[PATCH V2 07/11] blk-throttle: make throtl_slice tunable

From: Shaohua Li
Date: Thu Sep 15 2016 - 12:24:15 EST

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throtl_slice is important for blk-throttling. A lot of stuffes depend on
it, for example, throughput measurement. It has 100ms default value,
which is not appropriate for all disks. For example, for SSD we might
use a smaller value to make the throughput smoother. This patch makes it
tunable.

Signed-off-by: Shaohua Li <shli@xxxxxx>
---
block/blk-sysfs.c | 11 ++++++++
block/blk-throttle.c | 72 ++++++++++++++++++++++++++++++++++++----------------
block/blk.h | 3 +++
3 files changed, 64 insertions(+), 22 deletions(-)

diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index f87a7e7..610f08d 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -526,6 +526,14 @@ static struct queue_sysfs_entry queue_dax_entry = {
.show = queue_dax_show,
};

+#ifdef CONFIG_BLK_DEV_THROTTLING
+static struct queue_sysfs_entry throtl_slice_entry = {
+ .attr = {.name = "throttling_slice", .mode = S_IRUGO | S_IWUSR },
+ .show = blk_throtl_slice_show,
+ .store = blk_throtl_slice_store,
+};
+#endif
+
static struct attribute *default_attrs[] = {
&queue_requests_entry.attr,
&queue_ra_entry.attr,
@@ -553,6 +561,9 @@ static struct attribute *default_attrs[] = {
&queue_poll_entry.attr,
&queue_wc_entry.attr,
&queue_dax_entry.attr,
+#ifdef CONFIG_BLK_DEV_THROTTLING
+ &throtl_slice_entry.attr,
+#endif
NULL,
};

diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 2bd8333..bc94086 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;

@@ -158,6 +159,8 @@ 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;
@@ -589,7 +592,7 @@ 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;
mod_timer(&sq->pending_timer, expires);
@@ -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 +720,19 @@ 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 +747,7 @@ 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 +767,9 @@ 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 +816,9 @@ 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);
@@ -878,8 +881,8 @@ static bool tg_may_dispatch(struct throtl_grp *tg, struct bio *bio,
if (throtl_slice_used(tg, 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 +1631,7 @@ static bool throtl_can_upgrade(struct throtl_data *td,
if (td->limit_index != LIMIT_HIGH)
return false;

- if (time_before(jiffies, td->high_downgrade_time + throtl_slice))
+ if (time_before(jiffies, td->high_downgrade_time + td->throtl_slice))
return false;

rcu_read_lock();
@@ -1685,8 +1688,8 @@ static bool throtl_downgrade_check_one(struct throtl_grp *tg)
* If cgroup is below high limit, consider downgrade and throttle other
* cgroups
*/
- if (time_after_eq(now, td->high_upgrade_time + throtl_slice) &&
- time_after_eq(now, tg_last_high_overflow_time(tg) + throtl_slice))
+ if (time_after_eq(now, td->high_upgrade_time + td->throtl_slice) &&
+ time_after_eq(now, tg_last_high_overflow_time(tg) + td->throtl_slice))
return true;
return false;
}
@@ -1719,10 +1722,10 @@ 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;

- if (time_before(now, tg_last_high_overflow_time(tg) + throtl_slice))
+ if (time_before(now, tg_last_high_overflow_time(tg) + tg->td->throtl_slice))
return;

elapsed_time = now - tg->last_check_time;
@@ -1960,6 +1963,7 @@ int blk_throtl_init(struct request_queue *q)

q->td = td;
td->queue = q;
+ td->throtl_slice = DFL_THROTL_SLICE;

td->limit_valid[LIMIT_HIGH] = false;
td->limit_valid[LIMIT_MAX] = true;
@@ -1981,6 +1985,30 @@ void blk_throtl_exit(struct request_queue *q)
kfree(q->td);
}

+ssize_t blk_throtl_slice_show(struct request_queue *q, char *page)
+{
+ if (!q->td)
+ return -EINVAL;
+ return sprintf(page, "%ums\n", jiffies_to_msecs(q->td->throtl_slice));
+}
+
+ssize_t blk_throtl_slice_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 c37492f..8ad6068 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -294,6 +294,9 @@ 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_slice_show(struct request_queue *q, char *page);
+extern ssize_t blk_throtl_slice_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; }
--
2.8.0.rc2

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