From: Bart Van Assche <bvanassche@acm.org>
Date: Mon, 27 Sep 2021 15:03:27 -0700
Subject: [PATCH] block/mq-deadline: Stop using per-CPU counters
Git-commit: bce0363ed84af8e8e27df464b2082f4b5f58b57e
Patch-mainline: v5.16-rc1
References: jsc#PED-1183
Calculating the sum over all CPUs of per-CPU counters frequently is
inefficient. Hence switch from per-CPU to individual counters. Three
counters are protected by the mq-deadline spinlock since these are
only accessed from contexts that already hold that spinlock. The fourth
counter is atomic because protecting it with the mq-deadline spinlock
would trigger lock contention.
Reviewed-by: Damien Le Moal <damien.lemoal@wdc.com>
Reviewed-by: Niklas Cassel <Niklas.Cassel@wdc.com>
Cc: Hannes Reinecke <hare@suse.de>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Link: https://lore.kernel.org/r/20210927220328.1410161-4-bvanassche@acm.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Acked-by: Hannes Reinecke <hare@suse.com>
---
block/mq-deadline.c | 124 ++++++++++++++++++++------------------------
1 file changed, 56 insertions(+), 68 deletions(-)
diff --git a/block/mq-deadline.c b/block/mq-deadline.c
index 2586b3f8c7e9..b262f40f32c0 100644
--- a/block/mq-deadline.c
+++ b/block/mq-deadline.c
@@ -51,17 +51,16 @@ enum dd_prio {
enum { DD_PRIO_COUNT = 3 };
-/* I/O statistics per I/O priority. */
+/*
+ * I/O statistics per I/O priority. It is fine if these counters overflow.
+ * What matters is that these counters are at least as wide as
+ * log2(max_outstanding_requests).
+ */
struct io_stats_per_prio {
- local_t inserted;
- local_t merged;
- local_t dispatched;
- local_t completed;
-};
-
-/* I/O statistics for all I/O priorities (enum dd_prio). */
-struct io_stats {
- struct io_stats_per_prio stats[DD_PRIO_COUNT];
+ uint32_t inserted;
+ uint32_t merged;
+ uint32_t dispatched;
+ atomic_t completed;
};
/*
@@ -74,6 +73,7 @@ struct dd_per_prio {
struct list_head fifo_list[DD_DIR_COUNT];
/* Next request in FIFO order. Read, write or both are NULL. */
struct request *next_rq[DD_DIR_COUNT];
+ struct io_stats_per_prio stats;
};
struct deadline_data {
@@ -88,8 +88,6 @@ struct deadline_data {
unsigned int batching; /* number of sequential requests made */
unsigned int starved; /* times reads have starved writes */
- struct io_stats __percpu *stats;
-
/*
* settings that change how the i/o scheduler behaves
*/
@@ -103,33 +101,6 @@ struct deadline_data {
spinlock_t zone_lock;
};
-/* Count one event of type 'event_type' and with I/O priority 'prio' */
-#define dd_count(dd, event_type, prio) do { \
- struct io_stats *io_stats = get_cpu_ptr((dd)->stats); \
- \
- BUILD_BUG_ON(!__same_type((dd), struct deadline_data *)); \
- BUILD_BUG_ON(!__same_type((prio), enum dd_prio)); \
- local_inc(&io_stats->stats[(prio)].event_type); \
- put_cpu_ptr(io_stats); \
-} while (0)
-
-/*
- * Returns the total number of dd_count(dd, event_type, prio) calls across all
- * CPUs. No locking or barriers since it is fine if the returned sum is slightly
- * outdated.
- */
-#define dd_sum(dd, event_type, prio) ({ \
- unsigned int cpu; \
- u32 sum = 0; \
- \
- BUILD_BUG_ON(!__same_type((dd), struct deadline_data *)); \
- BUILD_BUG_ON(!__same_type((prio), enum dd_prio)); \
- for_each_present_cpu(cpu) \
- sum += local_read(&per_cpu_ptr((dd)->stats, cpu)-> \
- stats[(prio)].event_type); \
- sum; \
-})
-
/* Maps an I/O priority class to a deadline scheduler priority. */
static const enum dd_prio ioprio_class_to_prio[] = {
[IOPRIO_CLASS_NONE] = DD_BE_PRIO,
@@ -233,7 +204,9 @@ static void dd_merged_requests(struct request_queue *q, struct request *req,
const u8 ioprio_class = dd_rq_ioclass(next);
const enum dd_prio prio = ioprio_class_to_prio[ioprio_class];
- dd_count(dd, merged, prio);
+ lockdep_assert_held(&dd->lock);
+
+ dd->per_prio[prio].stats.merged++;
/*
* if next expires before rq, assign its expire time to rq
@@ -273,7 +246,11 @@ deadline_move_request(struct deadline_data *dd, struct dd_per_prio *per_prio,
/* Number of requests queued for a given priority level. */
static u32 dd_queued(struct deadline_data *dd, enum dd_prio prio)
{
- return dd_sum(dd, inserted, prio) - dd_sum(dd, completed, prio);
+ const struct io_stats_per_prio *stats = &dd->per_prio[prio].stats;
+
+ lockdep_assert_held(&dd->lock);
+
+ return stats->inserted - atomic_read(&stats->completed);
}
/*
@@ -463,7 +440,7 @@ static struct request *__dd_dispatch_request(struct deadline_data *dd,
done:
ioprio_class = dd_rq_ioclass(rq);
prio = ioprio_class_to_prio[ioprio_class];
- dd_count(dd, dispatched, prio);
+ dd->per_prio[prio].stats.dispatched++;
/*
* If the request needs its target zone locked, do it.
*/
@@ -542,19 +519,22 @@ static void dd_exit_sched(struct elevator_queue *e)
for (prio = 0; prio <= DD_PRIO_MAX; prio++) {
struct dd_per_prio *per_prio = &dd->per_prio[prio];
+ const struct io_stats_per_prio *stats = &per_prio->stats;
+ uint32_t queued;
WARN_ON_ONCE(!list_empty(&per_prio->fifo_list[DD_READ]));
WARN_ON_ONCE(!list_empty(&per_prio->fifo_list[DD_WRITE]));
- WARN_ONCE(dd_queued(dd, prio) != 0,
+
+ spin_lock(&dd->lock);
+ queued = dd_queued(dd, prio);
+ spin_unlock(&dd->lock);
+
+ WARN_ONCE(queued != 0,
"statistics for priority %d: i %u m %u d %u c %u\n",
- prio, dd_sum(dd, inserted, prio),
- dd_sum(dd, merged, prio),
- dd_sum(dd, dispatched, prio),
- dd_sum(dd, completed, prio));
+ prio, stats->inserted, stats->merged,
+ stats->dispatched, atomic_read(&stats->completed));
}
- free_percpu(dd->stats);
-
kfree(dd);
}
@@ -578,11 +558,6 @@ static int dd_init_sched(struct request_queue *q, struct elevator_type *e)
eq->elevator_data = dd;
- dd->stats = alloc_percpu_gfp(typeof(*dd->stats),
- GFP_KERNEL | __GFP_ZERO);
- if (!dd->stats)
- goto free_dd;
-
for (prio = 0; prio <= DD_PRIO_MAX; prio++) {
struct dd_per_prio *per_prio = &dd->per_prio[prio];
@@ -604,9 +579,6 @@ static int dd_init_sched(struct request_queue *q, struct elevator_type *e)
q->elevator = eq;
return 0;
-free_dd:
- kfree(dd);
-
put_eq:
kobject_put(&eq->kobj);
return ret;
@@ -689,8 +661,9 @@ static void dd_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq,
blk_req_zone_write_unlock(rq);
prio = ioprio_class_to_prio[ioprio_class];
+ per_prio = &dd->per_prio[prio];
if (!rq->elv.priv[0]) {
- dd_count(dd, inserted, prio);
+ per_prio->stats.inserted++;
rq->elv.priv[0] = (void *)(uintptr_t)1;
}
@@ -701,7 +674,6 @@ static void dd_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq,
trace_block_rq_insert(rq);
- per_prio = &dd->per_prio[prio];
if (at_head) {
list_add(&rq->queuelist, &per_prio->dispatch);
} else {
@@ -779,7 +751,7 @@ static void dd_finish_request(struct request *rq)
if (!rq->elv.priv[0])
return;
- dd_count(dd, completed, prio);
+ atomic_inc(&per_prio->stats.completed);
if (blk_queue_is_zoned(q)) {
unsigned long flags;
@@ -966,28 +938,44 @@ static int dd_queued_show(void *data, struct seq_file *m)
{
struct request_queue *q = data;
struct deadline_data *dd = q->elevator->elevator_data;
+ u32 rt, be, idle;
+
+ spin_lock(&dd->lock);
+ rt = dd_queued(dd, DD_RT_PRIO);
+ be = dd_queued(dd, DD_BE_PRIO);
+ idle = dd_queued(dd, DD_IDLE_PRIO);
+ spin_unlock(&dd->lock);
+
+ seq_printf(m, "%u %u %u\n", rt, be, idle);
- seq_printf(m, "%u %u %u\n", dd_queued(dd, DD_RT_PRIO),
- dd_queued(dd, DD_BE_PRIO),
- dd_queued(dd, DD_IDLE_PRIO));
return 0;
}
/* Number of requests owned by the block driver for a given priority. */
static u32 dd_owned_by_driver(struct deadline_data *dd, enum dd_prio prio)
{
- return dd_sum(dd, dispatched, prio) + dd_sum(dd, merged, prio)
- - dd_sum(dd, completed, prio);
+ const struct io_stats_per_prio *stats = &dd->per_prio[prio].stats;
+
+ lockdep_assert_held(&dd->lock);
+
+ return stats->dispatched + stats->merged -
+ atomic_read(&stats->completed);
}
static int dd_owned_by_driver_show(void *data, struct seq_file *m)
{
struct request_queue *q = data;
struct deadline_data *dd = q->elevator->elevator_data;
+ u32 rt, be, idle;
+
+ spin_lock(&dd->lock);
+ rt = dd_owned_by_driver(dd, DD_RT_PRIO);
+ be = dd_owned_by_driver(dd, DD_BE_PRIO);
+ idle = dd_owned_by_driver(dd, DD_IDLE_PRIO);
+ spin_unlock(&dd->lock);
+
+ seq_printf(m, "%u %u %u\n", rt, be, idle);
- seq_printf(m, "%u %u %u\n", dd_owned_by_driver(dd, DD_RT_PRIO),
- dd_owned_by_driver(dd, DD_BE_PRIO),
- dd_owned_by_driver(dd, DD_IDLE_PRIO));
return 0;
}
--
2.35.3