Re: [patch]blk-mq: blk_mq_tag_to_rq should handle flush request

[Jens Axboe <axboe@kernel.dk>]

On 2014-06-04 09:05, Christoph Hellwig wrote:
> On Wed, Jun 04, 2014 at 09:02:19AM -0600, Jens Axboe wrote:
>> OK strange, there hasn't been that much churn since the last rebase.
>> In my for-linus, there's a patch for a single queue crash, but that
>> should just hit for the removal case. And then there's the atomic
>> schedule patch, but that issue was actually in the code base for
>> about a month, so not a new one either.
>
> You're request initializaion optimization doesn't set up req->cmd and
> thus causes all BLOCK_PC I/O (including the SCSI LUN scan) to crash and
> burn.  The trivial fix is on your way.

OK. That'll arguably be a good cleanup as well, getting that initialized 
in the right place. I hate the 'lets clear all the memory' part of rq 
init, it's not super cheap to do.

> The performance regression is caused by "blk-mq: avoid code
> duplication", but I don't really understand why yet.

Gah, looks like this one dropped the tag idling. I bet that is why.


-- 
Jens Axboe