[1/4] block: add a statistic table for io latency

Commit Message

Guoqing Jiang Jan. 27, 2021, 2:59 p.m. UTC

Usually, we get the status of block device by cat stat file, but we can
only know the total time with that file. And we would like to know more
accurate statistic, such as each latency range, which helps people to
diagnose if there is issue about the hardware.

Also a new config option is introduced to control if people want to know
the additional statistics or not, and we use the option for io sector in
next patch.

This change is based on our internal patch from Florian-Ewald Mueller
([e-mail]).

Reviewed-by: Jack Wang <[e-mail]>
Signed-off-by: Guoqing Jiang <[e-mail]>
---
 Documentation/ABI/testing/sysfs-block |  8 ++++++
 block/Kconfig                         |  8 ++++++
 block/blk-core.c                      | 29 +++++++++++++++++++
 block/genhd.c                         | 41 +++++++++++++++++++++++++++
 include/linux/part_stat.h             |  7 +++++
 5 files changed, 93 insertions(+)

Comments

Christoph Hellwig Jan. 27, 2021, 5:10 p.m. UTC | #1

On Wed, Jan 27, 2021 at 03:59:27PM +0100, Guoqing Jiang wrote:
> +config BLK_ADDITIONAL_DISKSTAT
> +	bool "Block layer additional diskstat"
> +	default n

n is the default default.  But more importantly I don't think having
this as a compile time option makes much sense sense.  No one is going
to recompile their kernel to get a few stats or to avoid the overhead
of these stats.

Guoqing Jiang Jan. 28, 2021, 2:44 a.m. UTC | #2

On 1/27/21 18:10, Christoph Hellwig wrote:
> On Wed, Jan 27, 2021 at 03:59:27PM +0100, Guoqing Jiang wrote:
>> +config BLK_ADDITIONAL_DISKSTAT
>> +	bool "Block layer additional diskstat"
>> +	default n
> 
> n is the default default.  But more importantly I don't think having
> this as a compile time option makes much sense sense.  No one is going
> to recompile their kernel to get a few stats or to avoid the overhead
> of these stats.
> 

Ok, I will just use io_extra_stats node to dynamically control the 
stats, please let me know your thought about it.

Thanks,
Guoqin

Patch

diff --git a/Documentation/ABI/testing/sysfs-block b/Documentation/ABI/testing/sysfs-block
index e34cdeeeb9d4..4371a0f2cb5e 100644
--- a/Documentation/ABI/testing/sysfs-block
+++ b/Documentation/ABI/testing/sysfs-block
@@ -27,6 +27,14 @@  Description:
 
 		For more details refer Documentation/admin-guide/iostats.rst
 
+What:		/sys/block/<disk>/io_latency
+Date:		January 2021
+Contact:	Guoqing Jiang <[e-mail]>
+Description:
+		The /sys/block/<disk>/io_latency files displays the I/O
+		latency of disk <disk>. With it, it is convenient to know
+		the statistics of I/O latency for each type (read, write,
+		discard and flush) which have happened to the disk.
 
 What:		/sys/block/<disk>/<part>/stat
 Date:		February 2008
diff --git a/block/Kconfig b/block/Kconfig
index a2297edfdde8..ca3854a7e3db 100644
--- a/block/Kconfig
+++ b/block/Kconfig
@@ -174,6 +174,14 @@  config BLK_DEBUG_FS
 	Unless you are building a kernel for a tiny system, you should
 	say Y here.
 
+config BLK_ADDITIONAL_DISKSTAT
+	bool "Block layer additional diskstat"
+	default n
+	help
+	Enabling this option adds io latency statistics for each block device.
+
+	If unsure, say N.
+
 config BLK_DEBUG_FS_ZONED
        bool
        default BLK_DEBUG_FS && BLK_DEV_ZONED
diff --git a/block/blk-core.c b/block/blk-core.c
index 5e752840b41a..27cd153e374b 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1264,6 +1264,33 @@  static void update_io_ticks(struct block_device *part, unsigned long now,
 	}
 }
 
+/*
+ * Either account additional stat for request if req is not NULL or account for bio.
+ */
+static void blk_additional_latency(struct block_device *part, const int sgrp,
+				   struct request *req, unsigned long start_jiffies)
+{
+#ifdef CONFIG_BLK_ADDITIONAL_DISKSTAT
+	unsigned int idx;
+	unsigned long duration, now = READ_ONCE(jiffies);
+
+	if (req)
+		duration = jiffies_to_nsecs(now) - req->start_time_ns;
+	else
+		duration = jiffies_to_nsecs(now - start_jiffies);
+
+	duration /= NSEC_PER_MSEC;
+	duration /= HZ_TO_MSEC_NUM;
+	if (likely(duration > 0)) {
+		idx = ilog2(duration);
+		if (idx > ADD_STAT_NUM - 1)
+			idx = ADD_STAT_NUM - 1;
+	} else
+		idx = 0;
+	part_stat_inc(part, latency_table[idx][sgrp]);
+#endif
+}
+
 static void blk_account_io_completion(struct request *req, unsigned int bytes)
 {
 	if (req->part && blk_do_io_stat(req)) {
@@ -1288,6 +1315,7 @@  void blk_account_io_done(struct request *req, u64 now)
 
 		part_stat_lock();
 		update_io_ticks(req->part, jiffies, true);
+		blk_additional_latency(req->part, sgrp, req, 0);
 		part_stat_inc(req->part, ios[sgrp]);
 		part_stat_add(req->part, nsecs[sgrp], now - req->start_time_ns);
 		part_stat_unlock();
@@ -1354,6 +1382,7 @@  static void __part_end_io_acct(struct block_device *part, unsigned int op,
 
 	part_stat_lock();
 	update_io_ticks(part, now, true);
+	blk_additional_latency(part, sgrp, NULL, start_time);
 	part_stat_add(part, nsecs[sgrp], jiffies_to_nsecs(duration));
 	part_stat_local_dec(part, in_flight[op_is_write(op)]);
 	part_stat_unlock();
diff --git a/block/genhd.c b/block/genhd.c
index d3ef29fbc536..cdbf56f05060 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -1146,6 +1146,44 @@  static struct device_attribute dev_attr_fail_timeout =
 	__ATTR(io-timeout-fail, 0644, part_timeout_show, part_timeout_store);
 #endif
 
+#ifdef CONFIG_BLK_ADDITIONAL_DISKSTAT
+static ssize_t io_latency_show(struct device *dev, struct device_attribute *attr, char *buf)
+{
+	struct block_device *bdev = dev_to_bdev(dev);
+	size_t count = 0;
+	int i, sgrp;
+
+	for (i = 0; i < ADD_STAT_NUM; i++) {
+		unsigned int from, to;
+
+		if (i == ADD_STAT_NUM - 1) {
+			count += scnprintf(buf + count, PAGE_SIZE - count, "      >= %5d  ms: ",
+					   (2 << (i - 2)) * HZ_TO_MSEC_NUM);
+		} else {
+			if (i < 2) {
+				from = i;
+				to = i + 1;
+			} else {
+				from = 2 << (i - 2);
+				to = 2 << (i - 1);
+			}
+			count += scnprintf(buf + count, PAGE_SIZE - count, "[%5d - %-5d) ms: ",
+					   from * HZ_TO_MSEC_NUM, to * HZ_TO_MSEC_NUM);
+		}
+
+		for (sgrp = 0; sgrp < NR_STAT_GROUPS; sgrp++)
+			count += scnprintf(buf + count, PAGE_SIZE - count, "%lu ",
+					   part_stat_read(bdev, latency_table[i][sgrp]));
+		count += scnprintf(buf + count, PAGE_SIZE - count, "\n");
+	}
+
+	return count;
+}
+
+static struct device_attribute dev_attr_io_latency =
+	__ATTR(io_latency, 0444, io_latency_show, NULL);
+#endif
+
 static struct attribute *disk_attrs[] = {
 	&dev_attr_range.attr,
 	&dev_attr_ext_range.attr,
@@ -1164,6 +1202,9 @@  static struct attribute *disk_attrs[] = {
 #endif
 #ifdef CONFIG_FAIL_IO_TIMEOUT
 	&dev_attr_fail_timeout.attr,
+#endif
+#ifdef CONFIG_BLK_ADDITIONAL_DISKSTAT
+	&dev_attr_io_latency.attr,
 #endif
 	NULL
 };
diff --git a/include/linux/part_stat.h b/include/linux/part_stat.h
index d2558121d48c..763953238227 100644
--- a/include/linux/part_stat.h
+++ b/include/linux/part_stat.h
@@ -9,6 +9,13 @@  struct disk_stats {
 	unsigned long sectors[NR_STAT_GROUPS];
 	unsigned long ios[NR_STAT_GROUPS];
 	unsigned long merges[NR_STAT_GROUPS];
+#ifdef CONFIG_BLK_ADDITIONAL_DISKSTAT
+	/*
+	 * We measure latency (ms) for 1, 2, ..., 1024 and >=1024.
+	 */
+#define ADD_STAT_NUM	12
+	unsigned long latency_table[ADD_STAT_NUM][NR_STAT_GROUPS];
+#endif
 	unsigned long io_ticks;
 	local_t in_flight[2];
 };