Commit 80e091d1 authored by Jens Axboe's avatar Jens Axboe
Browse files

blk-wbt: allow reset of default latency through sysfs 



Allow a write of '-1' to reset the default latency target for
a given device. This removes knowledge of the different default
settings for rotational vs non-rotational from user space.

Signed-off-by: default avatarJens Axboe <axboe@fb.com>
parent feffa5cc

Documentation/block/queue-sysfs.txt

+3 −1
Original line number Diff line number Diff line
@@ -188,7 +188,9 @@ wb_lat_usec (RW) 
If the device is registered for writeback throttling, then this file shows

the target minimum read latency. If this latency is exceeded in a given

window of time (see wb_window_usec), then the writeback throttling will start

scaling back writes.

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.





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

block/blk-sysfs.c

+15 −7
Original line number Diff line number Diff line
@@ -42,12 +42,12 @@ queue_var_store(unsigned long *var, const char *page, size_t count) 
	return count;

}



static ssize_t queue_var_store64(u64 *var, const char *page)

static ssize_t queue_var_store64(s64 *var, const char *page)

{

	int err;

	u64 v;

	s64 v;



	err = kstrtou64(page, 10, &v);

	err = kstrtos64(page, 10, &v);

	if (err < 0)

		return err;
@@ -421,18 +421,26 @@ static ssize_t queue_wb_lat_show(struct request_queue *q, char *page) 
static ssize_t queue_wb_lat_store(struct request_queue *q, const char *page,

				  size_t count)

{

	struct rq_wb *rwb;

	ssize_t ret;

	u64 val;

	s64 val;



	if (!q->rq_wb)

	rwb = q->rq_wb;

	if (!rwb)

		return -EINVAL;



	ret = queue_var_store64(&val, page);

	if (ret < 0)

		return ret;



	q->rq_wb->min_lat_nsec = val * 1000ULL;

	wbt_update_limits(q->rq_wb);

	if (val == -1)

		rwb->min_lat_nsec = wbt_default_latency_nsec(q);

	else if (val >= 0)

		rwb->min_lat_nsec = val * 1000ULL;

	else

		return -EINVAL;



	wbt_update_limits(rwb);

	return count;

}

block/blk-wbt.c

+13 −4
Original line number Diff line number Diff line
@@ -675,6 +675,18 @@ void wbt_disable(struct rq_wb *rwb) 
}

EXPORT_SYMBOL_GPL(wbt_disable);



u64 wbt_default_latency_nsec(struct request_queue *q)

{

	/*

	 * We default to 2msec for non-rotational storage, and 75msec

	 * for rotational storage.

	 */

	if (blk_queue_nonrot(q))

		return 2000000ULL;

	else

		return 75000000ULL;

}



int wbt_init(struct request_queue *q)

{

	struct rq_wb *rwb;
@@ -711,10 +723,7 @@ int wbt_init(struct request_queue *q) 
	q->rq_wb = rwb;

	blk_stat_enable(q);



	if (blk_queue_nonrot(q))

		rwb->min_lat_nsec = 2000000ULL;

	else

		rwb->min_lat_nsec = 75000000ULL;

	rwb->min_lat_nsec = wbt_default_latency_nsec(q);



	wbt_set_queue_depth(rwb, blk_queue_depth(q));

	wbt_set_write_cache(rwb, test_bit(QUEUE_FLAG_WC, &q->queue_flags));

block/blk-wbt.h

+6 −0
Original line number Diff line number Diff line
@@ -110,6 +110,8 @@ void wbt_disable(struct rq_wb *); 
void wbt_set_queue_depth(struct rq_wb *, unsigned int);

void wbt_set_write_cache(struct rq_wb *, bool);



u64 wbt_default_latency_nsec(struct request_queue *);



#else



static inline void __wbt_done(struct rq_wb *rwb, enum wbt_flags flags)
@@ -148,6 +150,10 @@ static inline void wbt_set_queue_depth(struct rq_wb *rwb, unsigned int depth) 
static inline void wbt_set_write_cache(struct rq_wb *rwb, bool wc)

{

}

static inline u64 wbt_default_latency_nsec(struct request_queue *q)

{

	return 0;

}



#endif /* CONFIG_BLK_WBT */