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From: Shaohua Li <shli@fb.com>
To: <linux-block@vger.kernel.org>, <linux-kernel@vger.kernel.org>
Cc: <kernel-team@fb.com>, <axboe@fb.com>, <tj@kernel.org>,
	<vgoyal@redhat.com>
Subject: [PATCH V5 08/17] blk-throttle: make throtl_slice tunable
Date: Thu, 15 Dec 2016 12:32:59 -0800	[thread overview]
Message-ID: <3341ed56034ecbcdaaaa63a87345ea7f16178339.1481833017.git.shli@fb.com> (raw)
In-Reply-To: <cover.1481833017.git.shli@fb.com>

throtl_slice is important for blk-throttling. It's called slice
internally but it really is a time window blk-throttling samples data.
blk-throttling will make decision based on the samplings. An example is
bandwidth measurement. A cgroup's bandwidth is measured in the time
interval of throtl_slice.

A small throtl_slice meanse cgroups have smoother throughput but burn
more CPUs. It has 100ms default value, which is not appropriate for all
disks. A fast SSD can dispatch a lot of IOs in 100ms. This patch makes
it tunable.

Since throtl_slice isn't a time slice, the sysfs name
'throttle_sample_time' reflects its character better.

Signed-off-by: Shaohua Li <shli@fb.com>
---
 Documentation/block/queue-sysfs.txt |  6 +++
 block/blk-sysfs.c                   | 10 +++++
 block/blk-throttle.c                | 77 ++++++++++++++++++++++++++-----------
 block/blk.h                         |  3 ++
 4 files changed, 74 insertions(+), 22 deletions(-)

diff --git a/Documentation/block/queue-sysfs.txt b/Documentation/block/queue-sysfs.txt
index 5164215..91f371d 100644
--- a/Documentation/block/queue-sysfs.txt
+++ b/Documentation/block/queue-sysfs.txt
@@ -192,5 +192,11 @@ scaling back writes. Writing a value of '0' to this file disables the
 feature. Writing a value of '-1' to this file resets the value to the
 default setting.
 
+throttle_sample_time (RW)
+-------------------------
+This is the time window that blk-throttle samples data, in millisecond.
+blk-throttle makes decision based on the samplings. Lower time means cgroups
+have more smooth throughput, but higher CPU overhead. This exists only when
+CONFIG_BLK_DEV_THROTTLING is enabled.
 
 Jens Axboe <jens.axboe@oracle.com>, February 2009
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index 1dbce05..0e3fb2a 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -690,6 +690,13 @@ static struct queue_sysfs_entry queue_wb_lat_entry = {
 	.show = queue_wb_lat_show,
 	.store = queue_wb_lat_store,
 };
+#ifdef CONFIG_BLK_DEV_THROTTLING
+static struct queue_sysfs_entry throtl_sample_time_entry = {
+	.attr = {.name = "throttle_sample_time", .mode = S_IRUGO | S_IWUSR },
+	.show = blk_throtl_sample_time_show,
+	.store = blk_throtl_sample_time_store,
+};
+#endif
 
 static struct attribute *default_attrs[] = {
 	&queue_requests_entry.attr,
@@ -724,6 +731,9 @@ static struct attribute *default_attrs[] = {
 	&queue_stats_entry.attr,
 	&queue_wb_lat_entry.attr,
 	&queue_poll_delay_entry.attr,
+#ifdef CONFIG_BLK_DEV_THROTTLING
+	&throtl_sample_time_entry.attr,
+#endif
 	NULL,
 };
 
diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 41ec72c..cd10c65 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -19,7 +19,8 @@ static int throtl_grp_quantum = 8;
 static int throtl_quantum = 32;
 
 /* Throttling is performed over 100ms slice and after that slice is renewed */
-static unsigned long throtl_slice = HZ/10;	/* 100 ms */
+#define DFL_THROTL_SLICE (HZ / 10)
+#define MAX_THROTL_SLICE (HZ / 5)
 
 static struct blkcg_policy blkcg_policy_throtl;
 
@@ -162,6 +163,8 @@ struct throtl_data
 	/* Total Number of queued bios on READ and WRITE lists */
 	unsigned int nr_queued[2];
 
+	unsigned int throtl_slice;
+
 	/* Work for dispatching throttled bios */
 	struct work_struct dispatch_work;
 	unsigned int limit_index;
@@ -588,7 +591,7 @@ static void throtl_dequeue_tg(struct throtl_grp *tg)
 static void throtl_schedule_pending_timer(struct throtl_service_queue *sq,
 					  unsigned long expires)
 {
-	unsigned long max_expire = jiffies + 8 * throtl_slice;
+	unsigned long max_expire = jiffies + 8 * sq_to_tg(sq)->td->throtl_slice;
 
 	if (time_after(expires, max_expire))
 		expires = max_expire;
@@ -649,7 +652,7 @@ static inline void throtl_start_new_slice_with_credit(struct throtl_grp *tg,
 	if (time_after_eq(start, tg->slice_start[rw]))
 		tg->slice_start[rw] = start;
 
-	tg->slice_end[rw] = jiffies + throtl_slice;
+	tg->slice_end[rw] = jiffies + tg->td->throtl_slice;
 	throtl_log(&tg->service_queue,
 		   "[%c] new slice with credit start=%lu end=%lu jiffies=%lu",
 		   rw == READ ? 'R' : 'W', tg->slice_start[rw],
@@ -661,7 +664,7 @@ static inline void throtl_start_new_slice(struct throtl_grp *tg, bool rw)
 	tg->bytes_disp[rw] = 0;
 	tg->io_disp[rw] = 0;
 	tg->slice_start[rw] = jiffies;
-	tg->slice_end[rw] = jiffies + throtl_slice;
+	tg->slice_end[rw] = jiffies + tg->td->throtl_slice;
 	throtl_log(&tg->service_queue,
 		   "[%c] new slice start=%lu end=%lu jiffies=%lu",
 		   rw == READ ? 'R' : 'W', tg->slice_start[rw],
@@ -671,13 +674,13 @@ static inline void throtl_start_new_slice(struct throtl_grp *tg, bool rw)
 static inline void throtl_set_slice_end(struct throtl_grp *tg, bool rw,
 					unsigned long jiffy_end)
 {
-	tg->slice_end[rw] = roundup(jiffy_end, throtl_slice);
+	tg->slice_end[rw] = roundup(jiffy_end, tg->td->throtl_slice);
 }
 
 static inline void throtl_extend_slice(struct throtl_grp *tg, bool rw,
 				       unsigned long jiffy_end)
 {
-	tg->slice_end[rw] = roundup(jiffy_end, throtl_slice);
+	tg->slice_end[rw] = roundup(jiffy_end, tg->td->throtl_slice);
 	throtl_log(&tg->service_queue,
 		   "[%c] extend slice start=%lu end=%lu jiffies=%lu",
 		   rw == READ ? 'R' : 'W', tg->slice_start[rw],
@@ -717,19 +720,20 @@ static inline void throtl_trim_slice(struct throtl_grp *tg, bool rw)
 	 * is bad because it does not allow new slice to start.
 	 */
 
-	throtl_set_slice_end(tg, rw, jiffies + throtl_slice);
+	throtl_set_slice_end(tg, rw, jiffies + tg->td->throtl_slice);
 
 	time_elapsed = jiffies - tg->slice_start[rw];
 
-	nr_slices = time_elapsed / throtl_slice;
+	nr_slices = time_elapsed / tg->td->throtl_slice;
 
 	if (!nr_slices)
 		return;
-	tmp = tg_bps_limit(tg, rw) * throtl_slice * nr_slices;
+	tmp = tg_bps_limit(tg, rw) * tg->td->throtl_slice * nr_slices;
 	do_div(tmp, HZ);
 	bytes_trim = tmp;
 
-	io_trim = (tg_iops_limit(tg, rw) * throtl_slice * nr_slices) / HZ;
+	io_trim = (tg_iops_limit(tg, rw) * tg->td->throtl_slice * nr_slices) /
+		HZ;
 
 	if (!bytes_trim && !io_trim)
 		return;
@@ -744,7 +748,7 @@ static inline void throtl_trim_slice(struct throtl_grp *tg, bool rw)
 	else
 		tg->io_disp[rw] = 0;
 
-	tg->slice_start[rw] += nr_slices * throtl_slice;
+	tg->slice_start[rw] += nr_slices * tg->td->throtl_slice;
 
 	throtl_log(&tg->service_queue,
 		   "[%c] trim slice nr=%lu bytes=%llu io=%lu start=%lu end=%lu jiffies=%lu",
@@ -764,9 +768,9 @@ static bool tg_with_in_iops_limit(struct throtl_grp *tg, struct bio *bio,
 
 	/* Slice has just started. Consider one slice interval */
 	if (!jiffy_elapsed)
-		jiffy_elapsed_rnd = throtl_slice;
+		jiffy_elapsed_rnd = tg->td->throtl_slice;
 
-	jiffy_elapsed_rnd = roundup(jiffy_elapsed_rnd, throtl_slice);
+	jiffy_elapsed_rnd = roundup(jiffy_elapsed_rnd, tg->td->throtl_slice);
 
 	/*
 	 * jiffy_elapsed_rnd should not be a big value as minimum iops can be
@@ -813,9 +817,9 @@ static bool tg_with_in_bps_limit(struct throtl_grp *tg, struct bio *bio,
 
 	/* Slice has just started. Consider one slice interval */
 	if (!jiffy_elapsed)
-		jiffy_elapsed_rnd = throtl_slice;
+		jiffy_elapsed_rnd = tg->td->throtl_slice;
 
-	jiffy_elapsed_rnd = roundup(jiffy_elapsed_rnd, throtl_slice);
+	jiffy_elapsed_rnd = roundup(jiffy_elapsed_rnd, tg->td->throtl_slice);
 
 	tmp = tg_bps_limit(tg, rw) * jiffy_elapsed_rnd;
 	do_div(tmp, HZ);
@@ -881,8 +885,10 @@ static bool tg_may_dispatch(struct throtl_grp *tg, struct bio *bio,
 	if (throtl_slice_used(tg, rw) && !(tg->service_queue.nr_queued[rw]))
 		throtl_start_new_slice(tg, rw);
 	else {
-		if (time_before(tg->slice_end[rw], jiffies + throtl_slice))
-			throtl_extend_slice(tg, rw, jiffies + throtl_slice);
+		if (time_before(tg->slice_end[rw],
+		    jiffies + tg->td->throtl_slice))
+			throtl_extend_slice(tg, rw,
+				jiffies + tg->td->throtl_slice);
 	}
 
 	if (tg_with_in_bps_limit(tg, bio, &bps_wait) &&
@@ -1601,7 +1607,7 @@ static bool throtl_can_upgrade(struct throtl_data *td,
 	if (td->limit_index != LIMIT_LOW)
 		return false;
 
-	if (time_before(jiffies, td->low_downgrade_time + throtl_slice))
+	if (time_before(jiffies, td->low_downgrade_time + td->throtl_slice))
 		return false;
 
 	rcu_read_lock();
@@ -1658,8 +1664,9 @@ static bool throtl_tg_can_downgrade(struct throtl_grp *tg)
 	 * If cgroup is below low limit, consider downgrade and throttle other
 	 * cgroups
 	 */
-	if (time_after_eq(now, td->low_upgrade_time + throtl_slice) &&
-	    time_after_eq(now, tg_last_low_overflow_time(tg) + throtl_slice))
+	if (time_after_eq(now, td->low_upgrade_time + td->throtl_slice) &&
+	    time_after_eq(now, tg_last_low_overflow_time(tg) +
+					td->throtl_slice))
 		return true;
 	return false;
 }
@@ -1689,13 +1696,14 @@ static void throtl_downgrade_check(struct throtl_grp *tg)
 		return;
 	if (!list_empty(&tg_to_blkg(tg)->blkcg->css.children))
 		return;
-	if (time_after(tg->last_check_time + throtl_slice, now))
+	if (time_after(tg->last_check_time + tg->td->throtl_slice, now))
 		return;
 
 	elapsed_time = now - tg->last_check_time;
 	tg->last_check_time = now;
 
-	if (time_before(now, tg_last_low_overflow_time(tg) + throtl_slice))
+	if (time_before(now, tg_last_low_overflow_time(tg) +
+			tg->td->throtl_slice))
 		return;
 
 	if (tg->bps[READ][LIMIT_LOW] != U64_MAX) {
@@ -1923,6 +1931,7 @@ int blk_throtl_init(struct request_queue *q)
 
 	q->td = td;
 	td->queue = q;
+	td->throtl_slice = DFL_THROTL_SLICE;
 
 	td->limit_valid[LIMIT_MAX] = true;
 	td->limit_index = LIMIT_MAX;
@@ -1943,6 +1952,30 @@ void blk_throtl_exit(struct request_queue *q)
 	kfree(q->td);
 }
 
+ssize_t blk_throtl_sample_time_show(struct request_queue *q, char *page)
+{
+	if (!q->td)
+		return -EINVAL;
+	return sprintf(page, "%u\n", jiffies_to_msecs(q->td->throtl_slice));
+}
+
+ssize_t blk_throtl_sample_time_store(struct request_queue *q,
+	const char *page, size_t count)
+{
+	unsigned long v;
+	unsigned long t;
+
+	if (!q->td)
+		return -EINVAL;
+	if (kstrtoul(page, 10, &v))
+		return -EINVAL;
+	t = msecs_to_jiffies(v);
+	if (t == 0 || t > MAX_THROTL_SLICE)
+		return -EINVAL;
+	q->td->throtl_slice = t;
+	return count;
+}
+
 static int __init throtl_init(void)
 {
 	kthrotld_workqueue = alloc_workqueue("kthrotld", WQ_MEM_RECLAIM, 0);
diff --git a/block/blk.h b/block/blk.h
index 041185e..e83e757 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -290,6 +290,9 @@ static inline struct io_context *create_io_context(gfp_t gfp_mask, int node)
 extern void blk_throtl_drain(struct request_queue *q);
 extern int blk_throtl_init(struct request_queue *q);
 extern void blk_throtl_exit(struct request_queue *q);
+extern ssize_t blk_throtl_sample_time_show(struct request_queue *q, char *page);
+extern ssize_t blk_throtl_sample_time_store(struct request_queue *q,
+	const char *page, size_t count);
 #else /* CONFIG_BLK_DEV_THROTTLING */
 static inline void blk_throtl_drain(struct request_queue *q) { }
 static inline int blk_throtl_init(struct request_queue *q) { return 0; }
-- 
2.9.3

  parent reply	other threads:[~2016-12-15 20:37 UTC|newest]

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-12-15 20:32 [PATCH V5 00/17] blk-throttle: add .low limit Shaohua Li
2016-12-15 20:32 ` [PATCH V5 01/17] blk-throttle: use U64_MAX/UINT_MAX to replace -1 Shaohua Li
2016-12-15 20:32 ` [PATCH V5 02/17] blk-throttle: prepare support multiple limits Shaohua Li
2016-12-15 20:32 ` [PATCH V5 03/17] blk-throttle: add .low interface Shaohua Li
2017-01-09 16:35   ` Tejun Heo
2016-12-15 20:32 ` [PATCH V5 04/17] blk-throttle: configure bps/iops limit for cgroup in low limit Shaohua Li
2017-01-09 17:35   ` Tejun Heo
2016-12-15 20:32 ` [PATCH V5 05/17] blk-throttle: add upgrade logic for LIMIT_LOW state Shaohua Li
2017-01-09 18:40   ` Tejun Heo
2017-01-09 19:46     ` Tejun Heo
2016-12-15 20:32 ` [PATCH V5 06/17] blk-throttle: add downgrade logic Shaohua Li
2016-12-15 20:32 ` [PATCH V5 07/17] blk-throttle: make sure expire time isn't too big Shaohua Li
2017-01-09 19:54   ` Tejun Heo
2016-12-15 20:32 ` Shaohua Li [this message]
2017-01-09 20:08   ` [PATCH V5 08/17] blk-throttle: make throtl_slice tunable Tejun Heo
2016-12-15 20:33 ` [PATCH V5 09/17] blk-throttle: detect completed idle cgroup Shaohua Li
2017-01-09 20:13   ` Tejun Heo
2016-12-15 20:33 ` [PATCH V5 10/17] blk-throttle: make bandwidth change smooth Shaohua Li
2017-01-09 20:28   ` Tejun Heo
2016-12-15 20:33 ` [PATCH V5 11/17] blk-throttle: add a simple idle detection Shaohua Li
2017-01-09 20:56   ` Tejun Heo
2016-12-15 20:33 ` [PATCH V5 12/17] blk-throttle: add interface to configure idle time threshold Shaohua Li
2017-01-09 20:58   ` Tejun Heo
2016-12-15 20:33 ` [PATCH V5 13/17] blk-throttle: ignore idle cgroup limit Shaohua Li
2017-01-09 21:01   ` Tejun Heo
2016-12-15 20:33 ` [PATCH V5 14/17] blk-throttle: add interface for per-cgroup target latency Shaohua Li
2017-01-09 21:14   ` Tejun Heo
2016-12-15 20:33 ` [PATCH V5 15/17] block: track request size in blk_issue_stat Shaohua Li
2016-12-16  2:01   ` kbuild test robot
2017-01-09 21:17   ` Tejun Heo
2016-12-15 20:33 ` [PATCH V5 16/17] blk-throttle: add a mechanism to estimate IO latency Shaohua Li
2017-01-09 21:39   ` Tejun Heo
2016-12-15 20:33 ` [PATCH V5 17/17] blk-throttle: add latency target support Shaohua Li
2017-01-09 21:46 ` [PATCH V5 00/17] blk-throttle: add .low limit Tejun Heo
2017-01-09 22:27   ` Shaohua Li

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