Report duration and error in mmp_history entries

After an MMP write completes, update the relevant mmp_history entry
with the time between submission and completion, and the error
status of the write.

[faaland1@toss3a zfs]$ cat /proc/spl/kstat/zfs/pool/multihost
39 0 0x01 100 8800 69147946270893 72723903122926
id       txg     timestamp  error  duration   mmp_delay    vdev_guid
10607    1166    1518985089 0      138301     637785455    4882...
10608    1166    1518985089 0      136154     635407747    1151...
10609    1166    1518985089 0      803618560  633048078    9740...
10610    1166    1518985090 0      144826     633048078    4882...
10611    1166    1518985090 0      164527     666187671    1151...

Where duration = gethrtime_in_done_fn - gethrtime_at_submission, and
error = zio->io_error.

Reviewed-by: Giuseppe Di Natale <dinatale2@llnl.gov>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Olaf Faaland <faaland1@llnl.gov>
Closes openzfs#7190

include/sys/mmp.h

@@ -42,6 +42,7 @@ typedef struct mmp_thread {
 	uint64_t	mmp_delay;	/* decaying avg ns between MMP writes */
 	uberblock_t	mmp_ub;		/* last ub written by sync */
 	zio_t		*mmp_zio_root;	/* root of mmp write zios */
+	uint64_t	mmp_kstat_id;	/* unique id for next MMP write kstat */
 } mmp_thread_t;
 
 

include/sys/spa.h

@@ -759,8 +759,10 @@ extern txg_stat_t *spa_txg_history_init_io(spa_t *, uint64_t,
     struct dsl_pool *);
 extern void spa_txg_history_fini_io(spa_t *, txg_stat_t *);
 extern void spa_tx_assign_add_nsecs(spa_t *spa, uint64_t nsecs);
+extern int spa_mmp_history_set(spa_t *spa, uint64_t mmp_kstat_id, int io_error,
+    hrtime_t duration);
 extern void spa_mmp_history_add(uint64_t txg, uint64_t timestamp,
-    uint64_t mmp_delay, vdev_t *vd, int label);
+    uint64_t mmp_delay, vdev_t *vd, int label, uint64_t mmp_kstat_id);
 
 /* Pool configuration locks */
 extern int spa_config_tryenter(spa_t *spa, int locks, void *tag, krw_t rw);

include/sys/vdev_impl.h

@@ -238,6 +238,7 @@ struct vdev {
 	vdev_aux_t	vdev_label_aux;	/* on-disk aux state		*/
 	uint64_t	vdev_leaf_zap;
 	hrtime_t	vdev_mmp_pending; /* 0 if write finished	*/
+	uint64_t	vdev_mmp_kstat_id;	/* to find kstat entry */
 
 	/*
 	 * For DTrace to work in userland (libzpool) context, these fields must

module/zfs/mmp.c

@@ -135,6 +135,7 @@ mmp_init(spa_t *spa)
 	mutex_init(&mmp->mmp_thread_lock, NULL, MUTEX_DEFAULT, NULL);
 	cv_init(&mmp->mmp_thread_cv, NULL, CV_DEFAULT, NULL);
 	mutex_init(&mmp->mmp_io_lock, NULL, MUTEX_DEFAULT, NULL);
+	mmp->mmp_kstat_id = 1;
 }
 
 void
@@ -244,7 +245,8 @@ mmp_write_done(zio_t *zio)
 	mmp_thread_t *mts = zio->io_private;
 
 	mutex_enter(&mts->mmp_io_lock);
-	vd->vdev_mmp_pending = 0;
+	uint64_t mmp_kstat_id = vd->vdev_mmp_kstat_id;
+	hrtime_t mmp_write_duration = gethrtime() - vd->vdev_mmp_pending;
 
 	if (zio->io_error)
 		goto unlock;
@@ -278,9 +280,15 @@ mmp_write_done(zio_t *zio)
 	mts->mmp_last_write = gethrtime();
 
 unlock:
+	vd->vdev_mmp_pending = 0;
+	vd->vdev_mmp_kstat_id = 0;
+
 	mutex_exit(&mts->mmp_io_lock);
 	spa_config_exit(spa, SCL_STATE, mmp_tag);
 
+	spa_mmp_history_set(spa, mmp_kstat_id, zio->io_error,
+	    mmp_write_duration);
+
 	abd_free(zio->io_abd);
 }
 
@@ -333,6 +341,7 @@ mmp_write_uberblock(spa_t *spa)
 	ub->ub_mmp_magic = MMP_MAGIC;
 	ub->ub_mmp_delay = mmp->mmp_delay;
 	vd->vdev_mmp_pending = gethrtime();
+	vd->vdev_mmp_kstat_id = mmp->mmp_kstat_id++;
 
 	zio_t *zio  = zio_null(mmp->mmp_zio_root, spa, NULL, NULL, NULL, flags);
 	abd_t *ub_abd = abd_alloc_for_io(VDEV_UBERBLOCK_SIZE(vd), B_TRUE);
@@ -350,7 +359,7 @@ mmp_write_uberblock(spa_t *spa)
 	    flags | ZIO_FLAG_DONT_PROPAGATE);
 
 	spa_mmp_history_add(ub->ub_txg, ub->ub_timestamp, ub->ub_mmp_delay, vd,
-	    label);
+	    label, vd->vdev_mmp_kstat_id);
 
 	zio_nowait(zio);
 }

module/zfs/spa_stats.c

@@ -718,21 +718,24 @@ spa_io_history_destroy(spa_t *spa)
  */
 
 typedef struct spa_mmp_history {
+	uint64_t	mmp_kstat_id;	/* unique # for updates */
 	uint64_t	txg;		/* txg of last sync */
 	uint64_t	timestamp;	/* UTC time of of last sync */
 	uint64_t	mmp_delay;	/* nanosec since last MMP write */
 	uint64_t	vdev_guid;	/* unique ID of leaf vdev */
 	char		*vdev_path;
 	uint64_t	vdev_label;	/* vdev label */
+	int		io_error;	/* error status of MMP write */
+	hrtime_t	duration;	/* time from submission to completion */
 	list_node_t	smh_link;
 } spa_mmp_history_t;
 
 static int
 spa_mmp_history_headers(char *buf, size_t size)
 {
-	(void) snprintf(buf, size, "%-10s %-10s %-12s %-24s %-10s %s\n",
-	    "txg", "timestamp", "mmp_delay", "vdev_guid", "vdev_label",
-	    "vdev_path");
+	(void) snprintf(buf, size, "%-10s %-10s %-10s %-6s %-10s %-12s %-24s "
+	    "%-10s %s\n", "id", "txg", "timestamp", "error", "duration",
+	    "mmp_delay", "vdev_guid", "vdev_label", "vdev_path");
 	return (0);
 }
 
@@ -741,11 +744,12 @@ spa_mmp_history_data(char *buf, size_t size, void *data)
 {
 	spa_mmp_history_t *smh = (spa_mmp_history_t *)data;
 
-	(void) snprintf(buf, size, "%-10llu %-10llu %-12llu %-24llu %-10llu "
-	    "%s\n",
-	    (u_longlong_t)smh->txg, (u_longlong_t)smh->timestamp,
-	    (u_longlong_t)smh->mmp_delay, (u_longlong_t)smh->vdev_guid,
-	    (u_longlong_t)smh->vdev_label,
+	(void) snprintf(buf, size, "%-10llu %-10llu %-10llu %-6lld %-10lld "
+	    "%-12llu %-24llu %-10llu %s\n",
+	    (u_longlong_t)smh->mmp_kstat_id, (u_longlong_t)smh->txg,
+	    (u_longlong_t)smh->timestamp, (longlong_t)smh->io_error,
+	    (longlong_t)smh->duration, (u_longlong_t)smh->mmp_delay,
+	    (u_longlong_t)smh->vdev_guid, (u_longlong_t)smh->vdev_label,
 	    (smh->vdev_path ? smh->vdev_path : "-"));
 
 	return (0);
@@ -861,11 +865,40 @@ spa_mmp_history_destroy(spa_t *spa)
 }
 
 /*
- * Add a new MMP update to historical record.
+ * Set MMP write duration and error status in existing record.
+ */
+int
+spa_mmp_history_set(spa_t *spa, uint64_t mmp_kstat_id, int io_error,
+    hrtime_t duration)
+{
+	spa_stats_history_t *ssh = &spa->spa_stats.mmp_history;
+	spa_mmp_history_t *smh;
+	int error = ENOENT;
+
+	if (zfs_multihost_history == 0 && ssh->size == 0)
+		return (0);
+
+	mutex_enter(&ssh->lock);
+	for (smh = list_head(&ssh->list); smh != NULL;
+	    smh = list_next(&ssh->list, smh)) {
+		if (smh->mmp_kstat_id == mmp_kstat_id) {
+			smh->io_error = io_error;
+			smh->duration = duration;
+			error = 0;
+			break;
+		}
+	}
+	mutex_exit(&ssh->lock);
+
+	return (error);
+}
+
+/*
+ * Add a new MMP write to historical record.
  */
 void
 spa_mmp_history_add(uint64_t txg, uint64_t timestamp, uint64_t mmp_delay,
-    vdev_t *vd, int label)
+    vdev_t *vd, int label, uint64_t mmp_kstat_id)
 {
 	spa_t *spa = vd->vdev_spa;
 	spa_stats_history_t *ssh = &spa->spa_stats.mmp_history;
@@ -882,6 +915,7 @@ spa_mmp_history_add(uint64_t txg, uint64_t timestamp, uint64_t mmp_delay,
 	if (vd->vdev_path)
 		smh->vdev_path = strdup(vd->vdev_path);
 	smh->vdev_label = label;
+	smh->mmp_kstat_id = mmp_kstat_id;
 
 	mutex_enter(&ssh->lock);