linux-kernel - [PATCH 1/4] blk-mq: use percpu csd to remote complete instead of per-rq csd

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Date:   Tue, 27 Jun 2023 20:08:51 +0800
From:   chengming.zhou@...ux.dev
To:     axboe@...nel.dk, tj@...nel.org, hch@....de, ming.lei@...hat.com
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        zhouchengming@...edance.com
Subject: [PATCH 1/4] blk-mq: use percpu csd to remote complete instead of per-rq csd

From: Chengming Zhou <zhouchengming@...edance.com>

If request need to be completed remotely, we insert it into percpu llist,
and smp_call_function_single_async() if llist is empty previously.

We don't need to use per-rq csd, percpu csd is enough. And the size of
struct request is decreased by 24 bytes.

Signed-off-by: Chengming Zhou <zhouchengming@...edance.com>
---
 block/blk-mq.c         | 12 ++++++++----
 include/linux/blk-mq.h |  5 +----
 2 files changed, 9 insertions(+), 8 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index decb6ab2d508..a36822479b94 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -43,6 +43,7 @@
 #include "blk-ioprio.h"
 
 static DEFINE_PER_CPU(struct llist_head, blk_cpu_done);
+static DEFINE_PER_CPU(struct __call_single_data, blk_cpu_csd);
 
 static void blk_mq_insert_request(struct request *rq, blk_insert_t flags);
 static void blk_mq_request_bypass_insert(struct request *rq,
@@ -1156,13 +1157,13 @@ static void blk_mq_complete_send_ipi(struct request *rq)
 {
 	struct llist_head *list;
 	unsigned int cpu;
+	struct __call_single_data *csd;
 
 	cpu = rq->mq_ctx->cpu;
 	list = &per_cpu(blk_cpu_done, cpu);
-	if (llist_add(&rq->ipi_list, list)) {
-		INIT_CSD(&rq->csd, __blk_mq_complete_request_remote, rq);
-		smp_call_function_single_async(cpu, &rq->csd);
-	}
+	csd = &per_cpu(blk_cpu_csd, cpu);
+	if (llist_add(&rq->ipi_list, list))
+		smp_call_function_single_async(cpu, csd);
 }
 
 static void blk_mq_raise_softirq(struct request *rq)
@@ -4796,6 +4797,9 @@ static int __init blk_mq_init(void)
 
 	for_each_possible_cpu(i)
 		init_llist_head(&per_cpu(blk_cpu_done, i));
+	for_each_possible_cpu(i)
+		INIT_CSD(&per_cpu(blk_cpu_csd, i),
+			 __blk_mq_complete_request_remote, NULL);
 	open_softirq(BLOCK_SOFTIRQ, blk_done_softirq);
 
 	cpuhp_setup_state_nocalls(CPUHP_BLOCK_SOFTIRQ_DEAD,
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index f401067ac03a..070551197c0e 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -182,10 +182,7 @@ struct request {
 		rq_end_io_fn		*saved_end_io;
 	} flush;
 
-	union {
-		struct __call_single_data csd;
-		u64 fifo_time;
-	};
+	u64 fifo_time;
 
 	/*
 	 * completion callback.
-- 
2.39.2