Re: [PATCH v2] cfq-iosched: fix the delay of cfq_group's vdisktime under iops mode
From: Jan Kara <jack@suse.cz>
Date: 2017-03-08 14:05:18
Also in:
stable
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: <redacted> # 4.8+
Signed-off-by: Hou Tao <redacted>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 <jack@suse.cz> Honza
quoted hunk ↗ jump to hunk
--- block/cfq-iosched.c | 17 +++++++++++++++-- 1 file changed, 15 insertions(+), 2 deletions(-) v2: - use constant instead of "nsecs_to_jiffies64(CFQ_IDLE_DELAY)" as suggested by Jan Kara v1: https://www.spinics.net/lists/stable/msg160580.htmldiff --git a/block/cfq-iosched.c b/block/cfq-iosched.c index 440b95e..69754e8 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 (200) /* * 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
-- Jan Kara [off-list ref] SUSE Labs, CR