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Commit 0b39920b authored by Tejun Heo's avatar Tejun Heo
Browse files

cfq-iosched: collect stats from dead cfqgs 



To support hierarchical stats, it's necessary to remember stats from
dead children.  Add cfqg->dead_stats and make a dying cfqg transfer
its stats to the parent's dead-stats.

The transfer happens form ->pd_offline_fn() and it is possible that
there are some residual IOs completing afterwards.  Currently, we lose
these stats.  Given that cgroup removal isn't a very high frequency
operation and the amount of residual IOs on offline are likely to be
nil or small, this shouldn't be a big deal and the complexity needed
to handle residual IOs - another callback and rather elaborate
synchronization to reach and lock the matching q - doesn't seem
justified.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarVivek Goyal <vgoyal@redhat.com>
parent 689665af

block/cfq-iosched.c

+56 −1
Original line number Diff line number Diff line
@@ -289,7 +289,8 @@ struct cfq_group { 
	/* number of requests that are on the dispatch list or inside driver */

	int dispatched;

	struct cfq_ttime ttime;

	struct cfqg_stats stats;

	struct cfqg_stats stats;	/* stats for this cfqg */

	struct cfqg_stats dead_stats;	/* stats pushed from dead children */

};



struct cfq_io_cq {
@@ -709,6 +710,47 @@ static void cfqg_stats_reset(struct cfqg_stats *stats) 
#endif

}



/* @to += @from */

static void cfqg_stats_merge(struct cfqg_stats *to, struct cfqg_stats *from)

{

	/* queued stats shouldn't be cleared */

	blkg_rwstat_merge(&to->service_bytes, &from->service_bytes);

	blkg_rwstat_merge(&to->serviced, &from->serviced);

	blkg_rwstat_merge(&to->merged, &from->merged);

	blkg_rwstat_merge(&to->service_time, &from->service_time);

	blkg_rwstat_merge(&to->wait_time, &from->wait_time);

	blkg_stat_merge(&from->time, &from->time);

#ifdef CONFIG_DEBUG_BLK_CGROUP

	blkg_stat_merge(&to->unaccounted_time, &from->unaccounted_time);

	blkg_stat_merge(&to->avg_queue_size_sum, &from->avg_queue_size_sum);

	blkg_stat_merge(&to->avg_queue_size_samples, &from->avg_queue_size_samples);

	blkg_stat_merge(&to->dequeue, &from->dequeue);

	blkg_stat_merge(&to->group_wait_time, &from->group_wait_time);

	blkg_stat_merge(&to->idle_time, &from->idle_time);

	blkg_stat_merge(&to->empty_time, &from->empty_time);

#endif

}



/*

 * Transfer @cfqg's stats to its parent's dead_stats so that the ancestors'

 * recursive stats can still account for the amount used by this cfqg after

 * it's gone.

 */

static void cfqg_stats_xfer_dead(struct cfq_group *cfqg)

{

	struct cfq_group *parent = cfqg_parent(cfqg);



	lockdep_assert_held(cfqg_to_blkg(cfqg)->q->queue_lock);



	if (unlikely(!parent))

		return;



	cfqg_stats_merge(&parent->dead_stats, &cfqg->stats);

	cfqg_stats_merge(&parent->dead_stats, &cfqg->dead_stats);

	cfqg_stats_reset(&cfqg->stats);

	cfqg_stats_reset(&cfqg->dead_stats);

}



#else	/* CONFIG_CFQ_GROUP_IOSCHED */



static inline struct cfq_group *cfqg_parent(struct cfq_group *cfqg) { return NULL; }
@@ -1475,11 +1517,23 @@ static void cfq_pd_init(struct blkcg_gq *blkg) 
	cfqg->leaf_weight = blkg->blkcg->cfq_leaf_weight;

}



static void cfq_pd_offline(struct blkcg_gq *blkg)

{

	/*

	 * @blkg is going offline and will be ignored by

	 * blkg_[rw]stat_recursive_sum().  Transfer stats to the parent so

	 * that they don't get lost.  If IOs complete after this point, the

	 * stats for them will be lost.  Oh well...

	 */

	cfqg_stats_xfer_dead(blkg_to_cfqg(blkg));

}



static void cfq_pd_reset_stats(struct blkcg_gq *blkg)

{

	struct cfq_group *cfqg = blkg_to_cfqg(blkg);



	cfqg_stats_reset(&cfqg->stats);

	cfqg_stats_reset(&cfqg->dead_stats);

}



/*
@@ -4408,6 +4462,7 @@ static struct blkcg_policy blkcg_policy_cfq = { 
	.cftypes		= cfq_blkcg_files,



	.pd_init_fn		= cfq_pd_init,

	.pd_offline_fn		= cfq_pd_offline,

	.pd_reset_stats_fn	= cfq_pd_reset_stats,

};

#endif