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Date: Fri, 23 Feb 2024 17:10:21 -0800
Subject: [PATCH 01/10] time_stats: report lifetime of the stats object
From: "Darrick J. Wong" <djwong@kernel.org>
To: akpm@linux-foundation.org, daniel@gluo.nz, kent.overstreet@linux.dev,
 djwong@kernel.org
Cc: linux-xfs@vger.kernel.org, linux-bcachefs@vger.kernel.org,
 linux-kernel@vger.kernel.org
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From: Darrick J. Wong <djwong@kernel.org>

Capture the initialization time of the time_stats object so that we can
report how long the counter has been observing data.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
---
 include/linux/time_stats.h |    2 ++
 lib/time_stats.c           |   10 ++++++++++
 2 files changed, 12 insertions(+)


diff --git a/include/linux/time_stats.h b/include/linux/time_stats.h
index caefa7aba65a0..eb1957cb77c0d 100644
--- a/include/linux/time_stats.h
+++ b/include/linux/time_stats.h
@@ -78,6 +78,8 @@ struct time_stats {
 	u64		last_event_start;
 	struct quantiles quantiles;
 
+	u64		start_time;
+
 	struct mean_and_variance	  duration_stats;
 	struct mean_and_variance_weighted duration_stats_weighted;
 	struct mean_and_variance	  freq_stats;
diff --git a/lib/time_stats.c b/lib/time_stats.c
index 081aeba88b535..8df4b55fc6337 100644
--- a/lib/time_stats.c
+++ b/lib/time_stats.c
@@ -158,10 +158,16 @@ static void seq_buf_time_units_aligned(struct seq_buf *out, u64 ns)
 	seq_buf_printf(out, "%8llu %s", div64_u64(ns, u->nsecs), u->name);
 }
 
+static inline u64 time_stats_lifetime(const struct time_stats *stats)
+{
+	return local_clock() - stats->start_time;
+}
+
 void time_stats_to_seq_buf(struct seq_buf *out, struct time_stats *stats)
 {
 	s64 f_mean = 0, d_mean = 0;
 	u64 f_stddev = 0, d_stddev = 0;
+	u64 lifetime = time_stats_lifetime(stats);
 
 	if (stats->buffer) {
 		int cpu;
@@ -183,6 +189,9 @@ void time_stats_to_seq_buf(struct seq_buf *out, struct time_stats *stats)
 	}
 
 	seq_buf_printf(out, "count: %llu\n", stats->duration_stats.n);
+	seq_buf_printf(out, "lifetime: ");
+	seq_buf_time_units_aligned(out, lifetime);
+	seq_buf_printf(out, "\n");
 
 	seq_buf_printf(out, "                       since mount        recent\n");
 
@@ -263,6 +272,7 @@ void time_stats_init(struct time_stats *stats)
 	stats->freq_stats_weighted.weight = 8;
 	stats->min_duration = U64_MAX;
 	stats->min_freq = U64_MAX;
+	stats->start_time = local_clock();
 	spin_lock_init(&stats->lock);
 }
 EXPORT_SYMBOL_GPL(time_stats_init);