Re: [PATCH V2 0/2] block: remove unnecessary RESTART

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

On Wed, Nov 01, 2017 at 05:09:41PM +0000, Bart Van Assche wrote:
> On Thu, 2017-11-02 at 00:59 +0800, Ming Lei wrote:
> > The commit has described clearly that we don't need to iterate over all hw
> > queue when completing an I/O.
> 
> You quoted a small part of the description of commit da55f2cc7841 and left out
> the part that shows that what you wrote above is not correct.

If you mean the 1st part:

    Commit 50e1dab86aa2 ("blk-mq-sched: fix starvation for multiple hardware
    queues and shared tags") fixed one starvation issue for shared tags.
    However, we can still get into a situation where we fail to allocate a
    tag because all tags are allocated but we don't have any pending
    requests on any hardware queue.

That is just what this commit wants to address, then we don't need to
depend on restart from all hctx for fixing this starvation.

If you don't believe me, you can ask Omar and Jens to clarify.

-- 
Ming