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Date: Mon, 9 Apr 2018 14:15:46 +0800
From: Jianchao Wang <jianchao.w.wang@...cle.com>
To: axboe@...nel.dk, shli@...com
Cc: linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] blk-throttle: discard stale last_low_overflow_time
When there is only one type of traffic, the associated
last_low_overflow_time will not be updated, so the value is
stale and invalid and we should discard it. Otherwise,
__tg_last_low_overflow_time always return the stale value because
it is smaller, and then we always get bps/iops has been below low
limit for 1 throtl_slice, and limit_index will jump down and up
between LOW and MAX, the actual bps/iops stays on low_limit.
Add last_submit_time[2] into tg to track the time when bio enters
into blk_throtl_bio. If there is no bio entering during past 5
throtl_slices, and the actual dispatching bps/iops are indeed lower
than low limit, return 0 as the last_low_overflow_time which
indicates it is stale. We will discard the stale last_low_overflow_time,
but if both types are stale, return 0, Otherwise, the cgroups which
don't have any traffic will prevent upgrade.
Signed-off-by: Jianchao Wang <jianchao.w.wang@...cle.com>
---
block/blk-throttle.c | 37 ++++++++++++++++++++++++++++++++++---
1 file changed, 34 insertions(+), 3 deletions(-)
diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index c5a1316..851aa16 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -158,6 +158,7 @@ struct throtl_grp {
unsigned int io_disp[2];
unsigned long last_low_overflow_time[2];
+ unsigned long last_submit_time[2];
uint64_t last_bytes_disp[2];
unsigned int last_io_disp[2];
@@ -1752,15 +1753,42 @@ static struct blkcg_policy blkcg_policy_throtl = {
.pd_free_fn = throtl_pd_free,
};
+/*
+ * If there is no any traffic of type 'rw' into blk_throtl_bio during
+ * past 5 throtl_slice, AND the actual dispatching bps/iops of type 'rw'
+ * is indeed lower than low limit, we return 0 as the last_low_overflow_time
+ * which indicates it is stale.
+ */
+static inline unsigned long tg_return_lloft(struct throtl_grp *tg,
+ unsigned int rw)
+{
+ unsigned long time = tg->last_low_overflow_time[rw];
+ unsigned long now = jiffies;
+
+ if (!time_after(now,
+ tg->last_submit_time[rw] + 5 * tg->td->throtl_slice))
+ return time;
+
+ if (!time_after(now, time + 5 * tg->td->throtl_slice))
+ return time;
+
+ return 0;
+}
+
static unsigned long __tg_last_low_overflow_time(struct throtl_grp *tg)
{
unsigned long rtime = jiffies, wtime = jiffies;
if (tg->bps[READ][LIMIT_LOW] || tg->iops[READ][LIMIT_LOW])
- rtime = tg->last_low_overflow_time[READ];
+ rtime = tg_return_lloft(tg, READ);
if (tg->bps[WRITE][LIMIT_LOW] || tg->iops[WRITE][LIMIT_LOW])
- wtime = tg->last_low_overflow_time[WRITE];
- return min(rtime, wtime);
+ wtime = tg_return_lloft(tg, WRITE);
+
+ /*
+ * A cgroup w/o any traffic could have two stale value, return 0 instead
+ * of 'now', otherwise, it will prevent upgrade.
+ */
+ return (rtime && wtime) ? min(rtime, wtime) : (rtime + wtime);
}
/* tg should not be an intermediate node */
@@ -2175,8 +2203,11 @@ bool blk_throtl_bio(struct request_queue *q, struct blkcg_gq *blkg,
while (true) {
if (tg->last_low_overflow_time[rw] == 0)
tg->last_low_overflow_time[rw] = jiffies;
+ if (unlikely(tg->last_submit_time[rw] == 0))
+ tg->last_submit_time[rw] = jiffies;
throtl_downgrade_check(tg);
throtl_upgrade_check(tg);
+ tg->last_submit_time[rw] = jiffies;
/* throtl is FIFO - if bios are already queued, should queue */
if (sq->nr_queued[rw])
break;
--
2.7.4
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