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

7 files changed, 301 insertions, 106 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);
diff --git a/include/sys/fs/zfs.h b/include/sys/fs/zfs.h
index 65dba125c..9de50e9a2 100644
--- a/include/sys/fs/zfs.h
+++ b/include/sys/fs/zfs.h
@@ -558,7 +558,17 @@ typedef struct zpool_rewind_policy {
 #define	ZPOOL_CONFIG_VDEV_ASYNC_W_LAT_HISTO	"vdev_async_w_lat_histo"
 #define	ZPOOL_CONFIG_VDEV_SCRUB_LAT_HISTO	"vdev_scrub_histo"
 
-
+/* Request size histograms */
+#define	ZPOOL_CONFIG_VDEV_SYNC_IND_R_HISTO	"vdev_sync_ind_r_histo"
+#define	ZPOOL_CONFIG_VDEV_SYNC_IND_W_HISTO	"vdev_sync_ind_w_histo"
+#define	ZPOOL_CONFIG_VDEV_ASYNC_IND_R_HISTO	"vdev_async_ind_r_histo"
+#define	ZPOOL_CONFIG_VDEV_ASYNC_IND_W_HISTO	"vdev_async_ind_w_histo"
+#define	ZPOOL_CONFIG_VDEV_IND_SCRUB_HISTO	"vdev_ind_scrub_histo"
+#define	ZPOOL_CONFIG_VDEV_SYNC_AGG_R_HISTO	"vdev_sync_agg_r_histo"
+#define	ZPOOL_CONFIG_VDEV_SYNC_AGG_W_HISTO	"vdev_sync_agg_w_histo"
+#define	ZPOOL_CONFIG_VDEV_ASYNC_AGG_R_HISTO	"vdev_async_agg_r_histo"
+#define	ZPOOL_CONFIG_VDEV_ASYNC_AGG_W_HISTO	"vdev_async_agg_w_histo"
+#define	ZPOOL_CONFIG_VDEV_AGG_SCRUB_HISTO	"vdev_agg_scrub_histo"
 
 #define	ZPOOL_CONFIG_WHOLE_DISK		"whole_disk"
 #define	ZPOOL_CONFIG_ERRCOUNT		"error_count"
@@ -824,20 +834,33 @@ typedef struct vdev_stat_ex {
 	 * 2^37 nanoseconds = 134s. Timeouts will probably start kicking in
 	 * before this.
 	 */
-#define	VDEV_HISTO_BUCKETS 37
+#define	VDEV_L_HISTO_BUCKETS 37		/* Latency histo buckets */
+#define	VDEV_RQ_HISTO_BUCKETS 25	/* Request size histo buckets */
+
 
 	/* Amount of time in ZIO queue (ns) */
 	uint64_t vsx_queue_histo[ZIO_PRIORITY_NUM_QUEUEABLE]
-	    [VDEV_HISTO_BUCKETS];
+	    [VDEV_L_HISTO_BUCKETS];
 
 	/* Total ZIO latency (ns).  Includes queuing and disk access time */
-	uint64_t vsx_total_histo[ZIO_TYPES][VDEV_HISTO_BUCKETS];
+	uint64_t vsx_total_histo[ZIO_TYPES][VDEV_L_HISTO_BUCKETS];
 
 	/* Amount of time to read/write the disk (ns) */
-	uint64_t vsx_disk_histo[ZIO_TYPES][VDEV_HISTO_BUCKETS];
+	uint64_t vsx_disk_histo[ZIO_TYPES][VDEV_L_HISTO_BUCKETS];
+
+	/* "lookup the bucket for a value" histogram macros */
+#define	HISTO(val, buckets) (val != 0 ? MIN(highbit64(val) - 1, \
+	    buckets - 1) : 0)
+#define	L_HISTO(a) HISTO(a, VDEV_L_HISTO_BUCKETS)
+#define	RQ_HISTO(a) HISTO(a, VDEV_RQ_HISTO_BUCKETS)
+
+	/* Physical IO histogram */
+	uint64_t vsx_ind_histo[ZIO_PRIORITY_NUM_QUEUEABLE]
+	    [VDEV_RQ_HISTO_BUCKETS];
 
-	/* "lookup the bucket for a value" macro */
-#define	HISTO(a) (a != 0 ? MIN(highbit64(a) - 1, VDEV_HISTO_BUCKETS - 1) : 0)
+	/* Delegated (aggregated) physical IO histogram */
+	uint64_t vsx_agg_histo[ZIO_PRIORITY_NUM_QUEUEABLE]
+	    [VDEV_RQ_HISTO_BUCKETS];
 
 } vdev_stat_ex_t;
 
diff --git a/man/man8/zpool.8 b/man/man8/zpool.8
index eb35b74c0..80402c55e 100644
--- a/man/man8/zpool.8
+++ b/man/man8/zpool.8
@@ -95,7 +95,7 @@ zpool \- configures ZFS storage pools
 
 .LP
 .nf
-\fB\fBzpool iostat\fR [\fB-T\fR \fBd\fR | \fBu\fR] [\fB-ghHLpPvy\fR] [\fB-G\fR|[\fB-lq\fR]]
+\fB\fBzpool iostat\fR [\fB-T\fR \fBd\fR | \fBu\fR] [\fB-ghHLpPvy\fR] [\fB-lq\fR]|[\fB-r\fR|-\fBw\fR]]
      [[\fIpool\fR ...]|[\fIpool vdev\fR ...]|[\fIvdev\fR ...]] [\fIinterval\fR[\fIcount\fR]]\fR
 
 .fi
@@ -1510,7 +1510,7 @@ Scan using the default search path, the libblkid cache will not be consulted.  A
 .sp
 .ne 2
 .na
-\fB\fBzpool iostat\fR [\fB-T\fR \fBd\fR | \fBu\fR] [\fB-ghHLpPvy\fR] [\fB-w\fR|[\fB-lq\fR]] [[\fIpool\fR ...]|[\fIpool vdev\fR ...]|[\fIvdev\fR ...]] [\fIinterval\fR[\fIcount\fR]]\fR
+\fB\fBzpool iostat\fR [\fB-T\fR \fBd\fR | \fBu\fR] [\fB-ghHLpPvy\fR] [[\fB-lq\fR]|[\fB-r\fR|\fB-w\fR]] [[\fIpool\fR ...]|[\fIpool vdev\fR ...]|[\fIvdev\fR ...]] [\fIinterval\fR[\fIcount\fR]]\fR
 
 .ad
 .sp .6
@@ -1585,6 +1585,19 @@ Display full paths for vdevs instead of only the last component of the path.  Th
 .sp
 .ne 2
 .na
+\fB\fB-r\fR\fR
+.ad
+.RS 12n
+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.  Do not confuse these
+request size stats with the block layer requests; it's possible ZIOs can
+be broken up before being sent to the block device.
+.RE
+
+.sp
+.ne 2
+.na
 \fB\fB-v\fR\fR
 .ad
 .RS 12n
diff --git a/module/zfs/vdev.c b/module/zfs/vdev.c
index 137390173..607be3ce3 100644
--- a/module/zfs/vdev.c
+++ b/module/zfs/vdev.c
@@ -2784,21 +2784,30 @@ vdev_get_child_stat_ex(vdev_t *cvd, vdev_stat_ex_t *vsx, vdev_stat_ex_t *cvsx)
 {
 	int t, b;
 	for (t = 0; t < ZIO_TYPES; t++) {
-		for (b = 0; b < VDEV_HISTO_BUCKETS; b++) {
+		for (b = 0; b < ARRAY_SIZE(vsx->vsx_disk_histo[0]); b++)
 			vsx->vsx_disk_histo[t][b] += cvsx->vsx_disk_histo[t][b];
+
+		for (b = 0; b < ARRAY_SIZE(vsx->vsx_total_histo[0]); b++) {
 			vsx->vsx_total_histo[t][b] +=
 			    cvsx->vsx_total_histo[t][b];
 		}
 	}
 
 	for (t = 0; t < ZIO_PRIORITY_NUM_QUEUEABLE; t++) {
-		for (b = 0; b < VDEV_HISTO_BUCKETS; b++) {
+		for (b = 0; b < ARRAY_SIZE(vsx->vsx_queue_histo[0]); b++) {
 			vsx->vsx_queue_histo[t][b] +=
 			    cvsx->vsx_queue_histo[t][b];
 		}
 		vsx->vsx_active_queue[t] += cvsx->vsx_active_queue[t];
 		vsx->vsx_pend_queue[t] += cvsx->vsx_pend_queue[t];
+
+		for (b = 0; b < ARRAY_SIZE(vsx->vsx_ind_histo[0]); b++)
+			vsx->vsx_ind_histo[t][b] += cvsx->vsx_ind_histo[t][b];
+
+		for (b = 0; b < ARRAY_SIZE(vsx->vsx_agg_histo[0]); b++)
+			vsx->vsx_agg_histo[t][b] += cvsx->vsx_agg_histo[t][b];
 	}
+
 }
 
 /*
@@ -2974,13 +2983,21 @@ vdev_stat_update(zio_t *zio, uint64_t psize)
 			vs->vs_ops[type]++;
 			vs->vs_bytes[type] += psize;
 
+			if (flags & ZIO_FLAG_DELEGATED) {
+				vsx->vsx_agg_histo[zio->io_priority]
+				    [RQ_HISTO(zio->io_size)]++;
+			} else {
+				vsx->vsx_ind_histo[zio->io_priority]
+				    [RQ_HISTO(zio->io_size)]++;
+			}
+
 			if (zio->io_delta && zio->io_delay) {
 				vsx->vsx_queue_histo[zio->io_priority]
-				    [HISTO(zio->io_delta - zio->io_delay)]++;
+				    [L_HISTO(zio->io_delta - zio->io_delay)]++;
 				vsx->vsx_disk_histo[type]
-				    [HISTO(zio->io_delay)]++;
+				    [L_HISTO(zio->io_delay)]++;
 				vsx->vsx_total_histo[type]
-				    [HISTO(zio->io_delta)]++;
+				    [L_HISTO(zio->io_delta)]++;
 			}
 		}
 
diff --git a/module/zfs/vdev_label.c b/module/zfs/vdev_label.c
index 1400aee7b..59bce1370 100644
--- a/module/zfs/vdev_label.c
+++ b/module/zfs/vdev_label.c
@@ -302,6 +302,47 @@ vdev_config_generate_stats(vdev_t *vd, nvlist_t *nv)
 	    vsx->vsx_queue_histo[ZIO_PRIORITY_SCRUB],
 	    ARRAY_SIZE(vsx->vsx_queue_histo[ZIO_PRIORITY_SCRUB]));
 
+	/* Request sizes */
+	fnvlist_add_uint64_array(nvx, ZPOOL_CONFIG_VDEV_SYNC_IND_R_HISTO,
+	    vsx->vsx_ind_histo[ZIO_PRIORITY_SYNC_READ],
+	    ARRAY_SIZE(vsx->vsx_ind_histo[ZIO_PRIORITY_SYNC_READ]));
+
+	fnvlist_add_uint64_array(nvx, ZPOOL_CONFIG_VDEV_SYNC_IND_W_HISTO,
+	    vsx->vsx_ind_histo[ZIO_PRIORITY_SYNC_WRITE],
+	    ARRAY_SIZE(vsx->vsx_ind_histo[ZIO_PRIORITY_SYNC_WRITE]));
+
+	fnvlist_add_uint64_array(nvx, ZPOOL_CONFIG_VDEV_ASYNC_IND_R_HISTO,
+	    vsx->vsx_ind_histo[ZIO_PRIORITY_ASYNC_READ],
+	    ARRAY_SIZE(vsx->vsx_ind_histo[ZIO_PRIORITY_ASYNC_READ]));
+
+	fnvlist_add_uint64_array(nvx, ZPOOL_CONFIG_VDEV_ASYNC_IND_W_HISTO,
+	    vsx->vsx_ind_histo[ZIO_PRIORITY_ASYNC_WRITE],
+	    ARRAY_SIZE(vsx->vsx_ind_histo[ZIO_PRIORITY_ASYNC_WRITE]));
+
+	fnvlist_add_uint64_array(nvx, ZPOOL_CONFIG_VDEV_IND_SCRUB_HISTO,
+	    vsx->vsx_ind_histo[ZIO_PRIORITY_SCRUB],
+	    ARRAY_SIZE(vsx->vsx_ind_histo[ZIO_PRIORITY_SCRUB]));
+
+	fnvlist_add_uint64_array(nvx, ZPOOL_CONFIG_VDEV_SYNC_AGG_R_HISTO,
+	    vsx->vsx_agg_histo[ZIO_PRIORITY_SYNC_READ],
+	    ARRAY_SIZE(vsx->vsx_agg_histo[ZIO_PRIORITY_SYNC_READ]));
+
+	fnvlist_add_uint64_array(nvx, ZPOOL_CONFIG_VDEV_SYNC_AGG_W_HISTO,
+	    vsx->vsx_agg_histo[ZIO_PRIORITY_SYNC_WRITE],
+	    ARRAY_SIZE(vsx->vsx_agg_histo[ZIO_PRIORITY_SYNC_WRITE]));
+
+	fnvlist_add_uint64_array(nvx, ZPOOL_CONFIG_VDEV_ASYNC_AGG_R_HISTO,
+	    vsx->vsx_agg_histo[ZIO_PRIORITY_ASYNC_READ],
+	    ARRAY_SIZE(vsx->vsx_agg_histo[ZIO_PRIORITY_ASYNC_READ]));
+
+	fnvlist_add_uint64_array(nvx, ZPOOL_CONFIG_VDEV_ASYNC_AGG_W_HISTO,
+	    vsx->vsx_agg_histo[ZIO_PRIORITY_ASYNC_WRITE],
+	    ARRAY_SIZE(vsx->vsx_agg_histo[ZIO_PRIORITY_ASYNC_WRITE]));
+
+	fnvlist_add_uint64_array(nvx, ZPOOL_CONFIG_VDEV_AGG_SCRUB_HISTO,
+	    vsx->vsx_agg_histo[ZIO_PRIORITY_SCRUB],
+	    ARRAY_SIZE(vsx->vsx_agg_histo[ZIO_PRIORITY_SCRUB]));
+
 	/* Add extended stats nvlist to main nvlist */
 	fnvlist_add_nvlist(nv, ZPOOL_CONFIG_VDEV_STATS_EX, nvx);
 
diff --git a/tests/zfs-tests/tests/functional/cli_user/zpool_iostat/zpool_iostat_003_neg.ksh b/tests/zfs-tests/tests/functional/cli_user/zpool_iostat/zpool_iostat_003_neg.ksh
index ae1e5a152..097be9e74 100755
--- a/tests/zfs-tests/tests/functional/cli_user/zpool_iostat/zpool_iostat_003_neg.ksh
+++ b/tests/zfs-tests/tests/functional/cli_user/zpool_iostat/zpool_iostat_003_neg.ksh
@@ -52,7 +52,8 @@ fi
 
 set -A args "" "-?" "-f" "nonexistpool" "$TESTPOOL/$TESTFS" \
 	"$testpool 0" "$testpool -1" "$testpool 1 0" \
-	"$testpool 0 0" "$testpool -wl" "$testpool -wq"
+	"$testpool 0 0" "$testpool -wl" "$testpool -wq" "$testpool -wr" \
+	"$testpool -rq" "$testpool -lr"
 
 log_assert "Executing 'zpool iostat' with bad options fails"
 
diff --git a/tests/zfs-tests/tests/functional/cli_user/zpool_iostat/zpool_iostat_004_pos.ksh b/tests/zfs-tests/tests/functional/cli_user/zpool_iostat/zpool_iostat_004_pos.ksh
index f8bd8e3db..0119a7061 100755
--- a/tests/zfs-tests/tests/functional/cli_user/zpool_iostat/zpool_iostat_004_pos.ksh
+++ b/tests/zfs-tests/tests/functional/cli_user/zpool_iostat/zpool_iostat_004_pos.ksh
@@ -36,7 +36,7 @@
 #
 # DESCRIPTION:
 # Executing 'zpool iostat' command with various combinations of extended
-# stats (-vqL), parsable/script options (-pH), and misc lists of pools
+# stats (-lqwr), parsable/script options (-pH), and misc lists of pools
 # and vdevs.
 #
 # STRATEGY:
@@ -59,7 +59,9 @@ set -A args "" "-v" "-q" "-l" "-lq $TESTPOOL" "-ql ${DISKS[0]} ${DISKS[1]}" \
 	"-wp $TESTPOOL" \
 	"-qlH $TESTPOOL ${DISKS[0]}" \
 	"-vpH ${DISKS[0]}" \
-	"-wpH ${DISKS[0]}"
+	"-wpH ${DISKS[0]}" \
+	"-r ${DISKS[0]}" \
+	"-rpH ${DISKS[0]}"
 
 log_assert "Executing 'zpool iostat' with extended stat options succeeds"
 log_note "testpool: $TESTPOOL, disks $DISKS"