Messages in this thread | | | Subject | Re: [PATCH -next RFC v2 2/8] blk-mq: call 'bt_wait_ptr()' later in blk_mq_get_tag() | From | "yukuai (C)" <> | Date | Sat, 9 Apr 2022 10:09:52 +0800 |
| |
在 2022/04/08 22:20, Bart Van Assche 写道: > On 4/8/22 00:39, Yu Kuai wrote: >> bt_wait_ptr() will increase 'wait_index', however, if blk_mq_get_tag() >> get a tag successfully after bt_wait_ptr() is called and before >> sbitmap_prepare_to_wait() is called, then the 'ws' is skipped. This >> behavior might cause 8 waitqueues to be unbalanced. >> >> Move bt_wait_ptr() later should reduce the problem when the disk is >> under high io preesure. >> >> Signed-off-by: Yu Kuai <yukuai3@huawei.com> >> --- >> block/blk-mq-tag.c | 4 +--- >> 1 file changed, 1 insertion(+), 3 deletions(-) >> >> diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c >> index 68ac23d0b640..228a0001694f 100644 >> --- a/block/blk-mq-tag.c >> +++ b/block/blk-mq-tag.c >> @@ -155,7 +155,6 @@ unsigned int blk_mq_get_tag(struct >> blk_mq_alloc_data *data) >> if (data->flags & BLK_MQ_REQ_NOWAIT) >> return BLK_MQ_NO_TAG; >> - ws = bt_wait_ptr(bt, data->hctx); >> do { >> struct sbitmap_queue *bt_prev; >> @@ -174,6 +173,7 @@ unsigned int blk_mq_get_tag(struct >> blk_mq_alloc_data *data) >> if (tag != BLK_MQ_NO_TAG) >> break; >> + ws = bt_wait_ptr(bt, data->hctx); >> sbitmap_prepare_to_wait(bt, ws, &wait, TASK_UNINTERRUPTIBLE); >> tag = __blk_mq_get_tag(data, bt); >> @@ -201,8 +201,6 @@ unsigned int blk_mq_get_tag(struct >> blk_mq_alloc_data *data) >> */ >> if (bt != bt_prev) >> sbitmap_queue_wake_up(bt_prev); >> - >> - ws = bt_wait_ptr(bt, data->hctx); >> } while (1); > > Is it necessary to call bt_wait_ptr() during every loop iteration or > only if bt != bt_prev? Would calling bt_wait_ptr() only if bt != bt_prev > help to reduce unfairness further? Hi,
You are right, that sounds reasonable.
Thanks, Kuai > > Thanks, > > Bart. > . >
| |