linux-kernel - [PATCH 4.9 053/119] cfq-iosched: fix the delay of cfq

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Message-Id: <20170612152600.381098923@linuxfoundation.org>
Date:   Mon, 12 Jun 2017 17:25:15 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Hou Tao <houtao1@...wei.com>,
        Jan Kara <jack@...e.cz>, Jens Axboe <axboe@...com>
Subject: [PATCH 4.9 053/119] cfq-iosched: fix the delay of cfq_groups vdisktime under iops mode

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Hou Tao <houtao1@...wei.com>

commit 5be6b75610cefd1e21b98a218211922c2feb6e08 upstream.

When adding a cfq_group into the cfq service tree, we use CFQ_IDLE_DELAY
as the delay of cfq_group's vdisktime if there have been other cfq_groups
already.

When cfq is under iops mode, commit 9a7f38c42c2b ("cfq-iosched: Convert
from jiffies to nanoseconds") could result in a large iops delay and
lead to an abnormal io schedule delay for the added cfq_group. To fix
it, we just need to revert to the old CFQ_IDLE_DELAY value: HZ / 5
when iops mode is enabled.

Despite having the same value, the delay of a cfq_queue in idle class
and the delay of cfq_group are different things, so I define two new
macros for the delay of a cfq_group under time-slice mode and iops mode.

Fixes: 9a7f38c42c2b ("cfq-iosched: Convert from jiffies to nanoseconds")
Signed-off-by: Hou Tao <houtao1@...wei.com>
Acked-by: Jan Kara <jack@...e.cz>
Signed-off-by: Jens Axboe <axboe@...com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 block/cfq-iosched.c |   17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -36,9 +36,13 @@ static const u64 cfq_target_latency = (u
 static const int cfq_hist_divisor = 4;
 
 /*
- * offset from end of service tree
+ * offset from end of queue service tree for idle class
  */
 #define CFQ_IDLE_DELAY		(NSEC_PER_SEC / 5)
+/* offset from end of group service tree under time slice mode */
+#define CFQ_SLICE_MODE_GROUP_DELAY (NSEC_PER_SEC / 5)
+/* offset from end of group service under IOPS mode */
+#define CFQ_IOPS_MODE_GROUP_DELAY (HZ / 5)
 
 /*
  * below this threshold, we consider thinktime immediate
@@ -1370,6 +1374,14 @@ cfq_group_service_tree_add(struct cfq_rb
 	cfqg->vfraction = max_t(unsigned, vfr, 1);
 }
 
+static inline u64 cfq_get_cfqg_vdisktime_delay(struct cfq_data *cfqd)
+{
+	if (!iops_mode(cfqd))
+		return CFQ_SLICE_MODE_GROUP_DELAY;
+	else
+		return CFQ_IOPS_MODE_GROUP_DELAY;
+}
+
 static void
 cfq_group_notify_queue_add(struct cfq_data *cfqd, struct cfq_group *cfqg)
 {
@@ -1389,7 +1401,8 @@ cfq_group_notify_queue_add(struct cfq_da
 	n = rb_last(&st->rb);
 	if (n) {
 		__cfqg = rb_entry_cfqg(n);
-		cfqg->vdisktime = __cfqg->vdisktime + CFQ_IDLE_DELAY;
+		cfqg->vdisktime = __cfqg->vdisktime +
+			cfq_get_cfqg_vdisktime_delay(cfqd);
 	} else
 		cfqg->vdisktime = st->min_vdisktime;
 	cfq_group_service_tree_add(st, cfqg);