[PATCH 2/4] block: Implement a blk_yield function to voluntarily give up the I/O scheduler.
From: Jeff Moyer
Date: Wed Apr 14 2010 - 17:17:18 EST
This patch implements a blk_yield to allow a process to voluntarily
give up its I/O scheduler time slice. This is desirable for those processes
which know that they will be blocked on I/O from another process, such as
the file system journal thread. Following patches will put calls to blk_yield
into jbd and jbd2.
Signed-off-by: Jeff Moyer <jmoyer@xxxxxxxxxx>
---
block/blk-core.c | 6 ++++
block/cfq-iosched.c | 70 ++++++++++++++++++++++++++++++++++++++++++++++
block/elevator.c | 8 +++++
include/linux/blkdev.h | 1 +
include/linux/elevator.h | 3 ++
5 files changed, 88 insertions(+), 0 deletions(-)
diff --git a/block/blk-core.c b/block/blk-core.c
index 9fe174d..3e4e98c 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -323,6 +323,12 @@ void blk_unplug(struct request_queue *q)
}
EXPORT_SYMBOL(blk_unplug);
+void blk_yield(struct request_queue *q)
+{
+ elv_yield(q);
+}
+EXPORT_SYMBOL(blk_yield);
+
/**
* blk_start_queue - restart a previously stopped queue
* @q: The &struct request_queue in question
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index ef59ab3..8a300ab 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -292,6 +292,7 @@ struct cfq_data {
};
static struct cfq_group *cfq_get_next_cfqg(struct cfq_data *cfqd);
+static void cfq_yield_cfqq(struct cfq_data *cfqd, struct cfq_queue *cfqq);
static struct cfq_rb_root *service_tree_for(struct cfq_group *cfqg,
enum wl_prio_t prio,
@@ -320,6 +321,7 @@ enum cfqq_state_flags {
CFQ_CFQQ_FLAG_split_coop, /* shared cfqq will be splitted */
CFQ_CFQQ_FLAG_deep, /* sync cfqq experienced large depth */
CFQ_CFQQ_FLAG_wait_busy, /* Waiting for next request */
+ CFQ_CFQQ_FLAG_yield, /* Allow another cfqq to run */
};
#define CFQ_CFQQ_FNS(name) \
@@ -349,6 +351,7 @@ CFQ_CFQQ_FNS(coop);
CFQ_CFQQ_FNS(split_coop);
CFQ_CFQQ_FNS(deep);
CFQ_CFQQ_FNS(wait_busy);
+CFQ_CFQQ_FNS(yield);
#undef CFQ_CFQQ_FNS
#ifdef CONFIG_DEBUG_CFQ_IOSCHED
@@ -1566,6 +1569,7 @@ __cfq_slice_expired(struct cfq_data *cfqd, struct cfq_queue *cfqq,
cfq_clear_cfqq_wait_request(cfqq);
cfq_clear_cfqq_wait_busy(cfqq);
+ cfq_clear_cfqq_yield(cfqq);
/*
* If this cfqq is shared between multiple processes, check to
@@ -1887,6 +1891,9 @@ static void cfq_dispatch_insert(struct request_queue *q, struct request *rq)
cfqd->rq_in_flight[cfq_cfqq_sync(cfqq)]++;
cfqq->nr_sectors += blk_rq_sectors(rq);
+
+ if (cfq_cfqq_yield(cfqq) && RB_EMPTY_ROOT(&cfqq->sort_list))
+ cfq_yield_cfqq(cfqd, cfqq);
}
/*
@@ -2191,6 +2198,68 @@ keep_queue:
return cfqq;
}
+static void cfq_yield_cfqq(struct cfq_data *cfqd, struct cfq_queue *cfqq)
+{
+ __cfq_slice_expired(cfqd, cfqq, 1);
+ __blk_run_queue(cfqd->queue);
+}
+
+static void cfq_yield(struct request_queue *q)
+{
+ struct cfq_data *cfqd = q->elevator->elevator_data;
+ struct cfq_io_context *cic;
+ struct cfq_queue *cfqq;
+
+ cic = cfq_cic_lookup(cfqd, current->io_context);
+ if (!cic)
+ return;
+
+ spin_lock_irq(q->queue_lock);
+
+ /*
+ * This is primarily called to ensure that the long synchronous
+ * time slice does not prevent other I/O happenning (like journal
+ * commits) while we idle waiting for it. Thus, check to see if the
+ * current cfqq is the sync cfqq for this process.
+ */
+ cfqq = cic_to_cfqq(cic, 1);
+ if (!cfqq)
+ goto out_unlock;
+
+ if (cfqd->active_queue != cfqq)
+ goto out_unlock;
+
+ /*
+ * If we are currently servicing the SYNC_NOIDLE_WORKLOAD, and we
+ * are idling on the last queue in that workload, *and* the average
+ * think time is larger thank the remaining slice time, go ahead
+ * and yield the queue. Otherwise, don't yield so that fsync-heavy
+ * workloads don't starve out the sync-noidle workload.
+ */
+ if (cfqd->serving_type == SYNC_NOIDLE_WORKLOAD &&
+ (!sample_valid(cfqq->service_tree->ttime_samples) ||
+ cfqq->slice_end - jiffies > cfqq->service_tree->ttime_mean))
+ goto out_unlock;
+
+
+ cfq_log_cfqq(cfqd, cfqq, "yielding queue");
+
+ /*
+ * If there are other requests pending, just mark the queue as
+ * yielding and give up our slice after the last request is
+ * dispatched.
+ */
+ if (!RB_EMPTY_ROOT(&cfqq->sort_list)) {
+ cfq_mark_cfqq_yield(cfqq);
+ goto out_unlock;
+ }
+
+ cfq_yield_cfqq(cfqd, cfqq);
+
+out_unlock:
+ spin_unlock_irq(q->queue_lock);
+}
+
static int __cfq_forced_dispatch_cfqq(struct cfq_queue *cfqq)
{
int dispatched = 0;
@@ -3911,6 +3980,7 @@ static struct elevator_type iosched_cfq = {
.elevator_deactivate_req_fn = cfq_deactivate_request,
.elevator_queue_empty_fn = cfq_queue_empty,
.elevator_completed_req_fn = cfq_completed_request,
+ .elevator_yield_fn = cfq_yield,
.elevator_former_req_fn = elv_rb_former_request,
.elevator_latter_req_fn = elv_rb_latter_request,
.elevator_set_req_fn = cfq_set_request,
diff --git a/block/elevator.c b/block/elevator.c
index 76e3702..6b16421 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -855,6 +855,14 @@ void elv_completed_request(struct request_queue *q, struct request *rq)
}
}
+void elv_yield(struct request_queue *q)
+{
+ struct elevator_queue *e = q->elevator;
+
+ if (e && e->ops->elevator_yield_fn)
+ e->ops->elevator_yield_fn(q);
+}
+
#define to_elv(atr) container_of((atr), struct elv_fs_entry, attr)
static ssize_t
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 6690e8b..0e749e2 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -833,6 +833,7 @@ extern int blk_execute_rq(struct request_queue *, struct gendisk *,
extern void blk_execute_rq_nowait(struct request_queue *, struct gendisk *,
struct request *, int, rq_end_io_fn *);
extern void blk_unplug(struct request_queue *q);
+extern void blk_yield(struct request_queue *q);
static inline struct request_queue *bdev_get_queue(struct block_device *bdev)
{
diff --git a/include/linux/elevator.h b/include/linux/elevator.h
index 1cb3372..9b4e2e9 100644
--- a/include/linux/elevator.h
+++ b/include/linux/elevator.h
@@ -20,6 +20,7 @@ typedef void (elevator_add_req_fn) (struct request_queue *, struct request *);
typedef int (elevator_queue_empty_fn) (struct request_queue *);
typedef struct request *(elevator_request_list_fn) (struct request_queue *, struct request *);
typedef void (elevator_completed_req_fn) (struct request_queue *, struct request *);
+typedef void (elevator_yield_fn) (struct request_queue *);
typedef int (elevator_may_queue_fn) (struct request_queue *, int);
typedef int (elevator_set_req_fn) (struct request_queue *, struct request *, gfp_t);
@@ -44,6 +45,7 @@ struct elevator_ops
elevator_queue_empty_fn *elevator_queue_empty_fn;
elevator_completed_req_fn *elevator_completed_req_fn;
+ elevator_yield_fn *elevator_yield_fn;
elevator_request_list_fn *elevator_former_req_fn;
elevator_request_list_fn *elevator_latter_req_fn;
@@ -105,6 +107,7 @@ extern void elv_merge_requests(struct request_queue *, struct request *,
extern void elv_merged_request(struct request_queue *, struct request *, int);
extern void elv_requeue_request(struct request_queue *, struct request *);
extern int elv_queue_empty(struct request_queue *);
+extern void elv_yield(struct request_queue *);
extern struct request *elv_former_request(struct request_queue *, struct request *);
extern struct request *elv_latter_request(struct request_queue *, struct request *);
extern int elv_register_queue(struct request_queue *q);
--
1.6.2.5
--
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