Re: [PATCH V2 2/2] blk-mq: make sure elevator callbacks aren't called for passthrough request

[Ming Lei <ming.lei@redhat.com>]

On Wed, May 17, 2023 at 09:22:18AM +0200, Christoph Hellwig wrote:
> On Tue, May 16, 2023 at 04:39:05PM +0800, Ming Lei wrote:
> > I can understand the point, but it may not be done by single flag,
> 
> Can you explain why?  Note that we also already have RQF_ELVPRIV for
> any request that has elevator private data.  I don't really think we
> need a third flag.

RQF_ELVPRIV isn't same with RQF_ELV, and follows the two's relationship:

	RQF_ELVPRIV == (RQF_ELV && non_flush_pt_req && !e->type->ops.prepare_request)

RQF_ELVPRIV can be replaced with the above expression to save one flag.

RQF_ELV isn't same with RQF_SCHED_TAGS too, RQF_ELV should be used for
checking if elevator callback is needed, and RQF_SCHED_TAGS is for allocating
req/tag and dealing with tags busy things.

In case of q->elevator, RQF_SCHED_TAGS is always set, but

- for pt/flush request, RQF_ELV is cleared.
- for other request, RQF_ELV are set

Then we can avoid any elevator callback for pt/flush request.


thanks, 
Ming