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

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On 2022/03/29 20:44, Jens Axboe wrote:
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?


Hi,

I was thinking using the flag to control the new behavior, in order to
reduce the impact on general path.

If wake up path is handled properly, I think it's ok to disable
preempting tags.

Thanks
Kuai



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