[PATCH V6 08/18] blk-throttle: make throtl_slice tunable

From: Shaohua Li
Date: Sat Jan 14 2017 - 22:45:47 EST

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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@xxxxxx>
---
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 c0a3bb5..5afebfe 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@xxxxxxxxxx>, 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 ce4094e..49cad9a 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)

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) &&
@@ -1628,7 +1634,7 @@ 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();
@@ -1685,8 +1691,9 @@ 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;
}
@@ -1715,13 +1722,14 @@ 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]) {
@@ -1949,6 +1957,7 @@ 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;
@@ -1969,6 +1978,30 @@ 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

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