flags)
+{
+	struct quantiles *quantiles = time_stats_to_quantiles(stats);
+	s64 f_mean = 0, d_mean = 0;
+	u64 f_stddev = 0, d_stddev = 0;
+
+	if (stats->buffer) {
+		int cpu;
+
+		spin_lock_irq(&stats->lock);
+		for_each_possible_cpu(cpu)
+			__time_stats_clear_buffer(stats, per_cpu_ptr(stats->buffer, cpu));
+		spin_unlock_irq(&stats->lock);
+	}
+
+	if (stats->freq_stats.n) {
+		/* avoid divide by zero */
+		f_mean = mean_and_variance_get_mean(stats->freq_stats);
+		f_stddev = mean_and_variance_get_stddev(stats->freq_stats);
+		d_mean = mean_and_variance_get_mean(stats->duration_stats);
+		d_stddev = mean_and_variance_get_stddev(stats->duration_stats);
+	} else if (flags & TIME_STATS_PRINT_NO_ZEROES) {
+		/* unless we didn't want zeroes anyway */
+		return;
+	}
+
+	seq_buf_printf(out, "{\n");
+	seq_buf_printf(out, "  \"epoch\":       \"%s\",\n", epoch_name);
+	seq_buf_printf(out, "  \"count\":       %llu,\n", stats->duration_stats.n);
+
+	seq_buf_printf(out, "  \"duration_ns\": {\n");
+	seq_buf_printf(out, "    \"min\":       %llu,\n", stats->min_duration);
+	seq_buf_printf(out, "    \"max\":       %llu,\n", stats->max_duration);
+	seq_buf_printf(out, "    \"total\":     %llu,\n", stats->total_duration);
+	seq_buf_printf(out, "    \"mean\":      %llu,\n", d_mean);
+	seq_buf_printf(out, "    \"stddev\":    %llu\n", d_stddev);
+	seq_buf_printf(out, "  },\n");
+
+	d_mean = mean_and_variance_weighted_get_mean(stats->duration_stats_weighted, TIME_STATS_MV_WEIGHT);
+	d_stddev = mean_and_variance_weighted_get_stddev(stats->duration_stats_weighted, TIME_STATS_MV_WEIGHT);
+
+	seq_buf_printf(out, "  \"duration_ewma_ns\": {\n");
+	seq_buf_printf(out, "    \"mean\":      %llu,\n", d_mean);
+	seq_buf_printf(out, "    \"stddev\":    %llu\n", d_stddev);
+	seq_buf_printf(out, "  },\n");
+
+	seq_buf_printf(out, "  \"between_ns\": {\n");
+	seq_buf_printf(out, "    \"min\":       %llu,\n", stats->min_freq);
+	seq_buf_printf(out, "    \"max\":       %llu,\n", stats->max_freq);
+	seq_buf_printf(out, "    \"mean\":      %llu,\n", f_mean);
+	seq_buf_printf(out, "    \"stddev\":    %llu\n", f_stddev);
+	seq_buf_printf(out, "  },\n");
+
+	f_mean = mean_and_variance_weighted_get_mean(stats->freq_stats_weighted, TIME_STATS_MV_WEIGHT);
+	f_stddev = mean_and_variance_weighted_get_stddev(stats->freq_stats_weighted, TIME_STATS_MV_WEIGHT);
+
+	seq_buf_printf(out, "  \"between_ewma_ns\": {\n");
+	seq_buf_printf(out, "    \"mean\":      %llu,\n", f_mean);
+	seq_buf_printf(out, "    \"stddev\":    %llu\n", f_stddev);
+
+	if (quantiles) {
+		u64 last_q = 0;
+
+		/* close between_ewma_ns but signal more items */
+		seq_buf_printf(out, "  },\n");
+
+		seq_buf_printf(out, "  \"quantiles_ns\": [\n");
+		eytzinger0_for_each(i, NR_QUANTILES) {
+			bool is_last = eytzinger0_next(i, NR_QUANTILES) == -1;
+
+			u64 q = max(quantiles->entries[i].m, last_q);
+			seq_buf_printf(out, "    %llu", q);
+			if (!is_last)
+				seq_buf_printf(out, ", ");
+			last_q = q;
+		}
+		seq_buf_printf(out, "  ]\n");
+	} else {
+		/* close between_ewma_ns without dumping further */
+		seq_buf_printf(out, "  }\n");
+	}
+
+	seq_buf_printf(out, "}\n");
+}
+EXPORT_SYMBOL_GPL(time_stats_to_json);
+
 void time_stats_exit(struct time_stats *stats)
 {
 	free_percpu(stats->buffer);