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

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 <>
parent feffa5cc
......@@ -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 <>, February 2009
......@@ -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;
if (val == -1)
rwb->min_lat_nsec = wbt_default_latency_nsec(q);
else if (val >= 0)
rwb->min_lat_nsec = val * 1000ULL;
return -EINVAL;
return count;
......@@ -675,6 +675,18 @@ void wbt_disable(struct rq_wb *rwb)
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;
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;
if (blk_queue_nonrot(q))
rwb->min_lat_nsec = 2000000ULL;
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));
......@@ -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 *);
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 */
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