From 90b7198001f23ea37d3b46dc631bdaa2357a20b1 Mon Sep 17 00:00:00 2001 From: Bart Van Assche Date: Thu, 5 Aug 2021 10:41:59 -0700 Subject: [PATCH] blk-mq: Introduce the BLK_MQ_F_NO_SCHED_BY_DEFAULT flag elevator_get_default() uses the following algorithm to select an I/O scheduler from inside add_disk(): - In case of a single hardware queue or if sharing hardware queues across multiple request queues (BLK_MQ_F_TAG_HCTX_SHARED), use mq-deadline. - Otherwise, use 'none'. This is a good choice for most but not for all block drivers. Make it possible to override the selection of mq-deadline with a new flag, namely BLK_MQ_F_NO_SCHED_BY_DEFAULT. Cc: Christoph Hellwig Cc: Ming Lei Cc: Tetsuo Handa Cc: Martijn Coenen Cc: Jaegeuk Kim Signed-off-by: Bart Van Assche Link: https://lore.kernel.org/r/20210805174200.3250718-2-bvanassche@acm.org Signed-off-by: Jens Axboe --- block/elevator.c | 3 +++ include/linux/blk-mq.h | 6 ++++++ 2 files changed, 9 insertions(+) diff --git a/block/elevator.c b/block/elevator.c index 52ada14cfe45..d0295e68f481 100644 --- a/block/elevator.c +++ b/block/elevator.c @@ -630,6 +630,9 @@ static inline bool elv_support_iosched(struct request_queue *q) */ static struct elevator_type *elevator_get_default(struct request_queue *q) { + if (q->tag_set && q->tag_set->flags & BLK_MQ_F_NO_SCHED_BY_DEFAULT) + return NULL; + if (q->nr_hw_queues != 1 && !blk_mq_is_sbitmap_shared(q->tag_set->flags)) return NULL; diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h index 1d18447ebebc..22215db36122 100644 --- a/include/linux/blk-mq.h +++ b/include/linux/blk-mq.h @@ -404,7 +404,13 @@ enum { BLK_MQ_F_STACKING = 1 << 2, BLK_MQ_F_TAG_HCTX_SHARED = 1 << 3, BLK_MQ_F_BLOCKING = 1 << 5, + /* Do not allow an I/O scheduler to be configured. */ BLK_MQ_F_NO_SCHED = 1 << 6, + /* + * Select 'none' during queue registration in case of a single hwq + * or shared hwqs instead of 'mq-deadline'. + */ + BLK_MQ_F_NO_SCHED_BY_DEFAULT = 1 << 7, BLK_MQ_F_ALLOC_POLICY_START_BIT = 8, BLK_MQ_F_ALLOC_POLICY_BITS = 1,