Re: [PATCH 18/19] io-controller: Debug hierarchical IO scheduling

[Gui Jianfeng <guijianfeng@cn.fujitsu.com>]

Vivek Goyal wrote:
> o Littile debugging aid for hierarchical IO scheduling.
> 
> o Enabled under CONFIG_DEBUG_GROUP_IOSCHED
> 
> o Currently it outputs more debug messages in blktrace output which helps
>   a great deal in debugging in hierarchical setup. It also creates additional
>   cgroup interfaces io.disk_queue and io.disk_dequeue to output some more
>   debugging data.
> 
> Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
> ---
>  block/Kconfig.iosched |   10 ++-
>  block/as-iosched.c    |   50 ++++++---
>  block/elevator-fq.c   |  285 ++++++++++++++++++++++++++++++++++++++++++++++++-
>  block/elevator-fq.h   |   26 +++++
>  4 files changed, 347 insertions(+), 24 deletions(-)
> 
> diff --git a/block/Kconfig.iosched b/block/Kconfig.iosched
> index 0677099..79f188c 100644
> --- a/block/Kconfig.iosched
> +++ b/block/Kconfig.iosched
> @@ -140,6 +140,14 @@ config TRACK_ASYNC_CONTEXT
>  	  request, original owner of the bio is decided by using io tracking
>  	  patches otherwise we continue to attribute the request to the
>  	  submitting thread.
> -endmenu
>  
> +config DEBUG_GROUP_IOSCHED
> +	bool "Debug Hierarchical Scheduling support"
> +	depends on CGROUPS && GROUP_IOSCHED
> +	default n
> +	---help---
> +	  Enable some debugging hooks for hierarchical scheduling support.
> +	  Currently it just outputs more information in blktrace output.
> +
> +endmenu
>  endif
> diff --git a/block/as-iosched.c b/block/as-iosched.c
> index b0c66e4..735d055 100644
> --- a/block/as-iosched.c
> +++ b/block/as-iosched.c
> @@ -78,6 +78,7 @@ enum anticipation_status {
>  };
>  
>  struct as_queue {
> +	struct io_queue *ioq;
>  	/*
>  	 * requests (as_rq s) are present on both sort_list and fifo_list
>  	 */
> @@ -162,6 +163,17 @@ enum arq_state {
>  #define RQ_STATE(rq)	((enum arq_state)(rq)->elevator_private2)
>  #define RQ_SET_STATE(rq, state)	((rq)->elevator_private2 = (void *) state)
>  
> +#ifdef CONFIG_DEBUG_GROUP_IOSCHED
> +#define as_log_asq(ad, asq, fmt, args...)				\
> +{									\
> +	blk_add_trace_msg((ad)->q, "as %s " fmt,			\
> +			ioq_to_io_group((asq)->ioq)->path, ##args);	\
> +}
> +#else
> +#define as_log_asq(ad, asq, fmt, args...) \
> +	blk_add_trace_msg((ad)->q, "as " fmt, ##args)
> +#endif
> +
>  #define as_log(ad, fmt, args...)        \
>  	blk_add_trace_msg((ad)->q, "as " fmt, ##args)
>  
> @@ -225,7 +237,7 @@ static void as_save_batch_context(struct as_data *ad, struct as_queue *asq)
>  	}
>  
>  out:
> -	as_log(ad, "save batch: dir=%c time_left=%d changed_batch=%d"
> +	as_log_asq(ad, asq, "save batch: dir=%c time_left=%d changed_batch=%d"
>  			" new_batch=%d, antic_status=%d",
>  			ad->batch_data_dir ? 'R' : 'W',
>  			asq->current_batch_time_left,
> @@ -247,8 +259,8 @@ static void as_restore_batch_context(struct as_data *ad, struct as_queue *asq)
>  						asq->current_batch_time_left;
>  	/* restore asq batch_data_dir info */
>  	ad->batch_data_dir = asq->saved_batch_data_dir;
> -	as_log(ad, "restore batch: dir=%c time=%d reads_q=%d writes_q=%d"
> -			" ad->antic_status=%d",
> +	as_log_asq(ad, asq, "restore batch: dir=%c time=%d reads_q=%d"
> +			" writes_q=%d ad->antic_status=%d",
>  			ad->batch_data_dir ? 'R' : 'W',
>  			asq->current_batch_time_left,
>  			asq->nr_queued[1], asq->nr_queued[0],
> @@ -277,8 +289,8 @@ static int as_expire_ioq(struct request_queue *q, void *sched_queue,
>  	int status = ad->antic_status;
>  	struct as_queue *asq = sched_queue;
>  
> -	as_log(ad, "as_expire_ioq slice_expired=%d, force=%d", slice_expired,
> -		force);
> +	as_log_asq(ad, asq, "as_expire_ioq slice_expired=%d, force=%d",
> +			slice_expired, force);
>  
>  	/* Forced expiry. We don't have a choice */
>  	if (force) {
> @@ -1019,9 +1031,10 @@ static void update_write_batch(struct as_data *ad, struct request *rq)
>  	if (write_time < 0)
>  		write_time = 0;
>  
> -	as_log(ad, "upd write: write_time=%d batch=%d write_batch_idled=%d"
> -			" current_write_count=%d", write_time, batch,
> -			asq->write_batch_idled, asq->current_write_count);
> +	as_log_asq(ad, asq, "upd write: write_time=%d batch=%d"
> +			" write_batch_idled=%d current_write_count=%d",
> +			write_time, batch, asq->write_batch_idled,
> +			asq->current_write_count);
>  
>  	if (write_time > batch && !asq->write_batch_idled) {
>  		if (write_time > batch * 3)
> @@ -1038,7 +1051,7 @@ static void update_write_batch(struct as_data *ad, struct request *rq)
>  	if (asq->write_batch_count < 1)
>  		asq->write_batch_count = 1;
>  
> -	as_log(ad, "upd write count=%d", asq->write_batch_count);
> +	as_log_asq(ad, asq, "upd write count=%d", asq->write_batch_count);
>  }
>  
>  /*
> @@ -1057,7 +1070,7 @@ static void as_completed_request(struct request_queue *q, struct request *rq)
>  		goto out;
>  	}
>  
> -	as_log(ad, "complete: reads_q=%d writes_q=%d changed_batch=%d"
> +	as_log_asq(ad, asq, "complete: reads_q=%d writes_q=%d changed_batch=%d"
>  		" new_batch=%d switch_queue=%d, dir=%c",
>  		asq->nr_queued[1], asq->nr_queued[0], ad->changed_batch,
>  		ad->new_batch, ad->switch_queue,
> @@ -1251,7 +1264,7 @@ static void as_move_to_dispatch(struct as_data *ad, struct request *rq)
>  	if (RQ_IOC(rq) && RQ_IOC(rq)->aic)
>  		atomic_inc(&RQ_IOC(rq)->aic->nr_dispatched);
>  	ad->nr_dispatched++;
> -	as_log(ad, "dispatch req dir=%c nr_dispatched = %d",
> +	as_log_asq(ad, asq, "dispatch req dir=%c nr_dispatched = %d",
>  			data_dir ? 'R' : 'W', ad->nr_dispatched);
>  }
>  
> @@ -1300,7 +1313,7 @@ static int as_dispatch_request(struct request_queue *q, int force)
>  		}
>  		asq->last_check_fifo[BLK_RW_ASYNC] = jiffies;
>  
> -		as_log(ad, "forced dispatch");
> +		as_log_asq(ad, asq, "forced dispatch");
>  		return dispatched;
>  	}
>  
> @@ -1314,7 +1327,7 @@ static int as_dispatch_request(struct request_queue *q, int force)
>  		|| ad->antic_status == ANTIC_WAIT_REQ
>  		|| ad->antic_status == ANTIC_WAIT_NEXT
>  		|| ad->changed_batch) {
> -		as_log(ad, "no dispatch. read_q=%d, writes_q=%d"
> +		as_log_asq(ad, asq, "no dispatch. read_q=%d, writes_q=%d"
>  			" ad->antic_status=%d, changed_batch=%d,"
>  			" switch_queue=%d new_batch=%d", asq->nr_queued[1],
>  			asq->nr_queued[0], ad->antic_status, ad->changed_batch,
> @@ -1333,7 +1346,7 @@ static int as_dispatch_request(struct request_queue *q, int force)
>  				goto fifo_expired;
>  
>  			if (as_can_anticipate(ad, rq)) {
> -				as_log(ad, "can_anticipate = 1");
> +				as_log_asq(ad, asq, "can_anticipate = 1");
>  				as_antic_waitreq(ad);
>  				return 0;
>  			}
> @@ -1353,7 +1366,7 @@ static int as_dispatch_request(struct request_queue *q, int force)
>  	 * data direction (read / write)
>  	 */
>  
> -	as_log(ad, "select a fresh batch and request");
> +	as_log_asq(ad, asq, "select a fresh batch and request");
>  
>  	if (reads) {
>  		BUG_ON(RB_EMPTY_ROOT(&asq->sort_list[BLK_RW_SYNC]));
> @@ -1369,7 +1382,7 @@ static int as_dispatch_request(struct request_queue *q, int force)
>  			ad->changed_batch = 1;
>  		}
>  		ad->batch_data_dir = BLK_RW_SYNC;
> -		as_log(ad, "new batch dir is sync");
> +		as_log_asq(ad, asq, "new batch dir is sync");
>  		rq = rq_entry_fifo(asq->fifo_list[BLK_RW_SYNC].next);
>  		asq->last_check_fifo[ad->batch_data_dir] = jiffies;
>  		goto dispatch_request;
> @@ -1394,7 +1407,7 @@ dispatch_writes:
>  			ad->new_batch = 0;
>  		}
>  		ad->batch_data_dir = BLK_RW_ASYNC;
> -		as_log(ad, "new batch dir is async");
> +		as_log_asq(ad, asq, "new batch dir is async");
>  		asq->current_write_count = asq->write_batch_count;
>  		asq->write_batch_idled = 0;
>  		rq = rq_entry_fifo(asq->fifo_list[BLK_RW_ASYNC].next);
> @@ -1457,7 +1470,7 @@ static void as_add_request(struct request_queue *q, struct request *rq)
>  	rq->elevator_private = as_get_io_context(q->node);
>  
>  	asq->nr_queued[data_dir]++;
> -	as_log(ad, "add a %c request read_q=%d write_q=%d",
> +	as_log_asq(ad, asq, "add a %c request read_q=%d write_q=%d",
>  			data_dir ? 'R' : 'W', asq->nr_queued[1],
>  			asq->nr_queued[0]);
>  
> @@ -1616,6 +1629,7 @@ static void *as_alloc_as_queue(struct request_queue *q,
>  
>  	if (asq->write_batch_count < 2)
>  		asq->write_batch_count = 2;
> +	asq->ioq = ioq;
>  out:
>  	return asq;
>  }
> diff --git a/block/elevator-fq.c b/block/elevator-fq.c
> index 207664d..207bdf1 100644
> --- a/block/elevator-fq.c
> +++ b/block/elevator-fq.c
> @@ -117,6 +117,126 @@ static inline int iog_deleting(struct io_group *iog)
>  	return iog->deleting;
>  }
>  
> +static inline struct io_group *io_entity_to_iog(struct io_entity *entity)
> +{
> +	struct io_group *iog = NULL;
> +
> +	BUG_ON(entity == NULL);
> +	if (entity->my_sched_data != NULL)
> +		iog = container_of(entity, struct io_group, entity);
> +	return iog;
> +}
> +
> +/* Returns parent group of io group */
> +static inline struct io_group *iog_parent(struct io_group *iog)
> +{
> +	struct io_group *piog;
> +
> +	if (!iog->entity.sched_data)
> +		return NULL;
> +
> +	/*
> +	 * Not following entity->parent pointer as for top level groups
> +	 * this pointer is NULL.
> +	 */
> +	piog = container_of(iog->entity.sched_data, struct io_group,
> +					sched_data);
> +	return piog;
> +}
> +
> +#ifdef CONFIG_DEBUG_GROUP_IOSCHED
> +static void io_group_path(struct io_group *iog, char *buf, int buflen)
> +{
> +	unsigned short id = iog->iocg_id;
> +	struct cgroup_subsys_state *css;
> +
> +	rcu_read_lock();
> +
> +	if (!id)
> +		goto out;
> +
> +	css = css_lookup(&io_subsys, id);
> +	if (!css)
> +		goto out;
> +
> +	if (!css_tryget(css))
> +		goto out;
> +
> +	cgroup_path(css->cgroup, buf, buflen);
> +
> +	css_put(css);
> +
> +	rcu_read_unlock();
> +	return;
> +out:
> +	rcu_read_unlock();
> +	buf[0] = '\0';
> +	return;
> +}
> +
> +/*
> + * An entity has been freshly added to active tree. Either it came from
> + * idle tree or it was not on any of the trees. Do the accounting.
> + */
> +static inline void bfq_account_for_entity_addition(struct io_entity *entity)
> +{
> +	struct io_group *iog = io_entity_to_iog(entity);
> +
> +	if (iog) {
> +		struct elv_fq_data *efqd;
> +		char path[128];
> +
> +		/*
> +		 * Keep track of how many times a group has been removed
> +		 * from active tree because it did not have any active
> +		 * backlogged ioq under it
> +		 */

Hi Vivek,

Should the comment here be "added to" rather than "removed from"?

> +		iog->queue++;
> +		iog->queue_start = jiffies;
> +
> +		/* Log group addition event */
> +		rcu_read_lock();
> +		efqd = rcu_dereference(iog->key);
> +		if (efqd) {
> +			io_group_path(iog, path, sizeof(path));
> +			elv_log(efqd, "add group=%s weight=%ld", path,
> +					iog->entity.weight);
> +		}
> +		rcu_read_unlock();
> +	}
> +}
> +
> +/*
> + * An entity got removed from active tree and either went to idle tree or
> + * not is on any of the tree. Do the accouting
> + */
> +static inline void bfq_account_for_entity_deletion(struct io_entity *entity)
> +{
> +	struct io_group *iog = io_entity_to_iog(entity);
> +
> +	if (iog) {
> +		struct elv_fq_data *efqd;
> +		char path[128];
> +
> +		iog->dequeue++;
> +		/* Keep a track of how long group was on active tree */
> +		iog->queue_duration += jiffies_to_msecs(jiffies -
> +						iog->queue_start);
> +		iog->queue_start = 0;
> +
> +		/* Log group deletion event */
> +		rcu_read_lock();
> +		efqd = rcu_dereference(iog->key);
> +		if (efqd) {
> +			io_group_path(iog, path, sizeof(path));
> +			elv_log(efqd, "del group=%s weight=%ld", path,
> +					iog->entity.weight);
> +		}
> +		rcu_read_unlock();
> +	}
> +}
> +#endif
> +
>  #else /* GROUP_IOSCHED */
>  #define for_each_entity(entity)	\
>  	for (; entity != NULL; entity = NULL)
> @@ -139,6 +259,12 @@ static inline int iog_deleting(struct io_group *iog)
>  	/* In flat mode, root cgroup can't be deleted. */
>  	return 0;
>  }
> +
> +static inline struct io_group *io_entity_to_iog(struct io_entity *entity)
> +{
> +	return NULL;
> +}
> +
>  #endif
>  
>  /*
> @@ -572,6 +698,7 @@ static void __bfq_activate_entity(struct io_entity *entity, int add_front)
>  {
>  	struct io_sched_data *sd = entity->sched_data;
>  	struct io_service_tree *st = io_entity_service_tree(entity);
> +	int newly_added = 0;
>  
>  	if (entity == sd->active_entity) {
>  		BUG_ON(entity->tree != NULL);
> @@ -598,6 +725,7 @@ static void __bfq_activate_entity(struct io_entity *entity, int add_front)
>  		bfq_idle_extract(st, entity);
>  		entity->start = bfq_gt(st->vtime, entity->finish) ?
>  				       st->vtime : entity->finish;
> +		newly_added = 1;
>  	} else {
>  		/*
>  		 * The finish time of the entity may be invalid, and
> @@ -610,6 +738,7 @@ static void __bfq_activate_entity(struct io_entity *entity, int add_front)
>  
>  		BUG_ON(entity->on_st);
>  		entity->on_st = 1;
> +		newly_added = 1;
>  	}
>  
>  	st = __bfq_entity_update_prio(st, entity);
> @@ -647,6 +776,10 @@ static void __bfq_activate_entity(struct io_entity *entity, int add_front)
>  		bfq_calc_finish(entity, entity->budget);
>  	}
>  	bfq_active_insert(st, entity);
> +#ifdef CONFIG_DEBUG_GROUP_IOSCHED
> +	if (newly_added)
> +		bfq_account_for_entity_addition(entity);
> +#endif
>  }
>  
>  /**
> @@ -717,6 +850,9 @@ int __bfq_deactivate_entity(struct io_entity *entity, int requeue)
>  	BUG_ON(sd->active_entity == entity);
>  	BUG_ON(sd->next_active == entity);
>  
> +#ifdef CONFIG_DEBUG_GROUP_IOSCHED
> +	bfq_account_for_entity_deletion(entity);
> +#endif
>  	return ret;
>  }
>  
> @@ -1209,6 +1345,67 @@ static int io_cgroup_disk_sectors_read(struct cgroup *cgroup,
>  	return 0;
>  }
>  
> +#ifdef CONFIG_DEBUG_GROUP_IOSCHED
> +static int io_cgroup_disk_queue_read(struct cgroup *cgroup,
> +			struct cftype *cftype, struct seq_file *m)
> +{
> +	struct io_cgroup *iocg = NULL;
> +	struct io_group *iog = NULL;
> +	struct hlist_node *n;
> +
> +	if (!cgroup_lock_live_group(cgroup))
> +		return -ENODEV;
> +
> +	iocg = cgroup_to_io_cgroup(cgroup);
> +	spin_lock_irq(&iocg->lock);
> +	/* Loop through all the io groups and print statistics */
> +	hlist_for_each_entry_rcu(iog, n, &iocg->group_data, group_node) {
> +		/*
> +		 * There might be groups which are not functional and
> +		 * waiting to be reclaimed upon cgoup deletion.
> +		 */
> +		if (iog->key) {
> +			seq_printf(m, "%u %u %lu %lu\n", MAJOR(iog->dev),
> +					MINOR(iog->dev), iog->queue,
> +					iog->queue_duration);
> +		}
> +	}
> +	spin_unlock_irq(&iocg->lock);
> +	cgroup_unlock();
> +
> +	return 0;
> +}
> +
> +static int io_cgroup_disk_dequeue_read(struct cgroup *cgroup,
> +			struct cftype *cftype, struct seq_file *m)
> +{
> +	struct io_cgroup *iocg = NULL;
> +	struct io_group *iog = NULL;
> +	struct hlist_node *n;
> +
> +	if (!cgroup_lock_live_group(cgroup))
> +		return -ENODEV;
> +
> +	iocg = cgroup_to_io_cgroup(cgroup);
> +	spin_lock_irq(&iocg->lock);
> +	/* Loop through all the io groups and print statistics */
> +	hlist_for_each_entry_rcu(iog, n, &iocg->group_data, group_node) {
> +		/*
> +		 * There might be groups which are not functional and
> +		 * waiting to be reclaimed upon cgoup deletion.
> +		 */
> +		if (iog->key) {
> +			seq_printf(m, "%u %u %lu\n", MAJOR(iog->dev),
> +					MINOR(iog->dev), iog->dequeue);
> +		}
> +	}
> +	spin_unlock_irq(&iocg->lock);
> +	cgroup_unlock();
> +
> +	return 0;
> +}
> +#endif
> +
>  /**
>   * bfq_group_chain_alloc - allocate a chain of groups.
>   * @bfqd: queue descriptor.
> @@ -1263,7 +1460,9 @@ struct io_group *io_group_chain_alloc(struct request_queue *q, void *key,
>  		}
>  
>  		blk_init_request_list(&iog->rl);
> -
> +#ifdef CONFIG_DEBUG_GROUP_IOSCHED
> +		io_group_path(iog, iog->path, sizeof(iog->path));
> +#endif
>  		if (leaf == NULL) {
>  			leaf = iog;
>  			prev = leaf;
> @@ -1766,6 +1965,16 @@ struct cftype bfqio_files[] = {
>  		.name = "disk_sectors",
>  		.read_seq_string = io_cgroup_disk_sectors_read,
>  	},
> +#ifdef CONFIG_DEBUG_GROUP_IOSCHED
> +	{
> +		.name = "disk_queue",
> +		.read_seq_string = io_cgroup_disk_queue_read,
> +	},
> +	{
> +		.name = "disk_dequeue",
> +		.read_seq_string = io_cgroup_disk_dequeue_read,
> +	},
> +#endif
>  };
>  
>  int iocg_populate(struct cgroup_subsys *subsys, struct cgroup *cgroup)
> @@ -2090,6 +2299,7 @@ struct cgroup_subsys io_subsys = {
>  	.destroy = iocg_destroy,
>  	.populate = iocg_populate,
>  	.subsys_id = io_subsys_id,
> +	.use_id = 1,
>  };
>  
>  /*
> @@ -2380,6 +2590,22 @@ EXPORT_SYMBOL(elv_get_slice_idle);
>  void elv_ioq_served(struct io_queue *ioq, bfq_service_t served)
>  {
>  	entity_served(&ioq->entity, served, ioq->nr_sectors);
> +
> +#ifdef CONFIG_DEBUG_GROUP_IOSCHED
> +		{
> +			struct elv_fq_data *efqd = ioq->efqd;
> +			struct io_group *iog = ioq_to_io_group(ioq);
> +			elv_log_ioq(efqd, ioq, "ioq served: QSt=0x%lx QSs=0x%lx"
> +				" QTt=0x%lx QTs=0x%lx GTt=0x%lx "
> +				" GTs=0x%lx rq_queued=%d",
> +				served, ioq->nr_sectors,
> +				ioq->entity.total_service,
> +				ioq->entity.total_sector_service,
> +				iog->entity.total_service,
> +				iog->entity.total_sector_service,
> +				ioq->nr_queued);
> +		}
> +#endif
>  }
>  
>  /* Tells whether ioq is queued in root group or not */
> @@ -2847,10 +3073,30 @@ static void __elv_set_active_ioq(struct elv_fq_data *efqd, struct io_queue *ioq,
>  	if (ioq) {
>  		struct io_group *iog = ioq_to_io_group(ioq);
>  		elv_log_ioq(efqd, ioq, "set_active, busy=%d ioprio=%d"
> -				" weight=%ld group_weight=%ld",
> +				" weight=%ld rq_queued=%d group_weight=%ld",
>  				efqd->busy_queues,
>  				ioq->entity.ioprio, ioq->entity.weight,
> -				iog_weight(iog));
> +				ioq->nr_queued, iog_weight(iog));
> +
> +#ifdef CONFIG_DEBUG_GROUP_IOSCHED
> +			{
> +				int nr_active = 0;
> +				struct io_group *parent = NULL;
> +
> +				parent = iog_parent(iog);
> +				if (parent)
> +					nr_active = elv_iog_nr_active(parent);
> +
> +				elv_log_ioq(efqd, ioq, "set_active, ioq"
> +				" nrgrps=%d QTt=0x%lx QTs=0x%lx GTt=0x%lx "
> +				" GTs=0x%lx rq_queued=%d", nr_active,
> +				ioq->entity.total_service,
> +				ioq->entity.total_sector_service,
> +				iog->entity.total_service,
> +				iog->entity.total_sector_service,
> +				ioq->nr_queued);
> +			}
> +#endif
>  		ioq->slice_end = 0;
>  
>  		elv_clear_ioq_wait_request(ioq);
> @@ -2927,12 +3173,26 @@ void elv_add_ioq_busy(struct elv_fq_data *efqd, struct io_queue *ioq)
>  {
>  	BUG_ON(elv_ioq_busy(ioq));
>  	BUG_ON(ioq == efqd->active_queue);
> -	elv_log_ioq(efqd, ioq, "add to busy");
>  	elv_activate_ioq(ioq, 0);
>  	elv_mark_ioq_busy(ioq);
>  	efqd->busy_queues++;
>  	if (elv_ioq_class_rt(ioq))
>  		efqd->busy_rt_queues++;
> +
> +#ifdef CONFIG_DEBUG_GROUP_IOSCHED
> +	{
> +		struct io_group *iog = ioq_to_io_group(ioq);
> +		elv_log_ioq(efqd, ioq, "add to busy: QTt=0x%lx QTs=0x%lx"
> +			" ioq grp=%s GTt=0x%lx GTs=0x%lx rq_queued=%d",
> +			ioq->entity.total_service,
> +			ioq->entity.total_sector_service,
> +			iog->entity.total_service,
> +			iog->entity.total_sector_service,
> +			ioq->nr_queued);
> +	}
> +#else
> +	elv_log_ioq(efqd, ioq, "add to busy");
> +#endif
>  }
>  
>  void elv_del_ioq_busy(struct elevator_queue *e, struct io_queue *ioq,
> @@ -2942,7 +3202,21 @@ void elv_del_ioq_busy(struct elevator_queue *e, struct io_queue *ioq,
>  
>  	BUG_ON(!elv_ioq_busy(ioq));
>  	BUG_ON(ioq->nr_queued);
> +#ifdef CONFIG_DEBUG_GROUP_IOSCHED
> +	{
> +		struct io_group *iog = ioq_to_io_group(ioq);
> +		elv_log_ioq(efqd, ioq, "del from busy: QTt=0x%lx "
> +			"QTs=0x%lx ioq GTt=0x%lx GTs=0x%lx "
> +			"rq_queued=%d",
> +			ioq->entity.total_service,
> +			ioq->entity.total_sector_service,
> +			iog->entity.total_service,
> +			iog->entity.total_sector_service,
> +			ioq->nr_queued);
> +	}
> +#else
>  	elv_log_ioq(efqd, ioq, "del from busy");
> +#endif
>  	elv_clear_ioq_busy(ioq);
>  	BUG_ON(efqd->busy_queues == 0);
>  	efqd->busy_queues--;
> @@ -3179,6 +3453,7 @@ void elv_ioq_request_add(struct request_queue *q, struct request *rq)
>  
>  	elv_ioq_update_io_thinktime(ioq);
>  	elv_ioq_update_idle_window(q->elevator, ioq, rq);
> +	elv_log_ioq(efqd, ioq, "add rq: rq_queued=%d", ioq->nr_queued);
>  
>  	if (ioq == elv_active_ioq(q->elevator)) {
>  		/*
> @@ -3412,7 +3687,7 @@ void *elv_fq_select_ioq(struct request_queue *q, int force)
>  	}
>  
>  	/* We are waiting for this queue to become busy before it expires.*/
> -	if (efqd->fairness && elv_ioq_wait_busy(ioq)) {
> +	if (elv_ioq_wait_busy(ioq)) {
>  		ioq = NULL;
>  		goto keep_queue;
>  	}
> diff --git a/block/elevator-fq.h b/block/elevator-fq.h
> index ff409ec..b5cff90 100644
> --- a/block/elevator-fq.h
> +++ b/block/elevator-fq.h
> @@ -251,6 +251,23 @@ struct io_group {
>  
>  	/* request list associated with the group */
>  	struct request_list rl;
> +
> +#ifdef CONFIG_DEBUG_GROUP_IOSCHED
> +	/* How many times this group has been added to active tree */
> +	unsigned long queue;
> +
> +	/* How long this group remained on active tree, in ms */
> +	unsigned long queue_duration;
> +
> +	/* When was this group added to active tree */
> +	unsigned long queue_start;
> +
> +	/* How many times this group has been removed from active tree */
> +	unsigned long dequeue;
> +
> +	/* Store cgroup path */
> +	char path[128];
> +#endif
>  };
>  
>  struct io_policy_node {
> @@ -353,9 +370,18 @@ extern int elv_slice_idle;
>  extern int elv_slice_async;
>  
>  /* Logging facilities. */
> +#ifdef CONFIG_DEBUG_GROUP_IOSCHED
> +#define elv_log_ioq(efqd, ioq, fmt, args...) \
> +{								\
> +	blk_add_trace_msg((efqd)->queue, "elv%d%c %s " fmt, (ioq)->pid,	\
> +			elv_ioq_sync(ioq) ? 'S' : 'A', \
> +			ioq_to_io_group(ioq)->path, ##args); \
> +}
> +#else
>  #define elv_log_ioq(efqd, ioq, fmt, args...) \
>  	blk_add_trace_msg((efqd)->queue, "elv%d%c " fmt, (ioq)->pid,	\
>  				elv_ioq_sync(ioq) ? 'S' : 'A', ##args)
> +#endif
>  
>  #define elv_log(efqd, fmt, args...) \
>  	blk_add_trace_msg((efqd)->queue, "elv " fmt, ##args)

-- 
Regards
Gui Jianfeng