bcachefs: Better congestion visibilty in sysfs

/sys/fs/bcachefs/<uuid>/dev-n/congested now prints more info on how we
calculate device congestion.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

3 files changed, 60 insertions, 16 deletions

diff --git a/fs/bcachefs/io_read.c b/fs/bcachefs/io_read.c
index 2f458fc88f03..f24c1c3e8f19 100644
--- a/fs/bcachefs/io_read.c
+++ b/fs/bcachefs/io_read.c
@@ -45,38 +45,73 @@ MODULE_PARM_DESC(poison_extents_on_checksum_error,
 
 #ifndef CONFIG_BCACHEFS_NO_LATENCY_ACCT
 
+static inline u32 bch2_dev_congested_read(struct bch_dev *ca, u64 now)
+{
+	s64 congested = atomic_read(&ca->congested);
+	u64 last = READ_ONCE(ca->congested_last);
+	if (time_after64(now, last))
+		congested -= (now - last) >> 12;
+
+	return clamp(congested, 0LL, CONGESTED_MAX);
+}
+
 static bool bch2_target_congested(struct bch_fs *c, u16 target)
 {
 	const struct bch_devs_mask *devs;
 	unsigned d, nr = 0, total = 0;
-	u64 now = local_clock(), last;
-	s64 congested;
-	struct bch_dev *ca;
-
-	if (!target)
-		return false;
+	u64 now = local_clock();
 
 	guard(rcu)();
 	devs = bch2_target_to_mask(c, target) ?:
 		&c->rw_devs[BCH_DATA_user];
 
 	for_each_set_bit(d, devs->d, BCH_SB_MEMBERS_MAX) {
-		ca = rcu_dereference(c->devs[d]);
+		struct bch_dev *ca = rcu_dereference(c->devs[d]);
 		if (!ca)
 			continue;
 
-		congested = atomic_read(&ca->congested);
-		last = READ_ONCE(ca->congested_last);
-		if (time_after64(now, last))
-			congested -= (now - last) >> 12;
-
-		total += max(congested, 0LL);
+		total += bch2_dev_congested_read(ca, now);
 		nr++;
 	}
 
 	return get_random_u32_below(nr * CONGESTED_MAX) < total;
 }
 
+void bch2_dev_congested_to_text(struct printbuf *out, struct bch_dev *ca)
+{
+	printbuf_tabstop_push(out, 32);
+
+	prt_printf(out, "current:\t%u%%\n",
+		   bch2_dev_congested_read(ca, local_clock()) *
+		   100 / CONGESTED_MAX);
+
+	prt_printf(out, "raw:\t%i/%u\n", atomic_read(&ca->congested), CONGESTED_MAX);
+
+	prt_printf(out, "last io over threshold:\t");
+	bch2_pr_time_units(out, local_clock() - ca->congested_last);
+	prt_newline(out);
+
+	prt_printf(out, "read latency threshold:\t");
+	bch2_pr_time_units(out,
+			   ca->io_latency[READ].quantiles.entries[QUANTILE_IDX(1)].m << 2);
+	prt_newline(out);
+
+	prt_printf(out, "median read latency:\t");
+	bch2_pr_time_units(out,
+			   ca->io_latency[READ].quantiles.entries[QUANTILE_IDX(7)].m);
+	prt_newline(out);
+
+	prt_printf(out, "write latency threshold:\t");
+	bch2_pr_time_units(out,
+			   ca->io_latency[WRITE].quantiles.entries[QUANTILE_IDX(1)].m << 3);
+	prt_newline(out);
+
+	prt_printf(out, "median write latency:\t");
+	bch2_pr_time_units(out,
+			   ca->io_latency[WRITE].quantiles.entries[QUANTILE_IDX(7)].m);
+	prt_newline(out);
+}
+
 #else
 
 static bool bch2_target_congested(struct bch_fs *c, u16 target)
diff --git a/fs/bcachefs/io_read.h b/fs/bcachefs/io_read.h
index 1afd19402682..8fef4e47f16d 100644
--- a/fs/bcachefs/io_read.h
+++ b/fs/bcachefs/io_read.h
@@ -7,6 +7,10 @@
 #include "extents_types.h"
 #include "reflink.h"
 
+#ifndef CONFIG_BCACHEFS_NO_LATENCY_ACCT
+void bch2_dev_congested_to_text(struct printbuf *, struct bch_dev *);
+#endif
+
 struct bch_read_bio {
 	struct bch_fs		*c;
 	u64			start_time;
diff --git a/fs/bcachefs/sysfs.c b/fs/bcachefs/sysfs.c
index 05848375cea2..ac8d03d3c835 100644
--- a/fs/bcachefs/sysfs.c
+++ b/fs/bcachefs/sysfs.c
@@ -170,7 +170,9 @@ read_attribute(io_latency_read);
 read_attribute(io_latency_write);
 read_attribute(io_latency_stats_read);
 read_attribute(io_latency_stats_write);
+#ifndef CONFIG_BCACHEFS_NO_LATENCY_ACCT
 read_attribute(congested);
+#endif
 
 read_attribute(btree_write_stats);
 
@@ -830,9 +832,10 @@ SHOW(bch2_dev)
 	if (attr == &sysfs_io_latency_stats_write)
 		bch2_time_stats_to_text(out, &ca->io_latency[WRITE].stats);
 
-	sysfs_printf(congested,			"%u%%",
-		     clamp(atomic_read(&ca->congested), 0, CONGESTED_MAX)
-		     * 100 / CONGESTED_MAX);
+#ifndef CONFIG_BCACHEFS_NO_LATENCY_ACCT
+	if (attr == &sysfs_congested)
+		bch2_dev_congested_to_text(out, ca);
+#endif
 
 	if (attr == &sysfs_alloc_debug)
 		bch2_dev_alloc_debug_to_text(out, ca);
@@ -900,7 +903,9 @@ struct attribute *bch2_dev_files[] = {
 	&sysfs_io_latency_write,
 	&sysfs_io_latency_stats_read,
 	&sysfs_io_latency_stats_write,
+#ifndef CONFIG_BCACHEFS_NO_LATENCY_ACCT
 	&sysfs_congested,
+#endif
 
 	/* debug: */
 	&sysfs_alloc_debug,