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

From: Christoph Hellwig
Date: Wed Jun 04 2014 - 11:05:18 EST

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.

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

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