Commit 297e3d85 authored by Shaohua Li's avatar Shaohua Li Committed by Jens Axboe
Browse files

blk-throttle: make throtl_slice tunable 



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: default avatarShaohua Li <shli@fb.com>
Signed-off-by: default avatarJens Axboe <axboe@fb.com>
parent 06cceedc

Documentation/block/queue-sysfs.txt

+6 −0
Original line number Diff line number Diff line
@@ -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_LOW is enabled.



Jens Axboe <jens.axboe@oracle.com>, February 2009

block/blk-sysfs.c

+11 −0
Original line number Diff line number Diff line
@@ -677,6 +677,14 @@ static struct queue_sysfs_entry queue_wb_lat_entry = { 
	.store = queue_wb_lat_store,

};



#ifdef CONFIG_BLK_DEV_THROTTLING_LOW

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,

	&queue_ra_entry.attr,
@@ -710,6 +718,9 @@ static struct attribute *default_attrs[] = { 
	&queue_dax_entry.attr,

	&queue_wb_lat_entry.attr,

	&queue_poll_delay_entry.attr,

#ifdef CONFIG_BLK_DEV_THROTTLING_LOW

	&throtl_sample_time_entry.attr,

#endif

	NULL,

};

block/blk-throttle.c

+57 −22
Original line number Diff line number Diff line
@@ -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)



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;
@@ -590,7 +593,7 @@ 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;



	/*

	 * Since we are adjusting the throttle limit dynamically, the sleep
@@ -658,7 +661,7 @@ 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],
@@ -670,7 +673,7 @@ 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],
@@ -680,13 +683,13 @@ 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],
@@ -726,19 +729,20 @@ 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;
@@ -753,7 +757,7 @@ 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",
@@ -773,9 +777,9 @@ 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
@@ -822,9 +826,9 @@ 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);
@@ -890,8 +894,10 @@ 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) &&
@@ -1632,7 +1638,7 @@ 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();
@@ -1689,8 +1695,9 @@ 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;

}
@@ -1719,13 +1726,14 @@ 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]) {
@@ -1953,6 +1961,7 @@ 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;
@@ -1973,6 +1982,32 @@ void blk_throtl_exit(struct request_queue *q) 
	kfree(q->td);

}



#ifdef CONFIG_BLK_DEV_THROTTLING_LOW

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;

}

#endif



static int __init throtl_init(void)

{

	kthrotld_workqueue = alloc_workqueue("kthrotld", WQ_MEM_RECLAIM, 0);

block/blk.h

+5 −0
Original line number Diff line number Diff line
@@ -324,5 +324,10 @@ static inline void blk_throtl_drain(struct request_queue *q) { } 
static inline int blk_throtl_init(struct request_queue *q) { return 0; }

static inline void blk_throtl_exit(struct request_queue *q) { }

#endif /* CONFIG_BLK_DEV_THROTTLING */

#ifdef CONFIG_BLK_DEV_THROTTLING_LOW

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);

#endif



#endif /* BLK_INTERNAL_H */

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