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Subject[PATCH] io-controller: optimization for iog deletion when elevator exiting
Hi Vivek,

There's no need to travel the iocg->group_data for each iog
when exiting a elevator, that costs too much. An alternative
solution is reseting iocg_id as soon as an io group unlinking
from a iocg. Make a decision that whether it's need to carry
out deleting action by checking iocg_id.

Signed-off-by: Gui Jianfeng <guijianfeng@cn.fujitsu.com>
---
block/elevator-fq.c | 29 ++++++++++-------------------
1 files changed, 10 insertions(+), 19 deletions(-)

diff --git a/block/elevator-fq.c b/block/elevator-fq.c
index d779282..b26fe0f 100644
--- a/block/elevator-fq.c
+++ b/block/elevator-fq.c
@@ -2218,8 +2218,6 @@ void io_group_cleanup(struct io_group *iog)
BUG_ON(iog->sched_data.active_entity != NULL);
BUG_ON(entity != NULL && entity->tree != NULL);

- iog->iocg_id = 0;
-
/*
* Wait for any rcu readers to exit before freeing up the group.
* Primarily useful when io_get_io_group() is called without queue
@@ -2376,6 +2374,7 @@ remove_entry:
group_node);
efqd = rcu_dereference(iog->key);
hlist_del_rcu(&iog->group_node);
+ iog->iocg_id = 0;
spin_unlock_irqrestore(&iocg->lock, flags);

spin_lock_irqsave(efqd->queue->queue_lock, flags);
@@ -2403,35 +2402,27 @@ done:
void io_group_check_and_destroy(struct elv_fq_data *efqd, struct io_group *iog)
{
struct io_cgroup *iocg;
- unsigned short id = iog->iocg_id;
- struct hlist_node *n;
- struct io_group *__iog;
unsigned long flags;
struct cgroup_subsys_state *css;

rcu_read_lock();

- BUG_ON(!id);
- css = css_lookup(&io_subsys, id);
+ css = css_lookup(&io_subsys, iog->iocg_id);

- /* css can't go away as associated io group is still around */
- BUG_ON(!css);
+ if (!css)
+ goto out;

iocg = container_of(css, struct io_cgroup, css);

spin_lock_irqsave(&iocg->lock, flags);
- hlist_for_each_entry_rcu(__iog, n, &iocg->group_data, group_node) {
- /*
- * Remove iog only if it is still in iocg list. Cgroup
- * deletion could have deleted it already.
- */
- if (__iog == iog) {
- hlist_del_rcu(&iog->group_node);
- __io_destroy_group(efqd, iog);
- break;
- }
+
+ if (iog->iocg_id) {
+ hlist_del_rcu(&iog->group_node);
+ __io_destroy_group(efqd, iog);
}
+
spin_unlock_irqrestore(&iocg->lock, flags);
+out:
rcu_read_unlock();
}

-- 1.5.4.rc3


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