Re: [PATCH -next RFC 1/6] blk-mq: add a new flag 'BLK_MQ_F_NO_TAG_PREEMPTION'

[Jens Axboe]

On 3/29/22 3:40 AM, Yu Kuai wrote:
> Tag preemption is the default behaviour, specifically blk_mq_get_tag()
> will try to get tag unconditionally, which means a new io can preempt tag
> even if there are lots of ios that are waiting for tags.
> 
> This patch introduce a new flag, prepare to disable such behaviour, in
> order to optimize io performance for large random io for HHD.

Not sure why we need a flag for this behavior. Does it ever make sense
to allow preempting waiters, jumping the queue?

-- 
Jens Axboe