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FROMGIT: blk-mq: Introduce the BLK_MQ_F_NO_SCHED_BY_DEFAULT flag

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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 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.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Bug: 194450129
(cherry picked from commit 90b7198001f23ea37d3b46dc631bdaa2357a20b1 git://git.kernel.dk/linux-block/ for-5.15/block)
Change-Id: I4fb658957c193f350e74bdb5876c20a8f628fcb1
Signed-off-by: Bart Van Assche <bvanassche@google.com>
This commit is contained in:
Bart Van Assche 2021-08-03 09:15:12 -07:00 committed by Bart Van Assche
parent 8914725a58
commit d8b946254e
2 changed files with 9 additions and 0 deletions
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3
block/elevator.c
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@ -621,6 +621,9 @@ 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)
return NULL;

6
include/linux/blk-mq.h
View File

@ -394,7 +394,13 @@ 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,