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Groups > linux.kernel > #1543053

[PATCH V5 09/17] blk-throttle: detect completed idle cgroup

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cgroup could be assigned a limit, but doesn't dispatch enough IO, eg the
cgroup is idle. When this happens, the cgroup doesn't hit its limit, so
we can't move the state machine to higher level and all cgroups will be
throttled to their lower limit, so we waste bandwidth. Detecting idle
cgroup is hard. This patch handles a simple case, a cgroup doesn't
dispatch any IO. We ignore such cgroup's limit, so other cgroups can use
the bandwidth.

Signed-off-by: Shaohua Li <shli@fb.com>
---
 block/blk-throttle.c | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index cd10c65..a0ba961 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -148,6 +148,8 @@ struct throtl_grp {
 
 	unsigned long last_check_time;
 
+	unsigned long last_dispatch_time[2];
+
 	/* When did we start a new slice */
 	unsigned long slice_start[2];
 	unsigned long slice_end[2];
@@ -437,11 +439,14 @@ static void tg_update_has_rules(struct throtl_grp *tg)
 
 static void throtl_pd_online(struct blkg_policy_data *pd)
 {
+	struct throtl_grp *tg = pd_to_tg(pd);
 	/*
 	 * We don't want new groups to escape the limits of its ancestors.
 	 * Update has_rules[] after a new group is brought online.
 	 */
-	tg_update_has_rules(pd_to_tg(pd));
+	tg_update_has_rules(tg);
+	tg->last_dispatch_time[READ] = jiffies;
+	tg->last_dispatch_time[WRITE] = jiffies;
 }
 
 static void blk_throtl_update_valid_limit(struct throtl_data *td)
@@ -1582,6 +1587,12 @@ static bool throtl_tg_can_upgrade(struct throtl_grp *tg)
 	if (write_limit && sq->nr_queued[WRITE] &&
 	    (!read_limit || sq->nr_queued[READ]))
 		return true;
+
+	if (time_after_eq(jiffies,
+	     tg->last_dispatch_time[READ] + tg->td->throtl_slice) &&
+	    time_after_eq(jiffies,
+	     tg->last_dispatch_time[WRITE] + tg->td->throtl_slice))
+		return true;
 	return false;
 }
 
@@ -1660,6 +1671,11 @@ static bool throtl_tg_can_downgrade(struct throtl_grp *tg)
 	struct throtl_data *td = tg->td;
 	unsigned long now = jiffies;
 
+	if (time_after_eq(now, tg->last_dispatch_time[READ] +
+					td->throtl_slice) &&
+	    time_after_eq(now, tg->last_dispatch_time[WRITE] +
+					td->throtl_slice))
+		return false;
 	/*
 	 * If cgroup is below low limit, consider downgrade and throttle other
 	 * cgroups
@@ -1769,6 +1785,7 @@ bool blk_throtl_bio(struct request_queue *q, struct blkcg_gq *blkg,
 
 again:
 	while (true) {
+		tg->last_dispatch_time[rw] = jiffies;
 		if (tg->last_low_overflow_time[rw] == 0)
 			tg->last_low_overflow_time[rw] = jiffies;
 		throtl_downgrade_check(tg);
-- 
2.9.3

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[PATCH V5 00/17] blk-throttle: add .low limit Shaohua Li <shli@fb.com> - 2016-12-15 21:40 +0100
  [PATCH V5 14/17] blk-throttle: add interface for per-cgroup target latency Shaohua Li <shli@fb.com> - 2016-12-15 21:40 +0100
  [PATCH V5 15/17] block: track request size in blk_issue_stat Shaohua Li <shli@fb.com> - 2016-12-15 21:40 +0100
  [PATCH V5 17/17] blk-throttle: add latency target support Shaohua Li <shli@fb.com> - 2016-12-15 21:40 +0100
  [PATCH V5 11/17] blk-throttle: add a simple idle detection Shaohua Li <shli@fb.com> - 2016-12-15 21:40 +0100
  [PATCH V5 08/17] blk-throttle: make throtl_slice tunable Shaohua Li <shli@fb.com> - 2016-12-15 21:40 +0100
  [PATCH V5 12/17] blk-throttle: add interface to configure idle time threshold Shaohua Li <shli@fb.com> - 2016-12-15 21:40 +0100
  [PATCH V5 09/17] blk-throttle: detect completed idle cgroup Shaohua Li <shli@fb.com> - 2016-12-15 21:40 +0100
  [PATCH V5 13/17] blk-throttle: ignore idle cgroup limit Shaohua Li <shli@fb.com> - 2016-12-15 21:40 +0100
  [PATCH V5 04/17] blk-throttle: configure bps/iops limit for cgroup in low limit Shaohua Li <shli@fb.com> - 2016-12-15 21:40 +0100
  [PATCH V5 03/17] blk-throttle: add .low interface Shaohua Li <shli@fb.com> - 2016-12-15 21:40 +0100
  [PATCH V5 02/17] blk-throttle: prepare support multiple limits Shaohua Li <shli@fb.com> - 2016-12-15 21:40 +0100
  [PATCH V5 01/17] blk-throttle: use U64_MAX/UINT_MAX to replace -1 Shaohua Li <shli@fb.com> - 2016-12-15 21:40 +0100
  [PATCH V5 10/17] blk-throttle: make bandwidth change smooth Shaohua Li <shli@fb.com> - 2016-12-15 21:40 +0100

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