linux-kernel - [PATCH] block: allow specifying default iosched in config

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Date:   Mon, 26 Sep 2022 15:01:34 -0700
From:   Khazhismel Kumykov <khazhy@...omium.org>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        Khazhismel Kumykov <khazhy@...gle.com>
Subject: [PATCH] block: allow specifying default iosched in config

Setting IO scheduler at device init time in kernel is useful, and moving
this option into kernel config makes it possible to build different
kernels with different default schedulers from the same tree.

Order deadline->none->rest to retain current behavior of using "none" by
default if mq-deadline is not enabled.

Signed-off-by: Khazhismel Kumykov <khazhy@...gle.com>
---
checkpatch suggested more verbose help descriptions, but I felt it'd be
too much repeated from the main config options, so opted to leave them
out.

 block/Kconfig.iosched | 28 ++++++++++++++++++++++++++++
 block/elevator.c      |  2 +-
 2 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/block/Kconfig.iosched b/block/Kconfig.iosched
index 615516146086..38a83282802a 100644
--- a/block/Kconfig.iosched
+++ b/block/Kconfig.iosched
@@ -43,4 +43,32 @@ config BFQ_CGROUP_DEBUG
 	Enable some debugging help. Currently it exports additional stat
 	files in a cgroup which can be useful for debugging.
 
+choice
+	prompt "Default I/O scheduler"
+	default DEFAULT_MQ_DEADLINE
+	help
+	  Select the I/O scheduler which will be used by default for block devices
+	  with a single hardware queue.
+
+config DEFAULT_MQ_DEADLINE
+	bool "MQ Deadline" if MQ_IOSCHED_DEADLINE=y
+
+config DEFAULT_NONE
+	bool "none"
+
+config DEFAULT_MQ_KYBER
+	bool "Kyber" if MQ_IOSCHED_KYBER=y
+
+config DEFAULT_BFQ
+	bool "BFQ" if IOSCHED_BFQ=y
+
+endchoice
+
+config MQ_DEFAULT_IOSCHED
+	string
+	default "mq-deadline" if DEFAULT_MQ_DEADLINE
+	default "none" if DEFAULT_NONE
+	default "kyber" if DEFAULT_MQ_KYBER
+	default "bfq" if DEFAULT_BFQ
+
 endmenu
diff --git a/block/elevator.c b/block/elevator.c
index c319765892bb..4137933dfd16 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -642,7 +642,7 @@ static struct elevator_type *elevator_get_default(struct request_queue *q)
 	    !blk_mq_is_shared_tags(q->tag_set->flags))
 		return NULL;
 
-	return elevator_get(q, "mq-deadline", false);
+	return elevator_get(q, CONFIG_MQ_DEFAULT_IOSCHED, false);
 }
 
 /*
-- 
2.37.3.998.g577e59143f-goog