From: Omar Sandoval <osandov@xxxxxx>
Allocating your own per-cpu allocation hint separately makes for an
awkward API. Instead, allocate the per-cpu hint as part of the `struct
scale_bitmap_queue`. There's no point for a `struct scale_bitmap_queue`
without the cache, but you can still use a bare `struct scale_bitmap`.
Signed-off-by: Omar Sandoval <osandov@xxxxxx>
---
block/blk-mq-tag.c | 40 ++++++++++++++++-------------------
block/blk-mq-tag.h | 3 ++-
block/blk-mq.c | 2 +-
block/blk-mq.h | 2 --
include/linux/scale_bitmap.h | 50 +++++++++++++++++++++++++++++++++++++++++++-
lib/scale_bitmap.c | 16 ++++++++++++--
6 files changed, 84 insertions(+), 29 deletions(-)
diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index 22eae05..cc1941b 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -94,23 +94,21 @@ static inline bool hctx_may_queue(struct blk_mq_hw_ctx *hctx,
#define BT_ALLOC_RR(tags) (tags->alloc_policy == BLK_TAG_ALLOC_RR)
static int __bt_get(struct blk_mq_hw_ctx *hctx, struct scale_bitmap_queue *bt,
- unsigned int *tag_cache, struct blk_mq_tags *tags)
+ struct blk_mq_tags *tags)
{
if (!hctx_may_queue(hctx, bt))
return -1;
- return scale_bitmap_get(&bt->map, tag_cache, BT_ALLOC_RR(tags));
+ return __scale_bitmap_queue_get(bt, BT_ALLOC_RR(tags));
}
-static int bt_get(struct blk_mq_alloc_data *data,
- struct scale_bitmap_queue *bt,
- struct blk_mq_hw_ctx *hctx,
- unsigned int *last_tag, struct blk_mq_tags *tags)
+static int bt_get(struct blk_mq_alloc_data *data, struct scale_bitmap_queue *bt,
+ struct blk_mq_hw_ctx *hctx, struct blk_mq_tags *tags)
{
struct sbq_wait_state *ws;
DEFINE_WAIT(wait);
int tag;
- tag = __bt_get(hctx, bt, last_tag, tags);
+ tag = __bt_get(hctx, bt, tags);
if (tag != -1)
return tag;
@@ -121,7 +119,7 @@ static int bt_get(struct blk_mq_alloc_data *data,
do {
prepare_to_wait(&ws->wait, &wait, TASK_UNINTERRUPTIBLE);
- tag = __bt_get(hctx, bt, last_tag, tags);
+ tag = __bt_get(hctx, bt, tags);
if (tag != -1)
break;
@@ -138,7 +136,7 @@ static int bt_get(struct blk_mq_alloc_data *data,
* Retry tag allocation after running the hardware queue,
* as running the queue may also have found completions.
*/
- tag = __bt_get(hctx, bt, last_tag, tags);
+ tag = __bt_get(hctx, bt, tags);
if (tag != -1)
break;
@@ -152,7 +150,6 @@ static int bt_get(struct blk_mq_alloc_data *data,
if (data->flags & BLK_MQ_REQ_RESERVED) {
bt = &data->hctx->tags->breserved_tags;
} else {
- last_tag = &data->ctx->last_tag;
hctx = data->hctx;
bt = &hctx->tags->bitmap_tags;
}
@@ -169,7 +166,7 @@ static unsigned int __blk_mq_get_tag(struct blk_mq_alloc_data *data)
int tag;
tag = bt_get(data, &data->hctx->tags->bitmap_tags, data->hctx,
- &data->ctx->last_tag, data->hctx->tags);
+ data->hctx->tags);
if (tag >= 0)
return tag + data->hctx->tags->nr_reserved_tags;
@@ -178,15 +175,15 @@ static unsigned int __blk_mq_get_tag(struct blk_mq_alloc_data *data)
static unsigned int __blk_mq_get_reserved_tag(struct blk_mq_alloc_data *data)
{
- int tag, zero = 0;
+ int tag;
if (unlikely(!data->hctx->tags->nr_reserved_tags)) {
WARN_ON_ONCE(1);
return BLK_MQ_TAG_FAIL;
}
- tag = bt_get(data, &data->hctx->tags->breserved_tags, NULL, &zero,
- data->hctx->tags);
+ tag = bt_get(data, &data->hctx->tags->breserved_tags, NULL,
+ data->hctx->tags);
if (tag < 0)
return BLK_MQ_TAG_FAIL;
@@ -200,8 +197,8 @@ unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data)
return __blk_mq_get_tag(data);
}
-void blk_mq_put_tag(struct blk_mq_hw_ctx *hctx, unsigned int tag,
- unsigned int *last_tag)
+void blk_mq_put_tag(struct blk_mq_hw_ctx *hctx, struct blk_mq_ctx *ctx,
+ unsigned int tag)
{
struct blk_mq_tags *tags = hctx->tags;
@@ -209,12 +206,12 @@ void blk_mq_put_tag(struct blk_mq_hw_ctx *hctx, unsigned int tag,
const int real_tag = tag - tags->nr_reserved_tags;
BUG_ON(real_tag >= tags->nr_tags);
- scale_bitmap_queue_clear(&tags->bitmap_tags, real_tag);
- if (likely(tags->alloc_policy == BLK_TAG_ALLOC_FIFO))
- *last_tag = real_tag;
+ scale_bitmap_queue_clear(&tags->bitmap_tags, real_tag,
+ BT_ALLOC_RR(tags), ctx->cpu);
} else {
BUG_ON(tag >= tags->nr_reserved_tags);
- scale_bitmap_queue_clear(&tags->breserved_tags, tag);
+ scale_bitmap_queue_clear(&tags->breserved_tags, tag,
+ BT_ALLOC_RR(tags), ctx->cpu);
}
}
@@ -369,8 +366,7 @@ static unsigned int bt_unused_tags(const struct scale_bitmap_queue *bt)
return bt->map.depth - scale_bitmap_weight(&bt->map);
}
-static int bt_alloc(struct scale_bitmap_queue *bt, unsigned int depth,
- int node)
+static int bt_alloc(struct scale_bitmap_queue *bt, unsigned int depth, int node)
{
return scale_bitmap_queue_init_node(bt, depth, -1, GFP_KERNEL, node);
}
diff --git a/block/blk-mq-tag.h b/block/blk-mq-tag.h
index 1277f24..d52c286 100644
--- a/block/blk-mq-tag.h
+++ b/block/blk-mq-tag.h
@@ -27,7 +27,8 @@ extern struct blk_mq_tags *blk_mq_init_tags(unsigned int nr_tags, unsigned int r
extern void blk_mq_free_tags(struct blk_mq_tags *tags);
extern unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data);
-extern void blk_mq_put_tag(struct blk_mq_hw_ctx *hctx, unsigned int tag, unsigned int *last_tag);
+extern void blk_mq_put_tag(struct blk_mq_hw_ctx *hctx, struct blk_mq_ctx *ctx,
+ unsigned int tag);
extern bool blk_mq_has_free_tags(struct blk_mq_tags *tags);
extern ssize_t blk_mq_tag_sysfs_show(struct blk_mq_tags *tags, char *page);
extern void blk_mq_tag_init_last_tag(struct blk_mq_tags *tags, unsigned int *last_tag);
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 7229300..e14ab9e 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -302,7 +302,7 @@ static void __blk_mq_free_request(struct blk_mq_hw_ctx *hctx,
rq->cmd_flags = 0;
clear_bit(REQ_ATOM_STARTED, &rq->atomic_flags);
- blk_mq_put_tag(hctx, tag, &ctx->last_tag);
+ blk_mq_put_tag(hctx, ctx, tag);
blk_queue_exit(q);
}
diff --git a/block/blk-mq.h b/block/blk-mq.h
index 71831f9..9b15d2e 100644
--- a/block/blk-mq.h
+++ b/block/blk-mq.h
@@ -12,8 +12,6 @@ struct blk_mq_ctx {
unsigned int cpu;
unsigned int index_hw;
- unsigned int last_tag ____cacheline_aligned_in_smp;
-
/* incremented at dispatch time */
unsigned long rq_dispatched[2];
unsigned long rq_merged;
diff --git a/include/linux/scale_bitmap.h b/include/linux/scale_bitmap.h
index 63f712b..49824c1 100644
--- a/include/linux/scale_bitmap.h
+++ b/include/linux/scale_bitmap.h
@@ -99,6 +99,14 @@ struct scale_bitmap_queue {
*/
struct scale_bitmap map;
+ /*
+ * @alloc_hint: Cache of last successfully allocated or freed bit.
+ *
+ * This is per-cpu, which allows multiple users to stick to different
+ * cachelines until the map is exhausted.
+ */
+ unsigned int __percpu *alloc_hint;
+
/**
* @wake_batch: Number of bits which must be freed before we wake up any
* waiters.
@@ -279,6 +287,7 @@ int scale_bitmap_queue_init_node(struct scale_bitmap_queue *sbq,
static inline void scale_bitmap_queue_free(struct scale_bitmap_queue *sbq)
{
kfree(sbq->ws);
+ free_percpu(sbq->alloc_hint);
scale_bitmap_free(&sbq->map);
}
@@ -295,12 +304,51 @@ void scale_bitmap_queue_resize(struct scale_bitmap_queue *sbq,
unsigned int depth);
/**
+ * __scale_bitmap_queue_get() - Try to allocate a free bit from a &struct
+ * scale_bitmap_queue with preemption already disabled.
+ * @sbq: Bitmap queue to allocate from.
+ * @round_robin: See scale_bitmap_get().
+ *
+ * Return: Non-negative allocated bit number if successful, -1 otherwise.
+ */
+static inline int __scale_bitmap_queue_get(struct scale_bitmap_queue *sbq,
+ bool round_robin)
+{
+ return scale_bitmap_get(&sbq->map, this_cpu_ptr(sbq->alloc_hint),
+ round_robin);
+}
+
+/**
+ * scale_bitmap_queue_get() - Try to allocate a free bit from a &struct
+ * scale_bitmap_queue.
+ * @sbq: Bitmap queue to allocate from.
+ * @round_robin: See scale_bitmap_get().
+ * @cpu: Output parameter; will contain the CPU we ran on (e.g., to be passed to
+ * scale_bitmap_queue_clear()).
+ *
+ * Return: Non-negative allocated bit number if successful, -1 otherwise.
+ */
+static inline int scale_bitmap_queue_get(struct scale_bitmap_queue *sbq,
+ bool round_robin, unsigned int *cpu)
+{
+ int ret;
+
+ *cpu = get_cpu();
+ ret = __scale_bitmap_queue_get(sbq, round_robin);
+ put_cpu();
+ return ret;
+}
+
+/**
* scale_bitmap_queue_clear() - Free an allocated bit and wake up waiters on a
* &struct scale_bitmap_queue.
* @sbq: Bitmap to free from.
* @nr: Bit number to free.
+ * @round_robin: See scale_bitmap_get().
+ * @cpu: CPU the bit was allocated on.
*/
-void scale_bitmap_queue_clear(struct scale_bitmap_queue *sbq, unsigned int nr);
+void scale_bitmap_queue_clear(struct scale_bitmap_queue *sbq, unsigned int nr,
+ bool round_robin, unsigned int cpu);
static inline int sbq_index_inc(int index)
{
diff --git a/lib/scale_bitmap.c b/lib/scale_bitmap.c
index 237170c..12fee62 100644
--- a/lib/scale_bitmap.c
+++ b/lib/scale_bitmap.c
@@ -206,6 +206,12 @@ int scale_bitmap_queue_init_node(struct scale_bitmap_queue *sbq,
if (ret)
return ret;
+ sbq->alloc_hint = alloc_percpu_gfp(unsigned int, flags);
+ if (!sbq->alloc_hint) {
+ scale_bitmap_free(&sbq->map);
+ return -ENOMEM;
+ }
+
sbq->wake_batch = SBQ_WAKE_BATCH;
if (sbq->wake_batch > depth / SBQ_WAIT_QUEUES)
sbq->wake_batch = max(1U, depth / SBQ_WAIT_QUEUES);
@@ -214,6 +220,7 @@ int scale_bitmap_queue_init_node(struct scale_bitmap_queue *sbq,
sbq->ws = kzalloc_node(SBQ_WAIT_QUEUES * sizeof(*sbq->ws), flags, node);
if (!sbq->ws) {
+ free_percpu(sbq->alloc_hint);
scale_bitmap_free(&sbq->map);
return -ENOMEM;
}
@@ -259,7 +266,8 @@ static struct sbq_wait_state *sbq_wake_ptr(struct scale_bitmap_queue *sbq)
return NULL;
}
-void scale_bitmap_queue_clear(struct scale_bitmap_queue *sbq, unsigned int nr)
+void scale_bitmap_queue_clear(struct scale_bitmap_queue *sbq, unsigned int nr,
+ bool round_robin, unsigned int cpu)
{
struct sbq_wait_state *ws;
int wait_cnt;
@@ -271,7 +279,7 @@ void scale_bitmap_queue_clear(struct scale_bitmap_queue *sbq, unsigned int nr)
ws = sbq_wake_ptr(sbq);
if (!ws)
- return;
+ goto update_cache;
wait_cnt = atomic_dec_return(&ws->wait_cnt);
if (unlikely(wait_cnt < 0))
@@ -281,6 +289,10 @@ void scale_bitmap_queue_clear(struct scale_bitmap_queue *sbq, unsigned int nr)
sbq_index_atomic_inc(&sbq->wake_index);
wake_up(&ws->wait);
}
+
+update_cache:
+ if (likely(!round_robin))
+ *per_cpu_ptr(sbq->alloc_hint, cpu) = nr;
}
EXPORT_SYMBOL_GPL(scale_bitmap_queue_clear);
--
2.9.3
--
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