Re: [PATCH] io-controller: optimization for iog deletion when elevator exiting

Vivek Goyal
2009-06-29T14:07:43Z

On Mon, Jun 29, 2009 at 01:27:47PM +0800, Gui Jianfeng wrote:
> 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.
>

Thanks Gui. This makes sense to me. We can check iog->iocg_id to determine
wheter group is still on iocg list or not instead of traversing the list.

Nauman, do you see any issues with the patch?

Thanks
Vivek

> 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