Add request size histograms (-r) to zpool iostat, minor man page fix

Add -r option to "zpool iostat" to print request size histograms for the leaf
ZIOs. This includes histograms of individual ZIOs ("ind") and aggregate ZIOs
("agg"). These stats can be useful for seeing how well the ZFS IO aggregator
is working.

$ zpool iostat -r
mypool        sync_read    sync_write    async_read    async_write      scrub
req_size      ind    agg    ind    agg    ind    agg    ind    agg    ind    agg
----------  -----  -----  -----  -----  -----  -----  -----  -----  -----  -----
512             0      0      0      0      0      0    530      0      0      0
1K              0      0    260      0      0      0    116    246      0      0
2K              0      0      0      0      0      0      0    431      0      0
4K              0      0      0      0      0      0      3    107      0      0
8K             15      0     35      0      0      0      0      6      0      0
16K             0      0      0      0      0      0      0     39      0      0
32K             0      0      0      0      0      0      0      0      0      0
64K            20      0     40      0      0      0      0      0      0      0
128K            0      0     20      0      0      0      0      0      0      0
256K            0      0      0      0      0      0      0      0      0      0
512K            0      0      0      0      0      0      0      0      0      0
1M              0      0      0      0      0      0      0      0      0      0
2M              0      0      0      0      0      0      0      0      0      0
4M              0      0      0      0      0      0    155     19      0      0
8M              0      0      0      0      0      0      0    811      0      0
16M             0      0      0      0      0      0      0     68      0      0
--------------------------------------------------------------------------------

Also rename the stray "-G" in the man page to be "-w" for latency histograms.

Signed-off-by: Tony Hutter <[email protected]>
Signed-off-by: Brian Behlendorf <[email protected]>
Signed-off-by: Tim Chase <[email protected]>
Closes #4659

1 files changed, 187 insertions, 89 deletions

diff --git a/cmd/zpool/zpool_main.c b/cmd/zpool/zpool_main.c
index 0603efdba..072404264 100644
--- a/cmd/zpool/zpool_main.c
+++ b/cmd/zpool/zpool_main.c
@@ -153,6 +153,7 @@ enum iostat_type {
 	IOS_LATENCY = 1,
 	IOS_QUEUES = 2,
 	IOS_L_HISTO = 3,
+	IOS_RQ_HISTO = 4,
 	IOS_COUNT,	/* always last element */
 };
 
@@ -161,6 +162,62 @@ enum iostat_type {
 #define	IOS_LATENCY_M	(1ULL << IOS_LATENCY)
 #define	IOS_QUEUES_M	(1ULL << IOS_QUEUES)
 #define	IOS_L_HISTO_M	(1ULL << IOS_L_HISTO)
+#define	IOS_RQ_HISTO_M	(1ULL << IOS_RQ_HISTO)
+
+/* Mask of all the histo bits */
+#define	IOS_ANYHISTO_M (IOS_L_HISTO_M | IOS_RQ_HISTO_M)
+
+/*
+ * Lookup table for iostat flags to nvlist names.  Basically a list
+ * of all the nvlists a flag requires.  Also specifies the order in
+ * which data gets printed in zpool iostat.
+ */
+static const char *vsx_type_to_nvlist[IOS_COUNT][11] = {
+	[IOS_L_HISTO] = {
+	    ZPOOL_CONFIG_VDEV_TOT_R_LAT_HISTO,
+	    ZPOOL_CONFIG_VDEV_TOT_W_LAT_HISTO,
+	    ZPOOL_CONFIG_VDEV_DISK_R_LAT_HISTO,
+	    ZPOOL_CONFIG_VDEV_DISK_W_LAT_HISTO,
+	    ZPOOL_CONFIG_VDEV_SYNC_R_LAT_HISTO,
+	    ZPOOL_CONFIG_VDEV_SYNC_W_LAT_HISTO,
+	    ZPOOL_CONFIG_VDEV_ASYNC_R_LAT_HISTO,
+	    ZPOOL_CONFIG_VDEV_ASYNC_W_LAT_HISTO,
+	    ZPOOL_CONFIG_VDEV_SCRUB_LAT_HISTO,
+	    NULL},
+	[IOS_LATENCY] = {
+	    ZPOOL_CONFIG_VDEV_TOT_R_LAT_HISTO,
+	    ZPOOL_CONFIG_VDEV_TOT_W_LAT_HISTO,
+	    ZPOOL_CONFIG_VDEV_DISK_R_LAT_HISTO,
+	    ZPOOL_CONFIG_VDEV_DISK_W_LAT_HISTO,
+	    NULL},
+	[IOS_QUEUES] = {
+	    ZPOOL_CONFIG_VDEV_SYNC_R_ACTIVE_QUEUE,
+	    ZPOOL_CONFIG_VDEV_SYNC_W_ACTIVE_QUEUE,
+	    ZPOOL_CONFIG_VDEV_ASYNC_R_ACTIVE_QUEUE,
+	    ZPOOL_CONFIG_VDEV_ASYNC_W_ACTIVE_QUEUE,
+	    ZPOOL_CONFIG_VDEV_SCRUB_ACTIVE_QUEUE,
+	    NULL},
+	[IOS_RQ_HISTO] = {
+	    ZPOOL_CONFIG_VDEV_SYNC_IND_R_HISTO,
+	    ZPOOL_CONFIG_VDEV_SYNC_AGG_R_HISTO,
+	    ZPOOL_CONFIG_VDEV_SYNC_IND_W_HISTO,
+	    ZPOOL_CONFIG_VDEV_SYNC_AGG_W_HISTO,
+	    ZPOOL_CONFIG_VDEV_ASYNC_IND_R_HISTO,
+	    ZPOOL_CONFIG_VDEV_ASYNC_AGG_R_HISTO,
+	    ZPOOL_CONFIG_VDEV_ASYNC_IND_W_HISTO,
+	    ZPOOL_CONFIG_VDEV_ASYNC_AGG_W_HISTO,
+	    ZPOOL_CONFIG_VDEV_IND_SCRUB_HISTO,
+	    ZPOOL_CONFIG_VDEV_AGG_SCRUB_HISTO,
+	    NULL},
+};
+
+
+/*
+ * Given a cb->cb_flags with a histogram bit set, return the iostat_type.
+ * Right now, only one histo bit is ever set at one time, so we can
+ * just do a highbit64(a)
+ */
+#define	IOS_HISTO_IDX(a)	(highbit64(a & IOS_ANYHISTO_M) - 1)
 
 typedef struct zpool_command {
 	const char	*name;
@@ -255,7 +312,8 @@ get_usage(zpool_help_t idx) {
 		    "[-R root] [-F [-n]]\n"
 		    "\t    <pool | id> [newpool]\n"));
 	case HELP_IOSTAT:
-		return (gettext("\tiostat [-T d | u] [-ghHLpPvy] [[-lq]|-w]\n"
+		return (gettext("\tiostat [-T d | u] [-ghHLpPvy] "
+		    "[[-lq]|[-r|-w]]\n"
 		    "\t    [[pool ...]|[pool vdev ...]|[vdev ...]] "
 		    "[interval [count]]\n"));
 	case HELP_LABELCLEAR:
@@ -2531,6 +2589,9 @@ static const name_and_columns_t iostat_top_labels[][IOSTAT_MAX_LABELS] =
 	    {NULL}},
 	[IOS_L_HISTO] = {{"total_wait", 2}, {"disk_wait", 2},
 	    {"sync_queue", 2}, {"async_queue", 2}, {NULL}},
+	[IOS_RQ_HISTO] = {{"sync_read", 2}, {"sync_write", 2},
+	    {"async_read", 2}, {"async_write", 2}, {"scrub", 2}, {NULL}},
+
 };
 
 /* Shorthand - if "columns" field not set, default to 1 column */
@@ -2544,6 +2605,13 @@ static const name_and_columns_t iostat_bottom_labels[][IOSTAT_MAX_LABELS] =
 	    {"activ"}, {"pend"}, {"activ"}, {"pend"}, {"activ"}, {NULL}},
 	[IOS_L_HISTO] = {{"read"}, {"write"}, {"read"}, {"write"}, {"read"},
 	    {"write"}, {"read"}, {"write"}, {"scrub"}, {NULL}},
+	[IOS_RQ_HISTO] = {{"ind"}, {"agg"}, {"ind"}, {"agg"}, {"ind"}, {"agg"},
+	    {"ind"}, {"agg"}, {"ind"}, {"agg"}, {NULL}},
+};
+
+static const char *histo_to_title[] = {
+	[IOS_L_HISTO] = "latency",
+	[IOS_RQ_HISTO] = "req_size",
 };
 
 /*
@@ -2563,6 +2631,25 @@ label_array_len(const name_and_columns_t *labels)
 }
 
 /*
+ * Return the number of strings in a null-terminated string array.
+ * For example:
+ *
+ *     const char foo[] = {"bar", "baz", NULL}
+ *
+ * returns 2
+ */
+static uint64_t
+str_array_len(const char *array[])
+{
+	uint64_t i = 0;
+	while (array[i])
+		i++;
+
+	return (i);
+}
+
+
+/*
  * Return a default column width for default/latency/queue columns. This does
  * not include histograms, which have their columns autosized.
  */
@@ -2673,14 +2760,22 @@ print_iostat_dashes(iostat_cbdata_t *cb, unsigned int force_column_width,
 	uint64_t f;
 	int idx;
 	const name_and_columns_t *labels;
+	const char *title;
+
+
+	if (cb->cb_flags & IOS_ANYHISTO_M) {
+		title = histo_to_title[IOS_HISTO_IDX(cb->cb_flags)];
+	} else if (cb->cb_vdev_names_count) {
+		title = "vdev";
+	} else  {
+		title = "pool";
+	}
+
+	namewidth = MAX(MAX(strlen(title), cb->cb_namewidth),
+	    name ? strlen(name) : 0);
 
-	if (cb->cb_flags & IOS_L_HISTO_M)
-		namewidth = MAX(cb->cb_namewidth, strlen("latency"));
-	else
-		namewidth = cb->cb_namewidth;
 
 	if (name) {
-		namewidth = MAX(cb->cb_namewidth, strlen(name));
 		printf("%-*s", namewidth, name);
 	} else {
 		for (i = 0; i < namewidth; i++)
@@ -2727,22 +2822,28 @@ print_iostat_header_impl(iostat_cbdata_t *cb, unsigned int force_column_width,
     const char *histo_vdev_name)
 {
 	unsigned int namewidth;
-	uint64_t flags = cb->cb_flags;
+	const char *title;
 
-	if (flags & IOS_L_HISTO_M)
-		namewidth = MAX(cb->cb_namewidth, strlen("latency"));
-	else
-		namewidth = cb->cb_namewidth;
+	if (cb->cb_flags & IOS_ANYHISTO_M) {
+		title = histo_to_title[IOS_HISTO_IDX(cb->cb_flags)];
+	} else if (cb->cb_vdev_names_count) {
+		title = "vdev";
+	} else  {
+		title = "pool";
+	}
 
-	if (flags & IOS_L_HISTO_M)
+	namewidth = MAX(MAX(strlen(title), cb->cb_namewidth),
+	    histo_vdev_name ? strlen(histo_vdev_name) : 0);
+
+	if (histo_vdev_name)
 		printf("%-*s", namewidth, histo_vdev_name);
 	else
 		printf("%*s", namewidth, "");
 
+
 	print_iostat_labels(cb, force_column_width, iostat_top_labels);
 
-	printf("%-*s", namewidth, flags & IOS_L_HISTO_M ? "latency" :
-	    cb->cb_vdev_names_count ? "vdev" : "pool");
+	printf("%-*s", namewidth, title);
 
 	print_iostat_labels(cb, force_column_width, iostat_bottom_labels);
 
@@ -2918,6 +3019,7 @@ print_iostat_histo(struct stat_array *nva, unsigned int len,
 	uint64_t val;
 	enum zfs_nicenum_format format;
 	unsigned int buckets;
+	unsigned int start_bucket;
 
 	if (cb->cb_literal)
 		format = ZFS_NICENUM_RAW;
@@ -2927,12 +3029,25 @@ print_iostat_histo(struct stat_array *nva, unsigned int len,
 	/* All these histos are the same size, so just use nva[0].count */
 	buckets = nva[0].count;
 
-	for (j = 0; j < buckets; j++) {
-		/* Ending range of this bucket */
-		val = (1UL << (j + 1)) - 1;
+	if (cb->cb_flags & IOS_RQ_HISTO_M) {
+		/* Start at 512 - req size should never be lower than this */
+		start_bucket = 9;
+	} else {
+		start_bucket = 0;
+	}
 
+	for (j = start_bucket; j < buckets; j++) {
 		/* Print histogram bucket label */
-		zfs_nicetime(val, buf, sizeof (buf));
+		if (cb->cb_flags & IOS_L_HISTO_M) {
+			/* Ending range of this bucket */
+			val = (1UL << (j + 1)) - 1;
+			zfs_nicetime(val, buf, sizeof (buf));
+		} else {
+			/* Request size (starting range of bucket) */
+			val = (1UL << j);
+			zfs_nicenum(val, buf, sizeof (buf));
+		}
+
 		if (cb->cb_scripted)
 			printf("%llu", (u_longlong_t) val);
 		else
@@ -2962,30 +3077,29 @@ print_iostat_histos(iostat_cbdata_t *cb, nvlist_t *oldnv,
 	unsigned int column_width;
 	unsigned int namewidth;
 	unsigned int entire_width;
-
-	const char *names[] = {
-		ZPOOL_CONFIG_VDEV_TOT_R_LAT_HISTO,
-		ZPOOL_CONFIG_VDEV_TOT_W_LAT_HISTO,
-		ZPOOL_CONFIG_VDEV_DISK_R_LAT_HISTO,
-		ZPOOL_CONFIG_VDEV_DISK_W_LAT_HISTO,
-		ZPOOL_CONFIG_VDEV_SYNC_R_LAT_HISTO,
-		ZPOOL_CONFIG_VDEV_SYNC_W_LAT_HISTO,
-		ZPOOL_CONFIG_VDEV_ASYNC_R_LAT_HISTO,
-		ZPOOL_CONFIG_VDEV_ASYNC_W_LAT_HISTO,
-		ZPOOL_CONFIG_VDEV_SCRUB_LAT_HISTO,
-	};
+	enum iostat_type type;
 	struct stat_array *nva;
-	nva = calc_and_alloc_stats_ex(names, ARRAY_SIZE(names), oldnv, newnv);
+	const char **names;
+	unsigned int names_len;
+
+	/* What type of histo are we? */
+	type = IOS_HISTO_IDX(cb->cb_flags);
+
+	/* Get NULL-terminated array of nvlist names for our histo */
+	names = vsx_type_to_nvlist[type];
+	names_len = str_array_len(names); /* num of names */
+
+	nva = calc_and_alloc_stats_ex(names, names_len, oldnv, newnv);
 
 	if (cb->cb_literal) {
 		column_width = MAX(5,
-		    (unsigned int) log10(stat_histo_max(nva,
-		    ARRAY_SIZE(names))) + 1);
+		    (unsigned int) log10(stat_histo_max(nva, names_len)) + 1);
 	} else {
 		column_width = 5;
 	}
 
-	namewidth = MAX(cb->cb_namewidth, strlen("latency"));
+	namewidth = MAX(cb->cb_namewidth,
+	    strlen(histo_to_title[IOS_HISTO_IDX(cb->cb_flags)]));
 
 	/*
 	 * Calculate the entire line width of what we're printing.  The
@@ -2998,17 +3112,17 @@ print_iostat_histos(iostat_cbdata_t *cb, nvlist_t *oldnv,
 	/*	|__________|  <--- entire_width		*/
 	/*						*/
 	entire_width = namewidth + (column_width + 2) *
-	    label_array_len(iostat_bottom_labels[IOS_L_HISTO]);
+	    label_array_len(iostat_bottom_labels[type]);
 
 	if (cb->cb_scripted)
 		printf("%s\n", name);
 	else
 		print_iostat_header_impl(cb, column_width, name);
 
-	print_iostat_histo(nva, ARRAY_SIZE(names), cb, column_width,
+	print_iostat_histo(nva, names_len, cb, column_width,
 	    namewidth, scale);
 
-	free_calc_stats(nva, ARRAY_SIZE(names));
+	free_calc_stats(nva, names_len);
 	if (!cb->cb_scripted)
 		print_solid_separator(entire_width);
 }
@@ -3219,7 +3333,7 @@ print_vdev_stats(zpool_handle_t *zhp, const char *name, nvlist_t *oldnv,
 	 * Print the vdev name unless it's is a histogram.  Histograms
 	 * display the vdev name in the header itself.
 	 */
-	if (!(cb->cb_flags & IOS_L_HISTO_M)) {
+	if (!(cb->cb_flags & IOS_ANYHISTO_M)) {
 		if (cb->cb_scripted) {
 			printf("%s", name);
 		} else {
@@ -3234,7 +3348,7 @@ print_vdev_stats(zpool_handle_t *zhp, const char *name, nvlist_t *oldnv,
 
 	/* Calculate our scaling factor */
 	tdelta = newvs->vs_timestamp - oldvs->vs_timestamp;
-	if ((oldvs->vs_timestamp == 0) && (cb->cb_flags & IOS_L_HISTO_M)) {
+	if ((oldvs->vs_timestamp == 0) && (cb->cb_flags & IOS_ANYHISTO_M)) {
 		/*
 		 * If we specify printing histograms with no time interval, then
 		 * print the histogram numbers over the entire lifetime of the
@@ -3256,12 +3370,12 @@ print_vdev_stats(zpool_handle_t *zhp, const char *name, nvlist_t *oldnv,
 		print_iostat_latency(cb, oldnv, newnv, scale);
 	if (cb->cb_flags & IOS_QUEUES_M)
 		print_iostat_queues(cb, oldnv, newnv, scale);
-	if (cb->cb_flags & IOS_L_HISTO_M) {
+	if (cb->cb_flags & IOS_ANYHISTO_M) {
 		printf("\n");
 		print_iostat_histos(cb, oldnv, newnv, scale, name);
 	}
 
-	if (!(cb->cb_flags & IOS_L_HISTO_M))
+	if (!(cb->cb_flags & IOS_ANYHISTO_M))
 		printf("\n");
 
 	free(calcvs);
@@ -3303,7 +3417,7 @@ children:
 	 */
 
 	if (num_logs(newnv) > 0) {
-		if ((!(cb->cb_flags & IOS_L_HISTO_M)) && !cb->cb_scripted &&
+		if ((!(cb->cb_flags & IOS_ANYHISTO_M)) && !cb->cb_scripted &&
 		    !cb->cb_vdev_names) {
 			print_iostat_dashes(cb, 0, "logs");
 		}
@@ -3337,7 +3451,7 @@ children:
 		return (ret);
 
 	if (children > 0) {
-		if ((!(cb->cb_flags & IOS_L_HISTO_M)) && !cb->cb_scripted &&
+		if ((!(cb->cb_flags & IOS_ANYHISTO_M)) && !cb->cb_scripted &&
 		    !cb->cb_vdev_names) {
 			print_iostat_dashes(cb, 0, "cache");
 		}
@@ -3399,9 +3513,10 @@ print_iostat(zpool_handle_t *zhp, void *data)
 
 	ret = print_vdev_stats(zhp, zpool_get_name(zhp), oldnvroot, newnvroot,
 									cb, 0);
-	if ((ret != 0) && !(cb->cb_flags & IOS_L_HISTO_M) && !cb->cb_scripted &&
-	    cb->cb_verbose && !cb->cb_vdev_names_count)
-				print_iostat_separator(cb);
+	if ((ret != 0) && !(cb->cb_flags & IOS_ANYHISTO_M) &&
+	    !cb->cb_scripted && cb->cb_verbose && !cb->cb_vdev_names_count) {
+		print_iostat_separator(cb);
+	}
 
 	return (ret);
 }
@@ -3553,37 +3668,6 @@ get_stat_flags_cb(zpool_handle_t *zhp, void *data)
 	uint64_t flags = 0;
 	int i, j;
 
-	/*
-	 * Lookup table for extended iostat flags to nvlist names.
-	 * Basically a list of all the nvpairs a flag requires.
-	 */
-	static const char *vsx_type_to_nvlist[IOS_COUNT][10] = {
-		[IOS_L_HISTO] = {
-		    ZPOOL_CONFIG_VDEV_TOT_R_LAT_HISTO,
-		    ZPOOL_CONFIG_VDEV_TOT_W_LAT_HISTO,
-		    ZPOOL_CONFIG_VDEV_DISK_R_LAT_HISTO,
-		    ZPOOL_CONFIG_VDEV_DISK_W_LAT_HISTO,
-		    ZPOOL_CONFIG_VDEV_SYNC_R_LAT_HISTO,
-		    ZPOOL_CONFIG_VDEV_SYNC_W_LAT_HISTO,
-		    ZPOOL_CONFIG_VDEV_ASYNC_R_LAT_HISTO,
-		    ZPOOL_CONFIG_VDEV_ASYNC_W_LAT_HISTO,
-		    ZPOOL_CONFIG_VDEV_SCRUB_LAT_HISTO,
-		    NULL},
-		[IOS_LATENCY] = {
-		    ZPOOL_CONFIG_VDEV_TOT_R_LAT_HISTO,
-		    ZPOOL_CONFIG_VDEV_TOT_W_LAT_HISTO,
-		    ZPOOL_CONFIG_VDEV_DISK_R_LAT_HISTO,
-		    ZPOOL_CONFIG_VDEV_DISK_W_LAT_HISTO,
-		    NULL},
-		[IOS_QUEUES] = {
-		    ZPOOL_CONFIG_VDEV_SYNC_R_ACTIVE_QUEUE,
-		    ZPOOL_CONFIG_VDEV_SYNC_W_ACTIVE_QUEUE,
-		    ZPOOL_CONFIG_VDEV_ASYNC_R_ACTIVE_QUEUE,
-		    ZPOOL_CONFIG_VDEV_ASYNC_W_ACTIVE_QUEUE,
-		    ZPOOL_CONFIG_VDEV_SCRUB_ACTIVE_QUEUE,
-		    NULL}
-	};
-
 	config = zpool_get_config(zhp, NULL);
 	verify(nvlist_lookup_nvlist(config, ZPOOL_CONFIG_VDEV_TREE,
 	    &nvroot) == 0);
@@ -3818,7 +3902,7 @@ fsleep(float sec) {
 
 
 /*
- * zpool iostat [-ghHLpPvy] [[-lq]-w] [-n name] [-T d|u]
+ * zpool iostat [-ghHLpPvy] [[-lq]|[-r|-w]] [-n name] [-T d|u]
  *		[[ pool ...]|[pool vdev ...]|[vdev ...]]
  *		[interval [count]]
  *
@@ -3832,7 +3916,8 @@ fsleep(float sec) {
  *		by a single tab.
  *	-l	Display average latency
  *	-q	Display queue depths
- *	-w	Display histograms
+ *	-w	Display latency histograms
+ *	-r	Display request size histogram
  *	-T	Display a timestamp in date(1) or Unix format
  *
  * This command can be tricky because we want to be able to deal with pool
@@ -3851,7 +3936,7 @@ zpool_do_iostat(int argc, char **argv)
 	unsigned long count = 0;
 	zpool_list_t *list;
 	boolean_t verbose = B_FALSE;
-	boolean_t latency = B_FALSE, histo = B_FALSE;
+	boolean_t latency = B_FALSE, l_histo = B_FALSE, rq_histo = B_FALSE;
 	boolean_t queues = B_FALSE, parsable = B_FALSE, scripted = B_FALSE;
 	boolean_t omit_since_boot = B_FALSE;
 	boolean_t guid = B_FALSE;
@@ -3861,12 +3946,12 @@ zpool_do_iostat(int argc, char **argv)
 
 	/* Used for printing error message */
 	const char flag_to_arg[] = {[IOS_LATENCY] = 'l', [IOS_QUEUES] = 'q',
-	    [IOS_L_HISTO] = 'w'};
+	    [IOS_L_HISTO] = 'w', [IOS_RQ_HISTO] = 'r'};
 
 	uint64_t unsupported_flags;
 
 	/* check options */
-	while ((c = getopt(argc, argv, "gLPT:vyhplqwH")) != -1) {
+	while ((c = getopt(argc, argv, "gLPT:vyhplqrwH")) != -1) {
 		switch (c) {
 		case 'g':
 			guid = B_TRUE;
@@ -3896,7 +3981,10 @@ zpool_do_iostat(int argc, char **argv)
 			scripted = B_TRUE;
 			break;
 		case 'w':
-			histo = B_TRUE;
+			l_histo = B_TRUE;
+			break;
+		case 'r':
+			rq_histo = B_TRUE;
 			break;
 		case 'y':
 			omit_since_boot = B_TRUE;
@@ -3997,10 +4085,18 @@ zpool_do_iostat(int argc, char **argv)
 		return (1);
 	}
 
-	if (histo && (queues || latency)) {
+	if ((l_histo || rq_histo) && (queues || latency)) {
+		pool_list_free(list);
+		(void) fprintf(stderr,
+		    gettext("[-r|-w] isn't allowed with [-q|-l]\n"));
+		usage(B_FALSE);
+		return (1);
+	}
+
+	if (l_histo && rq_histo) {
 		pool_list_free(list);
 		(void) fprintf(stderr,
-		    gettext("-w isn't allowed with [-q|-l]\n"));
+		    gettext("Only one of [-r|-w] can be passed at a time\n"));
 		usage(B_FALSE);
 		return (1);
 	}
@@ -4010,13 +4106,15 @@ zpool_do_iostat(int argc, char **argv)
 	 */
 	cb.cb_list = list;
 
-	if (histo) {
+	if (l_histo) {
 		/*
 		 * Histograms tables look out of place when you try to display
 		 * them with the other stats, so make a rule that you can only
 		 * print histograms by themselves.
 		 */
 		cb.cb_flags = IOS_L_HISTO_M;
+	} else if (rq_histo) {
+		cb.cb_flags = IOS_RQ_HISTO_M;
 	} else {
 		cb.cb_flags = IOS_DEFAULT_M;
 		if (latency)
@@ -4088,7 +4186,7 @@ zpool_do_iostat(int argc, char **argv)
 			 */
 			if (((++cb.cb_iteration == 1 && !skip) ||
 			    (skip != verbose)) &&
-			    (!(cb.cb_flags & IOS_L_HISTO_M)) &&
+			    (!(cb.cb_flags & IOS_ANYHISTO_M)) &&
 			    !cb.cb_scripted)
 				print_iostat_header(&cb);
 
@@ -4108,8 +4206,8 @@ zpool_do_iostat(int argc, char **argv)
 			 * we also want an ending separator.
 			 */
 			if (((npools > 1 && !verbose &&
-			    !(cb.cb_flags & IOS_L_HISTO_M)) ||
-			    (!(cb.cb_flags & IOS_L_HISTO_M) &&
+			    !(cb.cb_flags & IOS_ANYHISTO_M)) ||
+			    (!(cb.cb_flags & IOS_ANYHISTO_M) &&
 			    cb.cb_vdev_names_count)) &&
 			    !cb.cb_scripted) {
 				print_iostat_separator(&cb);