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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 9a7f38c42c ("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: 9a7f38c42c ("cfq-iosched: Convert from jiffies to nanoseconds")
Cc: <stable@vger.kernel.org> # 4.8+
Signed-off-by: Hou Tao <houtao1@huawei.com>
Acked-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@fb.com>
This commit is contained in:
Hou Tao 2017-03-01 09:02:33 +08:00 committed by Jens Axboe
parent e4dc2b32df
commit 5be6b75610
1 changed files with 15 additions and 2 deletions
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17
block/cfq-iosched.c
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@ -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);