Re: [RFD] I/O scheduling in blk-mq

[Bart Van Assche <bvanassche@acm.org>]

On 08/08/16 07:09, Paolo wrote:
> 2) To provide per-process service guarantees, an I/O scheduler must
> create per-process internal queues. BFQ and CFQ use I/O contexts to
> achieve this goal. Is something like that (or exactly the same)
> available also in blk-mq? If so, do you have any suggestion, or link to
> documentation/code on how to use what is available in blk-mq?

Hello Paolo,

I/O contexts are, by definition, data structures that are shared by 
multiple I/O queues. blk-mq reaches high performance by keeping each 
per-CPU queue independent. This means that using I/O contexts in a 
blk-mq I/O scheduler would introduce a contention point and probably 
also a performance bottleneck. So I would appreciate it if multiqueue 
schedulers would avoid constructs similar to I/O contexts.

Thanks,

Bart.