In addition to reverting commit 7b05bf771084 ("Revert "block/mq-deadline:
Prioritize high-priority requests""), this patch uses 'jiffies' instead
of ktime_get() in the code for aging lower priority requests.
This patch has been tested as follows:
Measured QD=1/jobs=1 IOPS for nullb with the mq-deadline scheduler.
Result without and with this patch: 555 K IOPS.
Measured QD=1/jobs=8 IOPS for nullb with the mq-deadline scheduler.
Result without and with this patch: about 380 K IOPS.
Ran the following script:
set -e
scriptdir=$(dirname "$0")
if [ -e /sys/module/scsi_debug ]; then modprobe -r scsi_debug; fi
modprobe scsi_debug ndelay=1000000 max_queue=16
sd=''
while [ -z "$sd" ]; do
sd=$(basename /sys/bus/pseudo/drivers/scsi_debug/adapter*/host*/target*/*/block/*)
done
echo $((100*1000)) > "/sys/block/$sd/queue/iosched/prio_aging_expire"
if [ -e /sys/fs/cgroup/io.prio.class ]; then
cd /sys/fs/cgroup
echo restrict-to-be >io.prio.class
echo +io > cgroup.subtree_control
else
cd /sys/fs/cgroup/blkio/
echo restrict-to-be >blkio.prio.class
fi
echo $$ >cgroup.procs
mkdir -p hipri
cd hipri
if [ -e io.prio.class ]; then
echo none-to-rt >io.prio.class
else
echo none-to-rt >blkio.prio.class
fi
{ "${scriptdir}/max-iops" -a1 -d32 -j1 -e mq-deadline "/dev/$sd" >& ~/low-pri.txt & }
echo $$ >cgroup.procs
"${scriptdir}/max-iops" -a1 -d32 -j1 -e mq-deadline "/dev/$sd" >& ~/hi-pri.txt
Result:
* 11000 IOPS for the high-priority job
* 40 IOPS for the low-priority job
If the prio aging expiry time is changed from 100s into 0, the IOPS results
change into 6712 and 6796 IOPS.
The max-iops script is a script that runs fio with the following arguments:
--bs=4K --gtod_reduce=1 --ioengine=libaio --ioscheduler=${arg_e} --runtime=60
--norandommap --rw=read --thread --buffered=0 --numjobs=${arg_j}
--iodepth=${arg_d} --iodepth_batch_submit=${arg_a}
--iodepth_batch_complete=$((arg_d / 2)) --name=${positional_argument_1}
--filename=${positional_argument_1}
Cc: Damien Le Moal <damien.lemoal@xxxxxxx>
Cc: Niklas Cassel <Niklas.Cassel@xxxxxxx>
Cc: Hannes Reinecke <hare@xxxxxxx>
Signed-off-by: Bart Van Assche <bvanassche@xxxxxxx>
---
block/mq-deadline.c | 77 ++++++++++++++++++++++++++++++++++++++++++---
1 file changed, 73 insertions(+), 4 deletions(-)
diff --git a/block/mq-deadline.c b/block/mq-deadline.c
index b262f40f32c0..bb723478baf1 100644
--- a/block/mq-deadline.c
+++ b/block/mq-deadline.c
@@ -31,6 +31,11 @@
*/
static const int read_expire = HZ / 2; /* max time before a read is submitted. */
static const int write_expire = 5 * HZ; /* ditto for writes, these limits are SOFT! */
+/*
+ * Time after which to dispatch lower priority requests even if higher
+ * priority requests are pending.
+ */
+static const int prio_aging_expire = 10 * HZ;
static const int writes_starved = 2; /* max times reads can starve a write */
static const int fifo_batch = 16; /* # of sequential requests treated as one
by the above parameters. For throughput. */
@@ -96,6 +101,7 @@ struct deadline_data {
int writes_starved;
int front_merges;
u32 async_depth;
+ int prio_aging_expire;
spinlock_t lock;
spinlock_t zone_lock;
@@ -338,12 +344,27 @@ deadline_next_request(struct deadline_data *dd, struct dd_per_prio *per_prio,
return rq;
}
+/*
+ * Returns true if and only if @rq started after @latest_start where
+ * @latest_start is in jiffies.
+ */
+static bool started_after(struct deadline_data *dd, struct request *rq,
+ unsigned long latest_start)
+{
+ unsigned long start_time = (unsigned long)rq->fifo_time;
+
+ start_time -= dd->fifo_expire[rq_data_dir(rq)];
+
+ return time_after(start_time, latest_start);
+}
+
/*
* deadline_dispatch_requests selects the best request according to
- * read/write expire, fifo_batch, etc
+ * read/write expire, fifo_batch, etc and with a start time <= @latest.
*/
static struct request *__dd_dispatch_request(struct deadline_data *dd,
- struct dd_per_prio *per_prio)
+ struct dd_per_prio *per_prio,
+ unsigned long latest_start)
{
struct request *rq, *next_rq;
enum dd_data_dir data_dir;
@@ -355,6 +376,8 @@ static struct request *__dd_dispatch_request(struct deadline_data *dd,
if (!list_empty(&per_prio->dispatch)) {
rq = list_first_entry(&per_prio->dispatch, struct request,
queuelist);
+ if (started_after(dd, rq, latest_start))
+ return NULL;
list_del_init(&rq->queuelist);
goto done;
}
@@ -432,6 +455,9 @@ static struct request *__dd_dispatch_request(struct deadline_data *dd,
dd->batching = 0;
dispatch_request:
+ if (started_after(dd, rq, latest_start))
+ return NULL;
+
/*
* rq is the selected appropriate request.
*/
@@ -449,6 +475,34 @@ static struct request *__dd_dispatch_request(struct deadline_data *dd,
return rq;
}
+/*
+ * Check whether there are any requests with priority other than DD_RT_PRIO
+ * that were inserted more than prio_aging_expire jiffies ago.
+ */
+static struct request *dd_dispatch_prio_aged_requests(struct deadline_data *dd,
+ unsigned long now)
+{
+ struct request *rq;
+ enum dd_prio prio;
+ int prio_cnt;
+
+ lockdep_assert_held(&dd->lock);
+
+ prio_cnt = !!dd_queued(dd, DD_RT_PRIO) + !!dd_queued(dd, DD_BE_PRIO) +
+ !!dd_queued(dd, DD_IDLE_PRIO);
+ if (prio_cnt < 2)
+ return NULL;
+
+ for (prio = DD_BE_PRIO; prio <= DD_PRIO_MAX; prio++) {
+ rq = __dd_dispatch_request(dd, &dd->per_prio[prio],
+ now - dd->prio_aging_expire);
+ if (rq)
+ return rq;
+ }
+
+ return NULL;
+}
+
/*
* Called from blk_mq_run_hw_queue() -> __blk_mq_sched_dispatch_requests().
*
@@ -460,15 +514,26 @@ static struct request *__dd_dispatch_request(struct deadline_data *dd,
static struct request *dd_dispatch_request(struct blk_mq_hw_ctx *hctx)
{
struct deadline_data *dd = hctx->queue->elevator->elevator_data;
+ const unsigned long now = jiffies;
struct request *rq;
enum dd_prio prio;
spin_lock(&dd->lock);
+ rq = dd_dispatch_prio_aged_requests(dd, now);
+ if (rq)
+ goto unlock;
+
+ /*
+ * Next, dispatch requests in priority order. Ignore lower priority
+ * requests if any higher priority requests are pending.
+ */
for (prio = 0; prio <= DD_PRIO_MAX; prio++) {
- rq = __dd_dispatch_request(dd, &dd->per_prio[prio]);
- if (rq)
+ rq = __dd_dispatch_request(dd, &dd->per_prio[prio], now);
+ if (rq || dd_queued(dd, prio))
break;
}
+
+unlock:
spin_unlock(&dd->lock);
return rq;
@@ -573,6 +638,7 @@ static int dd_init_sched(struct request_queue *q, struct elevator_type *e)
dd->front_merges = 1;
dd->last_dir = DD_WRITE;
dd->fifo_batch = fifo_batch;
+ dd->prio_aging_expire = prio_aging_expire;
spin_lock_init(&dd->lock);
spin_lock_init(&dd->zone_lock);
@@ -796,6 +862,7 @@ static ssize_t __FUNC(struct elevator_queue *e, char *page) \
#define SHOW_JIFFIES(__FUNC, __VAR) SHOW_INT(__FUNC, jiffies_to_msecs(__VAR))
SHOW_JIFFIES(deadline_read_expire_show, dd->fifo_expire[DD_READ]);
SHOW_JIFFIES(deadline_write_expire_show, dd->fifo_expire[DD_WRITE]);
+SHOW_JIFFIES(deadline_prio_aging_expire_show, dd->prio_aging_expire);
SHOW_INT(deadline_writes_starved_show, dd->writes_starved);
SHOW_INT(deadline_front_merges_show, dd->front_merges);
SHOW_INT(deadline_async_depth_show, dd->front_merges);
@@ -825,6 +892,7 @@ static ssize_t __FUNC(struct elevator_queue *e, const char *page, size_t count)
STORE_FUNCTION(__FUNC, __PTR, MIN, MAX, msecs_to_jiffies)
STORE_JIFFIES(deadline_read_expire_store, &dd->fifo_expire[DD_READ], 0, INT_MAX);
STORE_JIFFIES(deadline_write_expire_store, &dd->fifo_expire[DD_WRITE], 0, INT_MAX);
+STORE_JIFFIES(deadline_prio_aging_expire_store, &dd->prio_aging_expire, 0, INT_MAX);
STORE_INT(deadline_writes_starved_store, &dd->writes_starved, INT_MIN, INT_MAX);
STORE_INT(deadline_front_merges_store, &dd->front_merges, 0, 1);
STORE_INT(deadline_async_depth_store, &dd->front_merges, 1, INT_MAX);
@@ -843,6 +911,7 @@ static struct elv_fs_entry deadline_attrs[] = {
DD_ATTR(front_merges),
DD_ATTR(async_depth),
DD_ATTR(fifo_batch),
+ DD_ATTR(prio_aging_expire),
__ATTR_NULL
};
