linux-kernel - [PATCH RFC 3/9] timekeeping: add new debugfs file to count multigrain timestamps

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Message-Id: <20231018-mgtime-v1-3-4a7a97b1f482@kernel.org>
Date:   Wed, 18 Oct 2023 13:41:10 -0400
From:   Jeff Layton <jlayton@...nel.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <brauner@...nel.org>,
        John Stultz <jstultz@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Stephen Boyd <sboyd@...nel.org>,
        Chandan Babu R <chandan.babu@...cle.com>,
        "Darrick J. Wong" <djwong@...nel.org>,
        Dave Chinner <david@...morbit.com>,
        Theodore Ts'o <tytso@....edu>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Chris Mason <clm@...com>, Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>,
        Hugh Dickins <hughd@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Amir Goldstein <amir73il@...il.com>, Jan Kara <jack@...e.de>,
        David Howells <dhowells@...hat.com>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-xfs@...r.kernel.org, linux-ext4@...r.kernel.org,
        linux-btrfs@...r.kernel.org, linux-mm@...ck.org,
        linux-nfs@...r.kernel.org, Jeff Layton <jlayton@...nel.org>
Subject: [PATCH RFC 3/9] timekeeping: add new debugfs file to count
 multigrain timestamps

Add two percpu counters for tracking multigrain timestamps -- one for
coarse-grained timestamps and one for fine-grained ones. Add a new
debugfs file for summing them and outputting the result.

Signed-off-by: Jeff Layton <jlayton@...nel.org>
---
 kernel/time/timekeeping.c | 37 +++++++++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 7c20c98b1ea8..c843838cb643 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -24,6 +24,8 @@
 #include <linux/compiler.h>
 #include <linux/audit.h>
 #include <linux/random.h>
+#include <linux/seq_file.h>
+#include <linux/debugfs.h>
 
 #include "tick-internal.h"
 #include "ntp_internal.h"
@@ -59,6 +61,9 @@ static struct {
 
 static struct timekeeper shadow_timekeeper;
 
+struct percpu_counter mg_fine_ts;
+struct percpu_counter mg_coarse_ts;
+
 /* flag for if timekeeping is suspended */
 int __read_mostly timekeeping_suspended;
 
@@ -2326,6 +2331,7 @@ void ktime_get_mg_fine_ts64(struct timespec64 *ts)
 
 	ts->tv_nsec = 0;
 	timespec64_add_ns(ts, nsecs);
+	percpu_counter_inc(&mg_fine_ts);
 }
 
 /**
@@ -2361,6 +2367,7 @@ void ktime_get_mg_coarse_ts64(struct timespec64 *ts)
 		ts->tv_nsec = 0;
 		timespec64_add_ns(ts, nsec);
 	}
+	percpu_counter_inc(&mg_coarse_ts);
 }
 
 /*
@@ -2581,3 +2588,33 @@ void hardpps(const struct timespec64 *phase_ts, const struct timespec64 *raw_ts)
 }
 EXPORT_SYMBOL(hardpps);
 #endif /* CONFIG_NTP_PPS */
+
+static int fgts_show(struct seq_file *s, void *p)
+{
+	u64 fine = percpu_counter_sum(&mg_fine_ts);
+	u64 coarse = percpu_counter_sum(&mg_coarse_ts);
+
+	seq_printf(s, "%llu %llu\n", fine, coarse);
+	return 0;
+}
+
+DEFINE_SHOW_ATTRIBUTE(fgts);
+
+static int __init tk_debugfs_init(void)
+{
+	int ret = percpu_counter_init(&mg_fine_ts, 0, GFP_KERNEL);
+
+	if (ret)
+		return ret;
+
+	ret = percpu_counter_init(&mg_coarse_ts, 0, GFP_KERNEL);
+	if (ret) {
+		percpu_counter_destroy(&mg_fine_ts);
+		return ret;
+	}
+
+	debugfs_create_file("multigrain_timestamps", S_IFREG | S_IRUGO,
+				NULL, NULL, &fgts_fops);
+	return 0;
+}
+late_initcall(tk_debugfs_init);

-- 
2.41.0