On 2017/3/8 22:05, Jan Kara wrote:
> On Wed 08-03-17 20:16:55, Hou Tao wrote:
>> 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_queue are different things, so I define two new
>> macros for the delay of a cfq_group under time-slice mode and IOPs mode.
>>
>> Fixes: 9a7f38c42c2b92391d9dabaf9f51df7cfe5608e4
>> Cc: <[email protected]> # 4.8+
>> Signed-off-by: Hou Tao <[email protected]>
>
> OK, the number 200 is somewhat arbitrary but so is HZ/5 so I guess we are
> OK. You can add:
>
> Acked-by: Jan Kara <[email protected]>
Oops, sorry for the arbitrary 200. My intention was to use HZ / 5 instead of 200
to keep consistent with the old CFQ_IDLE_DELAY. And I spot two typos in commit
message: "the delay of cfq_queue" -> "the delay of cfq_group" and "IOPs" ->
"iops".
Jan, could you please fix them ? And I also attach a revised patch to fix them.
From: Hou Tao <[email protected]>
Date: Wed, 1 Mar 2017 09:02:33 +0800
Subject: [PATCH] cfq-iosched: fix the delay of cfq_group's vdisktime under
iops mode
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: 9a7f38c42c2b92391d9dabaf9f51df7cfe5608e4
Cc: <[email protected]> # 4.8+
Signed-off-by: Hou Tao <[email protected]>
Acked-by: Jan Kara <[email protected]>
---
block/cfq-iosched.c | 17 +++++++++++++++--
1 file changed, 15 insertions(+), 2 deletions(-)
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 440b95e..2762505 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -38,9 +38,13 @@ static const u64 cfq_target_latency = (u64)NSEC_PER_SEC *
3/10; /* 300 ms */
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
@@ -1362,6 +1366,14 @@ cfq_group_service_tree_add(struct cfq_rb_root *st,
struct cfq_group *cfqg)
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)
{
@@ -1381,7 +1393,8 @@ cfq_group_notify_queue_add(struct cfq_data *cfqd, struct
cfq_group *cfqg)
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);
--
2.5.0
