Re: [PATCH RESEND] blk-throttle: dispatch more sync writes in block throttle layer

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Hi Tejun,

Could you please kindly review this patch or give some advice?

Thanks.
Jiufei Xue

On 2018/1/23 上午10:08, xuejiufei wrote:
> Cgroup writeback is supported since v4.2. But there exists a problem
> in the following case.
> 
> A cgroup may send both buffer and direct/sync IOs. The foreground
> thread will be stalled when periodic writeback IOs is flushed because
> the service queue in block throttle layer already has a plenty of
> writeback IOs, then foreground IOs should be enqueued with its FIFO
> policy. The current policy is dispatching 6 reads and 2 writes during
> each round, sync writes will be significantly delayed.
> 
> This patch adds another queue in block throttle. Now there are 3 queues
> in a service queue: read, sync write, async write, and we can dispatch
> more sync writes than aync writes.
> 
> Test:
> 1) setup a memcg and a blkcg with uplimit bandwidth 20m/s;
> 2) start a script writing 5G buffer to page cache and start to sync
> 3) start sync writes:
>     dd if=/dev/zero of=test bs=4k count=12800 oflag=direct conv=notrunc
> 
> Unpatched:
> 52428800 bytes (52 MB) copied, 307.065 s, 171 kB/s
> 
> Patched:
> 52428800 bytes (52 MB) copied, 13.8192 s, 3.8 MB/s
> 
> Signed-off-by: Jiufei Xue <jiufei.xjf@xxxxxxxxxxxxxxx>
> ---
>  block/blk-throttle.c | 195 ++++++++++++++++++++++++++++++++++-----------------
>  1 file changed, 129 insertions(+), 66 deletions(-)
> 
> diff --git a/block/blk-throttle.c b/block/blk-throttle.c
> index d19f416..842257e 100644
> --- a/block/blk-throttle.c
> +++ b/block/blk-throttle.c
> @@ -14,10 +14,10 @@
>  #include "blk.h"
>  
>  /* Max dispatch from a group in 1 round */
> -static int throtl_grp_quantum = 8;
> +static int throtl_grp_quantum = 32;
>  
>  /* Total max dispatch from all groups in one round */
> -static int throtl_quantum = 32;
> +static int throtl_quantum = 128;
>  
>  /* Throttling is performed over a slice and after that slice is renewed */
>  #define DFL_THROTL_SLICE_HD (HZ / 10)
> @@ -43,6 +43,12 @@
>  /* A workqueue to queue throttle related work */
>  static struct workqueue_struct *kthrotld_workqueue;
>  
> +enum wl_type {
> +	READ_WORKLOAD = 0,
> +	SYNC_WRITE_WORKLOAD = 1,
> +	ASYNC_WRITE_WORKLOAD = 2
> +};
> +
>  /*
>   * To implement hierarchical throttling, throtl_grps form a tree and bios
>   * are dispatched upwards level by level until they reach the top and get
> @@ -79,8 +85,11 @@ struct throtl_service_queue {
>  	 * Bios queued directly to this service_queue or dispatched from
>  	 * children throtl_grp's.
>  	 */
> -	struct list_head	queued[2];	/* throtl_qnode [READ/WRITE] */
> -	unsigned int		nr_queued[2];	/* number of queued bios */
> +	/* throtl_qnode [READ/WRITE/ASYNC_WRITE] */
> +	struct list_head	queued[3];
> +
> +	unsigned int		nr_queued[3];	/* number of queued bios */
> +
>  
>  	/*
>  	 * RB tree of active children throtl_grp's, which are sorted by
> @@ -127,8 +136,8 @@ struct throtl_grp {
>  	 * with the sibling qnode_on_parents and the parent's
>  	 * qnode_on_self.
>  	 */
> -	struct throtl_qnode qnode_on_self[2];
> -	struct throtl_qnode qnode_on_parent[2];
> +	struct throtl_qnode qnode_on_self[3];
> +	struct throtl_qnode qnode_on_parent[3];
>  
>  	/*
>  	 * Dispatch time in jiffies. This is the estimated time when group
> @@ -202,7 +211,7 @@ struct throtl_data
>  	struct request_queue *queue;
>  
>  	/* Total Number of queued bios on READ and WRITE lists */
> -	unsigned int nr_queued[2];
> +	unsigned int nr_queued[3];
>  
>  	unsigned int throtl_slice;
>  
> @@ -274,6 +283,18 @@ static struct throtl_data *sq_to_td(struct throtl_service_queue *sq)
>  		return container_of(sq, struct throtl_data, service_queue);
>  }
>  
> +static inline enum wl_type bio_workload_type(struct bio *bio)
> +{
> +	return bio_data_dir(bio) ?
> +	       ((bio->bi_opf & REQ_SYNC) ? SYNC_WRITE_WORKLOAD :
> +	       ASYNC_WRITE_WORKLOAD) : READ_WORKLOAD;
> +}
> +
> +static inline bool wl_to_rw(enum wl_type type)
> +{
> +	return type >= SYNC_WRITE_WORKLOAD;
> +}
> +
>  /*
>   * cgroup's limit in LIMIT_MAX is scaled if low limit is set. This scale is to
>   * make the IO dispatch more smooth.
> @@ -475,8 +496,9 @@ static struct bio *throtl_pop_queued(struct list_head *queued,
>  /* init a service_queue, assumes the caller zeroed it */
>  static void throtl_service_queue_init(struct throtl_service_queue *sq)
>  {
> -	INIT_LIST_HEAD(&sq->queued[0]);
> -	INIT_LIST_HEAD(&sq->queued[1]);
> +	INIT_LIST_HEAD(&sq->queued[READ_WORKLOAD]);
> +	INIT_LIST_HEAD(&sq->queued[SYNC_WRITE_WORKLOAD]);
> +	INIT_LIST_HEAD(&sq->queued[ASYNC_WRITE_WORKLOAD]);
>  	sq->pending_tree = RB_ROOT;
>  	timer_setup(&sq->pending_timer, throtl_pending_timer_fn, 0);
>  }
> @@ -484,7 +506,7 @@ static void throtl_service_queue_init(struct throtl_service_queue *sq)
>  static struct blkg_policy_data *throtl_pd_alloc(gfp_t gfp, int node)
>  {
>  	struct throtl_grp *tg;
> -	int rw;
> +	enum wl_type type;
>  
>  	tg = kzalloc_node(sizeof(*tg), gfp, node);
>  	if (!tg)
> @@ -492,9 +514,9 @@ static struct blkg_policy_data *throtl_pd_alloc(gfp_t gfp, int node)
>  
>  	throtl_service_queue_init(&tg->service_queue);
>  
> -	for (rw = READ; rw <= WRITE; rw++) {
> -		throtl_qnode_init(&tg->qnode_on_self[rw], tg);
> -		throtl_qnode_init(&tg->qnode_on_parent[rw], tg);
> +	for (type = READ_WORKLOAD; type <= ASYNC_WRITE_WORKLOAD; type++) {
> +		throtl_qnode_init(&tg->qnode_on_self[type], tg);
> +		throtl_qnode_init(&tg->qnode_on_parent[type], tg);
>  	}
>  
>  	RB_CLEAR_NODE(&tg->rb_node);
> @@ -985,6 +1007,7 @@ static bool tg_may_dispatch(struct throtl_grp *tg, struct bio *bio,
>  			    unsigned long *wait)
>  {
>  	bool rw = bio_data_dir(bio);
> +	enum wl_type type = bio_workload_type(bio);
>  	unsigned long bps_wait = 0, iops_wait = 0, max_wait = 0;
>  
>  	/*
> @@ -993,8 +1016,8 @@ static bool tg_may_dispatch(struct throtl_grp *tg, struct bio *bio,
>  	 * this function with a different bio if there are other bios
>  	 * queued.
>  	 */
> -	BUG_ON(tg->service_queue.nr_queued[rw] &&
> -	       bio != throtl_peek_queued(&tg->service_queue.queued[rw]));
> +	BUG_ON(tg->service_queue.nr_queued[type] &&
> +	       bio != throtl_peek_queued(&tg->service_queue.queued[type]));
>  
>  	/* If tg->bps = -1, then BW is unlimited */
>  	if (tg_bps_limit(tg, rw) == U64_MAX &&
> @@ -1011,7 +1034,12 @@ static bool tg_may_dispatch(struct throtl_grp *tg, struct bio *bio,
>  	 * If there is queued bio, that means there should be an active
>  	 * slice and it should be extended instead.
>  	 */
> -	if (throtl_slice_used(tg, rw) && !(tg->service_queue.nr_queued[rw]))
> +	if (throtl_slice_used(tg, rw) &&
> +	   ((rw == READ &&
> +	    !tg->service_queue.nr_queued[READ_WORKLOAD]) ||
> +	    (rw == WRITE &&
> +	    !tg->service_queue.nr_queued[SYNC_WRITE_WORKLOAD] &&
> +	    !tg->service_queue.nr_queued[ASYNC_WRITE_WORKLOAD])))
>  		throtl_start_new_slice(tg, rw);
>  	else {
>  		if (time_before(tg->slice_end[rw],
> @@ -1072,10 +1100,10 @@ static void throtl_add_bio_tg(struct bio *bio, struct throtl_qnode *qn,
>  			      struct throtl_grp *tg)
>  {
>  	struct throtl_service_queue *sq = &tg->service_queue;
> -	bool rw = bio_data_dir(bio);
> +	int type = bio_workload_type(bio);
>  
>  	if (!qn)
> -		qn = &tg->qnode_on_self[rw];
> +		qn = &tg->qnode_on_self[type];
>  
>  	/*
>  	 * If @tg doesn't currently have any bios queued in the same
> @@ -1083,12 +1111,12 @@ static void throtl_add_bio_tg(struct bio *bio, struct throtl_qnode *qn,
>  	 * dispatched.  Mark that @tg was empty.  This is automatically
>  	 * cleaered on the next tg_update_disptime().
>  	 */
> -	if (!sq->nr_queued[rw])
> +	if (!sq->nr_queued[type])
>  		tg->flags |= THROTL_TG_WAS_EMPTY;
>  
> -	throtl_qnode_add_bio(bio, qn, &sq->queued[rw]);
> +	throtl_qnode_add_bio(bio, qn, &sq->queued[type]);
>  
> -	sq->nr_queued[rw]++;
> +	sq->nr_queued[type]++;
>  	throtl_enqueue_tg(tg);
>  }
>  
> @@ -1096,16 +1124,22 @@ static void tg_update_disptime(struct throtl_grp *tg)
>  {
>  	struct throtl_service_queue *sq = &tg->service_queue;
>  	unsigned long read_wait = -1, write_wait = -1, min_wait = -1, disptime;
> +	unsigned long sync_write_wait, async_write_wait;
>  	struct bio *bio;
>  
> -	bio = throtl_peek_queued(&sq->queued[READ]);
> +	bio = throtl_peek_queued(&sq->queued[READ_WORKLOAD]);
>  	if (bio)
>  		tg_may_dispatch(tg, bio, &read_wait);
>  
> -	bio = throtl_peek_queued(&sq->queued[WRITE]);
> +	bio = throtl_peek_queued(&sq->queued[SYNC_WRITE_WORKLOAD]);
> +	if (bio)
> +		tg_may_dispatch(tg, bio, &sync_write_wait);
> +
> +	bio = throtl_peek_queued(&sq->queued[ASYNC_WRITE_WORKLOAD]);
>  	if (bio)
> -		tg_may_dispatch(tg, bio, &write_wait);
> +		tg_may_dispatch(tg, bio, &async_write_wait);
>  
> +	write_wait = min(sync_write_wait, async_write_wait);
>  	min_wait = min(read_wait, write_wait);
>  	disptime = jiffies + min_wait;
>  
> @@ -1125,16 +1159,16 @@ static void start_parent_slice_with_credit(struct throtl_grp *child_tg,
>  		throtl_start_new_slice_with_credit(parent_tg, rw,
>  				child_tg->slice_start[rw]);
>  	}
> -
>  }
>  
> -static void tg_dispatch_one_bio(struct throtl_grp *tg, bool rw)
> +static void tg_dispatch_one_bio(struct throtl_grp *tg, enum wl_type type)
>  {
>  	struct throtl_service_queue *sq = &tg->service_queue;
>  	struct throtl_service_queue *parent_sq = sq->parent_sq;
>  	struct throtl_grp *parent_tg = sq_to_tg(parent_sq);
>  	struct throtl_grp *tg_to_put = NULL;
>  	struct bio *bio;
> +	bool rw = wl_to_rw(type);
>  
>  	/*
>  	 * @bio is being transferred from @tg to @parent_sq.  Popping a bio
> @@ -1142,8 +1176,8 @@ static void tg_dispatch_one_bio(struct throtl_grp *tg, bool rw)
>  	 * getting released prematurely.  Remember the tg to put and put it
>  	 * after @bio is transferred to @parent_sq.
>  	 */
> -	bio = throtl_pop_queued(&sq->queued[rw], &tg_to_put);
> -	sq->nr_queued[rw]--;
> +	bio = throtl_pop_queued(&sq->queued[type], &tg_to_put);
> +	sq->nr_queued[type]--;
>  
>  	throtl_charge_bio(tg, bio);
>  
> @@ -1155,13 +1189,13 @@ static void tg_dispatch_one_bio(struct throtl_grp *tg, bool rw)
>  	 * responsible for issuing these bios.
>  	 */
>  	if (parent_tg) {
> -		throtl_add_bio_tg(bio, &tg->qnode_on_parent[rw], parent_tg);
> +		throtl_add_bio_tg(bio, &tg->qnode_on_parent[type], parent_tg);
>  		start_parent_slice_with_credit(tg, parent_tg, rw);
>  	} else {
> -		throtl_qnode_add_bio(bio, &tg->qnode_on_parent[rw],
> -				     &parent_sq->queued[rw]);
> -		BUG_ON(tg->td->nr_queued[rw] <= 0);
> -		tg->td->nr_queued[rw]--;
> +		throtl_qnode_add_bio(bio, &tg->qnode_on_parent[type],
> +				     &parent_sq->queued[type]);
> +		BUG_ON(tg->td->nr_queued[type] <= 0);
> +		tg->td->nr_queued[type]--;
>  	}
>  
>  	throtl_trim_slice(tg, rw);
> @@ -1173,34 +1207,45 @@ static void tg_dispatch_one_bio(struct throtl_grp *tg, bool rw)
>  static int throtl_dispatch_tg(struct throtl_grp *tg)
>  {
>  	struct throtl_service_queue *sq = &tg->service_queue;
> -	unsigned int nr_reads = 0, nr_writes = 0;
> +	unsigned int nr_reads = 0, nr_async_writes = 0, nr_sync_writes = 0;
>  	unsigned int max_nr_reads = throtl_grp_quantum*3/4;
> -	unsigned int max_nr_writes = throtl_grp_quantum - max_nr_reads;
> +	unsigned int max_sync_writes = (throtl_grp_quantum - max_nr_reads)*7/8;
> +	unsigned int max_async_writes = throtl_grp_quantum - max_nr_reads
> +					- max_sync_writes;
>  	struct bio *bio;
>  
>  	/* Try to dispatch 75% READS and 25% WRITES */
> -
> -	while ((bio = throtl_peek_queued(&sq->queued[READ])) &&
> +	while ((bio = throtl_peek_queued(&sq->queued[READ_WORKLOAD])) &&
>  	       tg_may_dispatch(tg, bio, NULL)) {
>  
> -		tg_dispatch_one_bio(tg, bio_data_dir(bio));
> +		tg_dispatch_one_bio(tg, READ_WORKLOAD);
>  		nr_reads++;
>  
>  		if (nr_reads >= max_nr_reads)
>  			break;
>  	}
>  
> -	while ((bio = throtl_peek_queued(&sq->queued[WRITE])) &&
> +	while ((bio = throtl_peek_queued(&sq->queued[SYNC_WRITE_WORKLOAD])) &&
>  	       tg_may_dispatch(tg, bio, NULL)) {
>  
> -		tg_dispatch_one_bio(tg, bio_data_dir(bio));
> -		nr_writes++;
> +		tg_dispatch_one_bio(tg, SYNC_WRITE_WORKLOAD);
> +		nr_sync_writes++;
>  
> -		if (nr_writes >= max_nr_writes)
> +		if (nr_sync_writes >= max_sync_writes)
>  			break;
>  	}
>  
> -	return nr_reads + nr_writes;
> +	while ((bio = throtl_peek_queued(&sq->queued[ASYNC_WRITE_WORKLOAD])) &&
> +	       tg_may_dispatch(tg, bio, NULL)) {
> +
> +		tg_dispatch_one_bio(tg, ASYNC_WRITE_WORKLOAD);
> +		nr_async_writes++;
> +
> +		if (nr_async_writes >= max_async_writes)
> +			break;
> +	}
> +
> +	return nr_reads + nr_sync_writes + nr_async_writes;
>  }
>  
>  static int throtl_select_dispatch(struct throtl_service_queue *parent_sq)
> @@ -1221,7 +1266,9 @@ static int throtl_select_dispatch(struct throtl_service_queue *parent_sq)
>  
>  		nr_disp += throtl_dispatch_tg(tg);
>  
> -		if (sq->nr_queued[0] || sq->nr_queued[1])
> +		if (sq->nr_queued[READ_WORKLOAD] ||
> +		    sq->nr_queued[SYNC_WRITE_WORKLOAD] ||
> +		    sq->nr_queued[ASYNC_WRITE_WORKLOAD])
>  			tg_update_disptime(tg);
>  
>  		if (nr_disp >= throtl_quantum)
> @@ -1267,9 +1314,14 @@ static void throtl_pending_timer_fn(struct timer_list *t)
>  	dispatched = false;
>  
>  	while (true) {
> -		throtl_log(sq, "dispatch nr_queued=%u read=%u write=%u",
> -			   sq->nr_queued[READ] + sq->nr_queued[WRITE],
> -			   sq->nr_queued[READ], sq->nr_queued[WRITE]);
> +		throtl_log(sq,
> +			  "dispatch nr_queued=%u read=%u sync_write=%u async_write=%u",
> +			   sq->nr_queued[READ_WORKLOAD] +
> +			   sq->nr_queued[SYNC_WRITE_WORKLOAD] +
> +			   sq->nr_queued[ASYNC_WRITE_WORKLOAD],
> +			   sq->nr_queued[READ_WORKLOAD],
> +			   sq->nr_queued[SYNC_WRITE_WORKLOAD],
> +			   sq->nr_queued[ASYNC_WRITE_WORKLOAD]);
>  
>  		ret = throtl_select_dispatch(sq);
>  		if (ret) {
> @@ -1325,13 +1377,13 @@ static void blk_throtl_dispatch_work_fn(struct work_struct *work)
>  	struct bio_list bio_list_on_stack;
>  	struct bio *bio;
>  	struct blk_plug plug;
> -	int rw;
> +	enum wl_type type;
>  
>  	bio_list_init(&bio_list_on_stack);
>  
>  	spin_lock_irq(q->queue_lock);
> -	for (rw = READ; rw <= WRITE; rw++)
> -		while ((bio = throtl_pop_queued(&td_sq->queued[rw], NULL)))
> +	for (type = READ_WORKLOAD; type <= ASYNC_WRITE_WORKLOAD; type++)
> +		while ((bio = throtl_pop_queued(&td_sq->queued[type], NULL)))
>  			bio_list_add(&bio_list_on_stack, bio);
>  	spin_unlock_irq(q->queue_lock);
>  
> @@ -1820,11 +1872,13 @@ static bool throtl_tg_can_upgrade(struct throtl_grp *tg)
>  	write_limit = tg->bps[WRITE][LIMIT_LOW] || tg->iops[WRITE][LIMIT_LOW];
>  	if (!read_limit && !write_limit)
>  		return true;
> -	if (read_limit && sq->nr_queued[READ] &&
> -	    (!write_limit || sq->nr_queued[WRITE]))
> +	if (read_limit && sq->nr_queued[READ_WORKLOAD] &&
> +	    (!write_limit || sq->nr_queued[SYNC_WRITE_WORKLOAD] ||
> +			     sq->nr_queued[ASYNC_WRITE_WORKLOAD]))
>  		return true;
> -	if (write_limit && sq->nr_queued[WRITE] &&
> -	    (!read_limit || sq->nr_queued[READ]))
> +	if (write_limit && (sq->nr_queued[SYNC_WRITE_WORKLOAD] ||
> +			    sq->nr_queued[ASYNC_WRITE_WORKLOAD]) &&
> +	    (!read_limit || sq->nr_queued[READ_WORKLOAD]))
>  		return true;
>  
>  	if (time_after_eq(jiffies,
> @@ -2129,6 +2183,7 @@ bool blk_throtl_bio(struct request_queue *q, struct blkcg_gq *blkg,
>  	struct throtl_grp *tg = blkg_to_tg(blkg ?: q->root_blkg);
>  	struct throtl_service_queue *sq;
>  	bool rw = bio_data_dir(bio);
> +	enum wl_type type = bio_workload_type(bio);
>  	bool throttled = false;
>  	struct throtl_data *td = tg->td;
>  
> @@ -2157,7 +2212,7 @@ bool blk_throtl_bio(struct request_queue *q, struct blkcg_gq *blkg,
>  		throtl_downgrade_check(tg);
>  		throtl_upgrade_check(tg);
>  		/* throtl is FIFO - if bios are already queued, should queue */
> -		if (sq->nr_queued[rw])
> +		if (sq->nr_queued[type])
>  			break;
>  
>  		/* if above limits, break to queue */
> @@ -2191,7 +2246,7 @@ bool blk_throtl_bio(struct request_queue *q, struct blkcg_gq *blkg,
>  		 * Climb up the ladder.  If we''re already at the top, it
>  		 * can be executed directly.
>  		 */
> -		qn = &tg->qnode_on_parent[rw];
> +		qn = &tg->qnode_on_parent[type];
>  		sq = sq->parent_sq;
>  		tg = sq_to_tg(sq);
>  		if (!tg)
> @@ -2199,16 +2254,19 @@ bool blk_throtl_bio(struct request_queue *q, struct blkcg_gq *blkg,
>  	}
>  
>  	/* out-of-limit, queue to @tg */
> -	throtl_log(sq, "[%c] bio. bdisp=%llu sz=%u bps=%llu iodisp=%u iops=%u queued=%d/%d",
> +	throtl_log(sq, "[%c] bio. bdisp=%llu sz=%u bps=%llu iodisp=%u "
> +		   "iops=%u queued=%d/%d/%d",
>  		   rw == READ ? 'R' : 'W',
>  		   tg->bytes_disp[rw], bio->bi_iter.bi_size,
>  		   tg_bps_limit(tg, rw),
>  		   tg->io_disp[rw], tg_iops_limit(tg, rw),
> -		   sq->nr_queued[READ], sq->nr_queued[WRITE]);
> +		   sq->nr_queued[READ_WORKLOAD],
> +		   sq->nr_queued[SYNC_WRITE_WORKLOAD],
> +		   sq->nr_queued[ASYNC_WRITE_WORKLOAD]);
>  
>  	tg->last_low_overflow_time[rw] = jiffies;
>  
> -	td->nr_queued[rw]++;
> +	td->nr_queued[type]++;
>  	throtl_add_bio_tg(bio, qn, tg);
>  	throttled = true;
>  
> @@ -2334,10 +2392,15 @@ static void tg_drain_bios(struct throtl_service_queue *parent_sq)
>  
>  		throtl_dequeue_tg(tg);
>  
> -		while ((bio = throtl_peek_queued(&sq->queued[READ])))
> -			tg_dispatch_one_bio(tg, bio_data_dir(bio));
> -		while ((bio = throtl_peek_queued(&sq->queued[WRITE])))
> -			tg_dispatch_one_bio(tg, bio_data_dir(bio));
> +		while ((bio =
> +		      throtl_peek_queued(&sq->queued[READ_WORKLOAD])))
> +			tg_dispatch_one_bio(tg, READ_WORKLOAD);
> +		while ((bio =
> +		      throtl_peek_queued(&sq->queued[SYNC_WRITE_WORKLOAD])))
> +			tg_dispatch_one_bio(tg, SYNC_WRITE_WORKLOAD);
> +		while ((bio =
> +		      throtl_peek_queued(&sq->queued[ASYNC_WRITE_WORKLOAD])))
> +			tg_dispatch_one_bio(tg, ASYNC_WRITE_WORKLOAD);
>  	}
>  }
>  
> @@ -2354,7 +2417,7 @@ void blk_throtl_drain(struct request_queue *q)
>  	struct blkcg_gq *blkg;
>  	struct cgroup_subsys_state *pos_css;
>  	struct bio *bio;
> -	int rw;
> +	enum wl_type type;
>  
>  	queue_lockdep_assert_held(q);
>  	rcu_read_lock();
> @@ -2375,8 +2438,8 @@ void blk_throtl_drain(struct request_queue *q)
>  	spin_unlock_irq(q->queue_lock);
>  
>  	/* all bios now should be in td->service_queue, issue them */
> -	for (rw = READ; rw <= WRITE; rw++)
> -		while ((bio = throtl_pop_queued(&td->service_queue.queued[rw],
> +	for (type = READ_WORKLOAD; type <= ASYNC_WRITE_WORKLOAD; type++)
> +		while ((bio = throtl_pop_queued(&td->service_queue.queued[type],
>  						NULL)))
>  			generic_make_request(bio);
>  
> 
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