[PATCH 1/6] blk-mq: allocate request on cpu in hctx->cpumask for blk_mq_alloc_request_hctx

[Ming Lei <ming.lei@xxxxxxxxxx>]

blk_mq_alloc_request_hctx() asks blk-mq to allocate request from
specified hctx, which is usually bound with fixed cpu mapping, and
request is supposed to be allocated on CPU in hctx->cpumask.

So use smp_call_function_any() to allocate request on the cpu in
hctx->cpumask for blk_mq_alloc_request_hctx().

Dedclare blk_mq_get_request() beforehand because the following patches
reuses __blk_mq_alloc_request for blk_mq_get_request().

Prepare for improving cpu hotplug support.

Cc: Bart Van Assche <bvanassche@xxxxxxx>
Cc: Hannes Reinecke <hare@xxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: John Garry <john.garry@xxxxxxxxxx>
Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
---
 block/blk-mq.c | 35 ++++++++++++++++++++++++++---------
 1 file changed, 26 insertions(+), 9 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 9ee695bdf873..e2e1b6808b32 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -40,6 +40,10 @@
 #include "blk-mq-sched.h"
 #include "blk-rq-qos.h"
 
+static struct request *blk_mq_get_request(struct request_queue *q,
+					  struct bio *bio,
+					  struct blk_mq_alloc_data *data);
+
 static void blk_mq_poll_stats_start(struct request_queue *q);
 static void blk_mq_poll_stats_fn(struct blk_stat_callback *cb);
 
@@ -330,6 +334,19 @@ static struct request *blk_mq_rq_ctx_init(struct blk_mq_alloc_data *data,
 	return rq;
 }
 
+struct blk_mq_smp_call_info {
+	struct request_queue *q;
+	struct blk_mq_alloc_data *data;
+	struct request *rq;
+};
+
+static void __blk_mq_alloc_request(void *alloc_info)
+{
+	struct blk_mq_smp_call_info *info = alloc_info;
+
+	info->rq = blk_mq_get_request(info->q, NULL, info->data);
+}
+
 static struct request *blk_mq_get_request(struct request_queue *q,
 					  struct bio *bio,
 					  struct blk_mq_alloc_data *data)
@@ -424,8 +441,7 @@ struct request *blk_mq_alloc_request_hctx(struct request_queue *q,
 	unsigned int op, blk_mq_req_flags_t flags, unsigned int hctx_idx)
 {
 	struct blk_mq_alloc_data alloc_data = { .flags = flags, .cmd_flags = op };
-	struct request *rq;
-	unsigned int cpu;
+	struct blk_mq_smp_call_info info = {.q = q, .data = &alloc_data};
 	int ret;
 
 	/*
@@ -448,21 +464,22 @@ struct request *blk_mq_alloc_request_hctx(struct request_queue *q,
 	 * Check if the hardware context is actually mapped to anything.
 	 * If not tell the caller that it should skip this queue.
 	 */
-	alloc_data.hctx = q->queue_hw_ctx[hctx_idx];
-	if (!blk_mq_hw_queue_mapped(alloc_data.hctx)) {
+	if (!blk_mq_hw_queue_mapped(q->queue_hw_ctx[hctx_idx])) {
 		blk_queue_exit(q);
 		return ERR_PTR(-EXDEV);
 	}
-	cpu = cpumask_first_and(alloc_data.hctx->cpumask, cpu_online_mask);
-	alloc_data.ctx = __blk_mq_get_ctx(q, cpu);
 
-	rq = blk_mq_get_request(q, NULL, &alloc_data);
+	ret = smp_call_function_any(alloc_data.hctx->cpumask,
+			__blk_mq_alloc_request, &info, 1);
 	blk_queue_exit(q);
 
-	if (!rq)
+	if (ret)
+		return ERR_PTR(ret);
+
+	if (!info.rq)
 		return ERR_PTR(-EWOULDBLOCK);
 
-	return rq;
+	return info.rq;
 }
 EXPORT_SYMBOL_GPL(blk_mq_alloc_request_hctx);
 
-- 
2.25.2