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Subject[PATCH 18/24] io-controller: anticipatory changes for hierarchical fair queuing
Date
This patch changes anticipatory scheduler to use queue scheduling code from
elevator layer. One can go back to old as by deselecting
CONFIG_IOSCHED_AS_HIER. Even with CONFIG_IOSCHED_AS_HIER=y, with-out any
other cgroup created, AS behavior should remain the same as old.

o AS is a single queue ioschduler, that means there is one AS queue per group.

o common layer code select the queue to dispatch from based on fairness, and
then AS code selects the request with-in group.

o AS runs reads and writes batches with-in group. So common layer runs timed
group queues and with-in group time, AS runs timed batches of reads and
writes.

o Note: Previously AS write batch length was adjusted synamically whenever
a W->R batch data direction took place and when first request from the
read batch completed.

Now write batch updation takes place when last request from the write
batch has finished during W->R transition.

o AS runs its own anticipation logic to anticipate on reads. common layer also
does the anticipation on the group if think time of the group is with-in
slice_idle.

o Introduced few debugging messages in AS.

Signed-off-by: Nauman Rafique <nauman@google.com>
Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
---
block/Kconfig.iosched | 12 ++
block/as-iosched.c | 294 +++++++++++++++++++++++++++++++++++++++++++++-
block/elevator-fq.c | 93 +++++++++++++--
block/elevator-fq.h | 3 +
include/linux/elevator.h | 2 +
5 files changed, 386 insertions(+), 18 deletions(-)
diff --git a/block/Kconfig.iosched b/block/Kconfig.iosched
index cc87c87..8ab08da 100644
--- a/block/Kconfig.iosched
+++ b/block/Kconfig.iosched
@@ -45,6 +45,18 @@ config IOSCHED_AS
deadline I/O scheduler, it can also be slower in some cases
especially some database loads.

+config IOSCHED_AS_HIER
+ bool "Anticipatory Hierarchical Scheduling support"
+ depends on IOSCHED_AS && CGROUPS
+ select ELV_FAIR_QUEUING
+ select GROUP_IOSCHED
+ default n
+ ---help---
+ Enable hierarhical scheduling in anticipatory. In this mode
+ anticipatory keeps one IO queue per cgroup instead of a global
+ queue. Elevator fair queuing logic ensures fairness among various
+ queues.
+
config IOSCHED_DEADLINE
tristate "Deadline I/O scheduler"
default y
diff --git a/block/as-iosched.c b/block/as-iosched.c
index 6d2468b..2f68d5b 100644
--- a/block/as-iosched.c
+++ b/block/as-iosched.c
@@ -16,6 +16,7 @@
#include <linux/compiler.h>
#include <linux/rbtree.h>
#include <linux/interrupt.h>
+#include <linux/blktrace_api.h>

/*
* See Documentation/block/as-iosched.txt
@@ -77,6 +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
*/
@@ -84,10 +86,24 @@ struct as_queue {
struct list_head fifo_list[2];

struct request *next_rq[2]; /* next in sort order */
+
+ /*
+ * If an as_queue is switched while a batch is running, then we
+ * store the time left before current batch will expire
+ */
+ long current_batch_time_left;
+
+ /*
+ * batch data dir when queue was scheduled out. This will be used
+ * to setup ad->batch_data_dir when queue is scheduled in.
+ */
+ int saved_batch_data_dir;
+
unsigned long last_check_fifo[2];
int write_batch_count; /* max # of reqs in a write batch */
int current_write_count; /* how many requests left this batch */
int write_batch_idled; /* has the write batch gone idle? */
+ int nr_queued[2];
};

struct as_data {
@@ -123,6 +139,9 @@ struct as_data {
unsigned long fifo_expire[2];
unsigned long batch_expire[2];
unsigned long antic_expire;
+
+ /* elevator requested a queue switch. */
+ int switch_queue;
};

/*
@@ -144,12 +163,185 @@ 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)
+
static DEFINE_PER_CPU(unsigned long, ioc_count);
static struct completion *ioc_gone;
static DEFINE_SPINLOCK(ioc_gone_lock);

static void as_move_to_dispatch(struct as_data *ad, struct request *rq);
static void as_antic_stop(struct as_data *ad);
+static inline int as_batch_expired(struct as_data *ad, struct as_queue *asq);
+
+#ifdef CONFIG_IOSCHED_AS_HIER
+static void as_save_batch_context(struct as_data *ad, struct as_queue *asq)
+{
+ /* Save batch data dir */
+ asq->saved_batch_data_dir = ad->batch_data_dir;
+
+ if (ad->changed_batch) {
+ /*
+ * In case of force expire, we come here. Batch changeover
+ * has been signalled but we are waiting for all the
+ * request to finish from previous batch and then start
+ * the new batch. Can't wait now. Mark that full batch time
+ * needs to be allocated when this queue is scheduled again.
+ */
+ asq->current_batch_time_left =
+ ad->batch_expire[ad->batch_data_dir];
+ ad->changed_batch = 0;
+ goto out;
+ }
+
+ if (ad->new_batch) {
+ /*
+ * We should come here only when new_batch has been set
+ * but no read request has been issued or if it is a forced
+ * expiry.
+ *
+ * In both the cases, new batch has not started yet so
+ * allocate full batch length for next scheduling opportunity.
+ * We don't do write batch size adjustment in hierarchical
+ * AS so that should not be an issue.
+ */
+ asq->current_batch_time_left =
+ ad->batch_expire[ad->batch_data_dir];
+ ad->new_batch = 0;
+ goto out;
+ }
+
+ /* Save how much time is left before current batch expires */
+ if (as_batch_expired(ad, asq))
+ asq->current_batch_time_left = 0;
+ else {
+ asq->current_batch_time_left = ad->current_batch_expires
+ - jiffies;
+ BUG_ON((asq->current_batch_time_left) < 0);
+ }
+
+ if (ad->io_context) {
+ put_io_context(ad->io_context);
+ ad->io_context = NULL;
+ }
+
+out:
+ 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,
+ ad->changed_batch, ad->new_batch, ad->antic_status);
+ return;
+}
+
+/*
+ * FIXME: In original AS, read batch's time account started only after when
+ * first request had completed (if last batch was a write batch). But here
+ * we might be rescheduling a read batch right away irrespective of the fact
+ * of disk cache state.
+ */
+static void as_restore_batch_context(struct as_data *ad, struct as_queue *asq)
+{
+ /* Adjust the batch expire time */
+ if (asq->current_batch_time_left)
+ ad->current_batch_expires = jiffies +
+ asq->current_batch_time_left;
+ /* restore asq batch_data_dir info */
+ ad->batch_data_dir = asq->saved_batch_data_dir;
+ 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],
+ ad->antic_status);
+}
+
+/* ioq has been set. */
+static void as_active_ioq_set(struct request_queue *q, void *sched_queue,
+ int coop)
+{
+ struct as_queue *asq = sched_queue;
+ struct as_data *ad = q->elevator->elevator_data;
+
+ as_restore_batch_context(ad, asq);
+}
+
+/*
+ * This is a notification from common layer that it wishes to expire this
+ * io queue. AS decides whether queue can be expired, if yes, it also
+ * saves the batch context.
+ */
+static int as_expire_ioq(struct request_queue *q, void *sched_queue,
+ int slice_expired, int force)
+{
+ struct as_data *ad = q->elevator->elevator_data;
+ int status = ad->antic_status;
+ struct as_queue *asq = sched_queue;
+
+ 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) {
+ as_antic_stop(ad);
+ /*
+ * antic_stop() sets antic_status to FINISHED which signifies
+ * that either we timed out or we found a close request but
+ * that's not the case here. Start from scratch.
+ */
+ ad->antic_status = ANTIC_OFF;
+ as_save_batch_context(ad, asq);
+ ad->switch_queue = 0;
+ return 1;
+ }
+
+ /*
+ * We are waiting for requests to finish from last
+ * batch. Don't expire the queue now
+ */
+ if (ad->changed_batch)
+ goto keep_queue;
+
+ /*
+ * Wait for all requests from existing batch to finish before we
+ * switch the queue. New queue might change the batch direction
+ * and this is to be consistent with AS philosophy of not dispatching
+ * new requests to underlying drive till requests from requests
+ * from previous batch are completed.
+ */
+ if (ad->nr_dispatched)
+ goto keep_queue;
+
+ /*
+ * If AS anticipation is ON, wait for it to finish.
+ */
+ BUG_ON(status == ANTIC_WAIT_REQ);
+
+ if (status == ANTIC_WAIT_NEXT)
+ goto keep_queue;
+
+ /* We are good to expire the queue. Save batch context */
+ as_save_batch_context(ad, asq);
+ ad->switch_queue = 0;
+ return 1;
+
+keep_queue:
+ /* Mark that elevator requested for queue switch whenever possible */
+ ad->switch_queue = 1;
+ return 0;
+}
+#endif

/*
* IO Context helper functions
@@ -429,6 +621,7 @@ static void as_antic_waitnext(struct as_data *ad)
mod_timer(&ad->antic_timer, timeout);

ad->antic_status = ANTIC_WAIT_NEXT;
+ as_log(ad, "antic_waitnext set");
}

/*
@@ -442,8 +635,10 @@ static void as_antic_waitreq(struct as_data *ad)
if (ad->antic_status == ANTIC_OFF) {
if (!ad->io_context || ad->ioc_finished)
as_antic_waitnext(ad);
- else
+ else {
ad->antic_status = ANTIC_WAIT_REQ;
+ as_log(ad, "antic_waitreq set");
+ }
}
}

@@ -455,6 +650,8 @@ static void as_antic_stop(struct as_data *ad)
{
int status = ad->antic_status;

+ as_log(ad, "as_antic_stop antic_status=%d", ad->antic_status);
+
if (status == ANTIC_WAIT_REQ || status == ANTIC_WAIT_NEXT) {
if (status == ANTIC_WAIT_NEXT)
del_timer(&ad->antic_timer);
@@ -474,6 +671,7 @@ static void as_antic_timeout(unsigned long data)
unsigned long flags;

spin_lock_irqsave(q->queue_lock, flags);
+ as_log(ad, "as_antic_timeout");
if (ad->antic_status == ANTIC_WAIT_REQ
|| ad->antic_status == ANTIC_WAIT_NEXT) {
struct as_io_context *aic;
@@ -652,6 +850,21 @@ static int as_can_break_anticipation(struct as_data *ad, struct request *rq)
struct io_context *ioc;
struct as_io_context *aic;

+#ifdef CONFIG_IOSCHED_AS_HIER
+ /*
+ * If the active asq and rq's asq are not same, then one can not
+ * break the anticipation. This primarily becomes useful when a
+ * request is added to a queue which is not being served currently.
+ */
+ if (rq) {
+ struct as_queue *asq = elv_get_sched_queue(ad->q, rq);
+ struct as_queue *curr_asq =
+ elv_active_sched_queue(ad->q->elevator);
+
+ if (asq != curr_asq)
+ return 0;
+ }
+#endif
ioc = ad->io_context;
BUG_ON(!ioc);
spin_lock(&ioc->lock);
@@ -810,16 +1023,21 @@ static void as_update_rq(struct as_data *ad, struct request *rq)
/*
* Gathers timings and resizes the write batch automatically
*/
-static void update_write_batch(struct as_data *ad)
+static void update_write_batch(struct as_data *ad, struct request *rq)
{
unsigned long batch = ad->batch_expire[BLK_RW_ASYNC];
long write_time;
- struct as_queue *asq = elv_get_sched_queue(ad->q, NULL);
+ struct as_queue *asq = elv_get_sched_queue(ad->q, rq);

write_time = (jiffies - ad->current_batch_expires) + batch;
if (write_time < 0)
write_time = 0;

+ 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)
asq->write_batch_count /= 2;
@@ -834,6 +1052,8 @@ static void update_write_batch(struct as_data *ad)

if (asq->write_batch_count < 1)
asq->write_batch_count = 1;
+
+ as_log_asq(ad, asq, "upd write count=%d", asq->write_batch_count);
}

/*
@@ -843,6 +1063,7 @@ static void update_write_batch(struct as_data *ad)
static void as_completed_request(struct request_queue *q, struct request *rq)
{
struct as_data *ad = q->elevator->elevator_data;
+ struct as_queue *asq = elv_get_sched_queue(q, rq);

WARN_ON(!list_empty(&rq->queuelist));

@@ -851,7 +1072,24 @@ static void as_completed_request(struct request_queue *q, struct request *rq)
goto out;
}

+ 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,
+ ad->batch_data_dir ? 'R' : 'W');
+
if (ad->changed_batch && ad->nr_dispatched == 1) {
+ /*
+ * If this was write batch finishing, adjust the write batch
+ * length.
+ *
+ * Note, write batch length is being calculated upon completion
+ * of last write request finished and not completion of first
+ * read request finished in the next batch.
+ */
+ if (ad->batch_data_dir == BLK_RW_SYNC)
+ update_write_batch(ad, rq);
+
ad->current_batch_expires = jiffies +
ad->batch_expire[ad->batch_data_dir];
kblockd_schedule_work(q, &ad->antic_work);
@@ -869,7 +1107,6 @@ static void as_completed_request(struct request_queue *q, struct request *rq)
* and writeback caches
*/
if (ad->new_batch && ad->batch_data_dir == rq_is_sync(rq)) {
- update_write_batch(ad);
ad->current_batch_expires = jiffies +
ad->batch_expire[BLK_RW_SYNC];
ad->new_batch = 0;
@@ -888,6 +1125,13 @@ static void as_completed_request(struct request_queue *q, struct request *rq)
}

as_put_io_context(rq);
+
+ /*
+ * If elevator requested a queue switch, kick the queue in the
+ * hope that this is right time for switch.
+ */
+ if (ad->switch_queue)
+ kblockd_schedule_work(q, &ad->antic_work);
out:
RQ_SET_STATE(rq, AS_RQ_POSTSCHED);
}
@@ -908,6 +1152,9 @@ static void as_remove_queued_request(struct request_queue *q,

WARN_ON(RQ_STATE(rq) != AS_RQ_QUEUED);

+ BUG_ON(asq->nr_queued[data_dir] <= 0);
+ asq->nr_queued[data_dir]--;
+
ioc = RQ_IOC(rq);
if (ioc && ioc->aic) {
BUG_ON(!atomic_read(&ioc->aic->nr_queued));
@@ -1019,6 +1266,8 @@ 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_asq(ad, asq, "dispatch req dir=%c nr_dispatched = %d",
+ data_dir ? 'R' : 'W', ad->nr_dispatched);
}

/*
@@ -1066,6 +1315,7 @@ static int as_dispatch_request(struct request_queue *q, int force)
}
asq->last_check_fifo[BLK_RW_ASYNC] = jiffies;

+ as_log_asq(ad, asq, "forced dispatch");
return dispatched;
}

@@ -1078,8 +1328,14 @@ static int as_dispatch_request(struct request_queue *q, int force)
if (!(reads || writes)
|| ad->antic_status == ANTIC_WAIT_REQ
|| ad->antic_status == ANTIC_WAIT_NEXT
- || ad->changed_batch)
+ || ad->changed_batch) {
+ 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,
+ ad->switch_queue, ad->new_batch);
return 0;
+ }

if (!(reads && writes && as_batch_expired(ad, asq))) {
/*
@@ -1092,6 +1348,7 @@ static int as_dispatch_request(struct request_queue *q, int force)
goto fifo_expired;

if (as_can_anticipate(ad, rq)) {
+ as_log_asq(ad, asq, "can_anticipate = 1");
as_antic_waitreq(ad);
return 0;
}
@@ -1111,6 +1368,8 @@ static int as_dispatch_request(struct request_queue *q, int force)
* data direction (read / write)
*/

+ as_log_asq(ad, asq, "select a fresh batch and request");
+
if (reads) {
BUG_ON(RB_EMPTY_ROOT(&asq->sort_list[BLK_RW_SYNC]));

@@ -1125,6 +1384,7 @@ static int as_dispatch_request(struct request_queue *q, int force)
ad->changed_batch = 1;
}
ad->batch_data_dir = BLK_RW_SYNC;
+ as_log_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;
@@ -1149,6 +1409,7 @@ dispatch_writes:
ad->new_batch = 0;
}
ad->batch_data_dir = BLK_RW_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);
@@ -1184,6 +1445,9 @@ fifo_expired:
ad->changed_batch = 0;
}

+ if (ad->switch_queue)
+ return 0;
+
/*
* rq is the selected appropriate request.
*/
@@ -1207,6 +1471,11 @@ 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_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]);
+
if (RQ_IOC(rq)) {
as_update_iohist(ad, RQ_IOC(rq)->aic, rq);
atomic_inc(&RQ_IOC(rq)->aic->nr_queued);
@@ -1358,6 +1627,7 @@ 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;
}
@@ -1408,6 +1678,7 @@ static void *as_init_queue(struct request_queue *q, struct elevator_queue *eq)
ad->batch_expire[BLK_RW_ASYNC] = default_write_batch_expire;

ad->current_batch_expires = jiffies + ad->batch_expire[BLK_RW_SYNC];
+ ad->switch_queue = 0;

return ad;
}
@@ -1493,6 +1764,11 @@ static struct elv_fs_entry as_attrs[] = {
AS_ATTR(antic_expire),
AS_ATTR(read_batch_expire),
AS_ATTR(write_batch_expire),
+#ifdef CONFIG_IOSCHED_AS_HIER
+ ELV_ATTR(fairness),
+ ELV_ATTR(slice_sync),
+ ELV_ATTR(group_idle),
+#endif
__ATTR_NULL
};

@@ -1514,8 +1790,14 @@ static struct elevator_type iosched_as = {
.trim = as_trim,
.elevator_alloc_sched_queue_fn = as_alloc_as_queue,
.elevator_free_sched_queue_fn = as_free_as_queue,
+#ifdef CONFIG_IOSCHED_AS_HIER
+ .elevator_expire_ioq_fn = as_expire_ioq,
+ .elevator_active_ioq_set_fn = as_active_ioq_set,
},
-
+ .elevator_features = ELV_IOSCHED_NEED_FQ | ELV_IOSCHED_SINGLE_IOQ,
+#else
+ },
+#endif
.elevator_attrs = as_attrs,
.elevator_name = "anticipatory",
.elevator_owner = THIS_MODULE,
diff --git a/block/elevator-fq.c b/block/elevator-fq.c
index a8865e1..0849bb1 100644
--- a/block/elevator-fq.c
+++ b/block/elevator-fq.c
@@ -2692,6 +2692,7 @@ static void __elv_set_active_ioq(struct elv_fq_data *efqd, struct io_queue *ioq,
elv_clear_ioq_must_dispatch(ioq);
elv_clear_iog_wait_busy_done(iog);
elv_mark_ioq_slice_new(ioq);
+ elv_clear_ioq_must_expire(ioq);

del_timer(&efqd->idle_slice_timer);
}
@@ -2793,6 +2794,49 @@ static void elv_del_ioq_busy(struct elevator_queue *e, struct io_queue *ioq,
}

/*
+ * Call iosched to let that elevator wants to expire the queue. This gives
+ * iosched like AS to say no (if it is in the middle of batch changeover or
+ * it is anticipating). it also allows iosched to do some house keeping
+ *
+ * force--> it is force dispatch and iosched must clean up its state. This
+ * is useful when elevator wants to drain iosched and wants to
+ * expire currnent active queue.
+ *
+ * slice_expired--> if 1, ioq slice expired hence elevator fair queuing logic
+ * wants to switch the queue. iosched should allow that until
+ * and unless necessary. Currently AS can deny the switch if
+ * in the middle of batch switch.
+ *
+ * if 0, time slice is still remaining. It is up to the iosched
+ * whether it wants to wait on this queue or just want to
+ * expire it and move on to next queue.
+ *
+ */
+static int elv_iosched_expire_ioq(struct request_queue *q, int slice_expired,
+ int force)
+{
+ struct elevator_queue *e = q->elevator;
+ struct io_queue *ioq = elv_active_ioq(q->elevator);
+ int ret = 1;
+
+ if (e->ops->elevator_expire_ioq_fn) {
+ ret = e->ops->elevator_expire_ioq_fn(q, ioq->sched_queue,
+ slice_expired, force);
+ /*
+ * AS denied expiration of queue right now. Mark that elevator
+ * layer has requested ioscheduler (as) to expire this queue.
+ * Now as will try to expire this queue as soon as it can.
+ * Now don't try to dispatch from this queue even if we get
+ * a new request and if time slice is left. Do expire it once.
+ */
+ if (!ret)
+ elv_mark_ioq_must_expire(ioq);
+ }
+
+ return ret;
+}
+
+/*
* Do the accounting. Determine how much service (in terms of time slices)
* current queue used and adjust the start, finish time of queue and vtime
* of the tree accordingly.
@@ -2831,6 +2875,7 @@ void __elv_ioq_slice_expired(struct request_queue *q, struct io_queue *ioq)
elv_clear_iog_wait_request(iog);
elv_clear_iog_wait_busy(iog);
elv_clear_iog_wait_busy_done(iog);
+ elv_clear_ioq_must_expire(ioq);

slice_used = jiffies - ioq->slice_start;
if (!slice_used) {
@@ -2964,16 +3009,18 @@ static int elv_should_preempt(struct request_queue *q, struct io_queue *new_ioq,
static void elv_preempt_queue(struct request_queue *q, struct io_queue *ioq)
{
elv_log_ioq(&q->elevator->efqd, ioq, "preempt");
- elv_ioq_slice_expired(q);
+ if (elv_iosched_expire_ioq(q, 0, 1)) {
+ elv_ioq_slice_expired(q);

- /*
- * Put the new queue at the front of the of the current list,
- * so we know that it will be selected next.
- */
+ /*
+ * Put the new queue at the front of the of the current list,
+ * so we know that it will be selected next.
+ */

- elv_activate_ioq(ioq, 1);
- ioq->slice_end = 0;
- elv_mark_ioq_slice_new(ioq);
+ elv_activate_ioq(ioq, 1);
+ ioq->slice_end = 0;
+ elv_mark_ioq_slice_new(ioq);
+ }
}

void elv_ioq_request_add(struct request_queue *q, struct request *rq)
@@ -3177,6 +3224,8 @@ void *elv_fq_select_ioq(struct request_queue *q, int force)
struct elv_fq_data *efqd = &q->elevator->efqd;
struct io_queue *new_ioq = NULL, *ioq = elv_active_ioq(q->elevator);
struct io_group *iog;
+ struct elevator_type *e = q->elevator->elevator_type;
+ int slice_expired = 1;

if (!elv_nr_busy_ioq(q->elevator))
return NULL;
@@ -3197,6 +3246,10 @@ void *elv_fq_select_ioq(struct request_queue *q, int force)
goto expire;
}

+ /* This queue has been marked for expiry. Try to expire it */
+ if (elv_ioq_must_expire(ioq))
+ goto expire;
+
/*
* If there is only root group present, don't expire the queue for
* single queue ioschedulers (noop, deadline, AS). It is unnecessary
@@ -3289,8 +3342,10 @@ void *elv_fq_select_ioq(struct request_queue *q, int force)
goto keep_queue;
}

+ slice_expired = 0;
expire:
- if (efqd->fairness && !force && ioq && ioq->dispatched) {
+ if (efqd->fairness && !force && ioq && ioq->dispatched
+ && strcmp(e->elevator_name, "anticipatory")) {
/*
* If there are request dispatched from this queue, don't
* dispatch requests from new queue till all the requests from
@@ -3301,6 +3356,11 @@ expire:
*
* Set ioq = NULL so that no more requests are dispatched from
* this queue.
+ *
+ * Note: Anticipatory already has the behavior where queue
+ * switch is not allowed until requests from previous queue
+ * have finished. Hence we don't have to get into this loop
+ * in case of AS.
*/
elv_log_ioq(efqd, ioq, "select: wait for requests to finish"
" disp=%lu", ioq->dispatched);
@@ -3308,7 +3368,14 @@ expire:
goto keep_queue;
}

- elv_ioq_slice_expired(q);
+ if (elv_iosched_expire_ioq(q, slice_expired, force))
+ elv_ioq_slice_expired(q);
+ else
+ /*
+ * Not making ioq = NULL, as AS can deny queue expiration and
+ * continue to dispatch from same queue
+ */
+ goto keep_queue;
new_queue:
ioq = elv_set_active_ioq(q, new_ioq);
keep_queue:
@@ -3408,7 +3475,8 @@ void elv_ioq_completed_request(struct request_queue *q, struct request *rq)
}

if (elv_ioq_class_idle(ioq)) {
- elv_ioq_slice_expired(q);
+ if (elv_iosched_expire_ioq(q, 1, 0))
+ elv_ioq_slice_expired(q);
goto done;
}

@@ -3456,7 +3524,8 @@ void elv_ioq_completed_request(struct request_queue *q, struct request *rq)
goto done;

/* Expire the queue */
- elv_ioq_slice_expired(q);
+ if (elv_iosched_expire_ioq(q, 1, 0))
+ elv_ioq_slice_expired(q);
} else if (!ioq->nr_queued && !elv_close_cooperator(q, ioq)
&& sync && !rq_noidle(rq))
elv_ioq_arm_slice_timer(q);
diff --git a/block/elevator-fq.h b/block/elevator-fq.h
index 56aa082..9715fc5 100644
--- a/block/elevator-fq.h
+++ b/block/elevator-fq.h
@@ -370,6 +370,8 @@ enum elv_queue_state_flags {
ELV_QUEUE_FLAG_wait_request, /* waiting for a request */
ELV_QUEUE_FLAG_must_dispatch, /* must be allowed a dispatch */
ELV_QUEUE_FLAG_slice_new, /* no requests dispatched in slice */
+ ELV_QUEUE_FLAG_must_expire, /* Expire this queue even if it has
+ * request and time slice left */
};

#define ELV_IO_QUEUE_FLAG_FNS(name) \
@@ -392,6 +394,7 @@ ELV_IO_QUEUE_FLAG_FNS(wait_request)
ELV_IO_QUEUE_FLAG_FNS(must_dispatch)
ELV_IO_QUEUE_FLAG_FNS(idle_window)
ELV_IO_QUEUE_FLAG_FNS(slice_new)
+ELV_IO_QUEUE_FLAG_FNS(must_expire)

#ifdef CONFIG_GROUP_IOSCHED

diff --git a/include/linux/elevator.h b/include/linux/elevator.h
index 2777cc1..d944c24 100644
--- a/include/linux/elevator.h
+++ b/include/linux/elevator.h
@@ -42,6 +42,7 @@ typedef int (elevator_should_preempt_fn) (struct request_queue*, void*,
struct request*);
typedef struct io_queue* (elevator_close_cooperator_fn) (struct request_queue*,
void*);
+typedef int (elevator_expire_ioq_fn) (struct request_queue*, void *, int, int);
#endif

struct elevator_ops
@@ -80,6 +81,7 @@ struct elevator_ops
elevator_arm_slice_timer_fn *elevator_arm_slice_timer_fn;
elevator_should_preempt_fn *elevator_should_preempt_fn;
elevator_close_cooperator_fn *elevator_close_cooperator_fn;
+ elevator_expire_ioq_fn *elevator_expire_ioq_fn;
#endif
};

--
1.6.0.6


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