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authorBart Van Assche <bvanassche@acm.org>2021-06-17 17:44:56 -0700
committerJens Axboe <axboe@kernel.dk>2021-06-21 15:03:41 -0600
commitfb926032b3209300f9dc454a36b8299582ae545c (patch)
tree411a2d4709a8caa68aa74b4c7bcd354065bc0b64
parent08a9ad8bf607388d768a341957d53eae64250c2d (diff)
block/mq-deadline: Prioritize high-priority requests
While one or more requests with a certain I/O priority are pending, do not dispatch lower priority requests. Dispatch lower priority requests anyway after the "aging" time has expired. This patch has been tested as follows: modprobe scsi_debug ndelay=1000000 max_queue=16 && sd='' && while [ -z "$sd" ]; do sd=/dev/$(basename /sys/bus/pseudo/drivers/scsi_debug/adapter*/host*/target*/*/block/*) done && echo $((100*1000)) > /sys/block/$sd/queue/iosched/aging_expire && cd /sys/fs/cgroup/blkio/ && echo $$ >cgroup.procs && echo restrict-to-be >blkio.prio.class && mkdir -p hipri && cd hipri && echo none-to-rt >blkio.prio.class && { max-iops -a1 -d32 -j1 -e mq-deadline $sd >& ~/low-pri.txt & } && echo $$ >cgroup.procs && max-iops -a1 -d32 -j1 -e mq-deadline $sd >& ~/hi-pri.txt Result: * 11000 IOPS for the high-priority job * 40 IOPS for the low-priority job If the aging expiry time is changed from 100s into 0, the IOPS results change into 6712 and 6796 IOPS. The max-iops script is a script that runs fio with the following arguments: --bs=4K --gtod_reduce=1 --ioengine=libaio --ioscheduler=${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} Reviewed-by: Damien Le Moal <damien.lemoal@wdc.com> Cc: Hannes Reinecke <hare@suse.de> Cc: Christoph Hellwig <hch@lst.de> Cc: Ming Lei <ming.lei@redhat.com> Cc: Johannes Thumshirn <johannes.thumshirn@wdc.com> Cc: Himanshu Madhani <himanshu.madhani@oracle.com> Signed-off-by: Bart Van Assche <bvanassche@acm.org> Link: https://lore.kernel.org/r/20210618004456.7280-17-bvanassche@acm.org Signed-off-by: Jens Axboe <axboe@kernel.dk>
-rw-r--r--block/mq-deadline-main.c42
1 files changed, 37 insertions, 5 deletions
diff --git a/block/mq-deadline-main.c b/block/mq-deadline-main.c
index 58a401ea8f56..4815e536091f 100644
--- a/block/mq-deadline-main.c
+++ b/block/mq-deadline-main.c
@@ -32,6 +32,11 @@
*/
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 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. */
@@ -94,6 +99,7 @@ struct deadline_data {
int writes_starved;
int front_merges;
u32 async_depth;
+ int aging_expire;
spinlock_t lock;
spinlock_t zone_lock;
@@ -361,10 +367,11 @@ deadline_next_request(struct deadline_data *dd, struct dd_per_prio *per_prio,
/*
* 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,
+ u64 latest_start_ns)
{
struct request *rq, *next_rq;
enum dd_data_dir data_dir;
@@ -377,6 +384,8 @@ 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 (rq->start_time_ns > latest_start_ns)
+ return NULL;
list_del_init(&rq->queuelist);
goto done;
}
@@ -454,6 +463,8 @@ dispatch_find_request:
dd->batching = 0;
dispatch_request:
+ if (rq->start_time_ns > latest_start_ns)
+ return NULL;
/*
* rq is the selected appropriate request.
*/
@@ -484,15 +495,32 @@ done:
static struct request *dd_dispatch_request(struct blk_mq_hw_ctx *hctx)
{
struct deadline_data *dd = hctx->queue->elevator->elevator_data;
- struct request *rq;
+ const u64 now_ns = ktime_get_ns();
+ struct request *rq = NULL;
enum dd_prio prio;
spin_lock(&dd->lock);
- for (prio = 0; prio <= DD_PRIO_MAX; prio++) {
- rq = __dd_dispatch_request(dd, &dd->per_prio[prio]);
+ /*
+ * Start with dispatching requests whose deadline expired more than
+ * aging_expire jiffies ago.
+ */
+ for (prio = DD_BE_PRIO; prio <= DD_PRIO_MAX; prio++) {
+ rq = __dd_dispatch_request(dd, &dd->per_prio[prio], now_ns -
+ jiffies_to_nsecs(dd->aging_expire));
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], now_ns);
+ if (rq || dd_queued(dd, prio))
break;
}
+
+unlock:
spin_unlock(&dd->lock);
return rq;
@@ -603,6 +631,7 @@ 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->aging_expire = aging_expire;
spin_lock_init(&dd->lock);
spin_lock_init(&dd->zone_lock);
@@ -835,6 +864,7 @@ 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_aging_expire_show, dd->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);
@@ -864,6 +894,7 @@ 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_aging_expire_store, &dd->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);
@@ -882,6 +913,7 @@ static struct elv_fs_entry deadline_attrs[] = {
DD_ATTR(front_merges),
DD_ATTR(async_depth),
DD_ATTR(fifo_batch),
+ DD_ATTR(aging_expire),
__ATTR_NULL
};