Re: calling scsi_adjust_queue_depth() during I/O...

[James Bottomley <James.Bottomley@SteelEye.com>]

On Fri, 2005-08-05 at 21:33 +0900, Tejun Heo wrote:
>  Here's the fix.  It basically revives bqt->real_max_depth sans
> allocation optimization in init_tag_map.  I've also added a comment
> explicitly noting that tag map cannot be shrunk to prevent other
> morons like me.  :-( Please try this one and let me know how it works.
> If this is the correct fix, I'll repost properly to Jens and lkml with
> detailed explanation on how it was broken in the original code and how
> I broke it with my previous patch.  Sorry.

Actually, if you really want to adjust the array size downwards, there's
a way we can do it:

- If the bits that would be lost on shrinkage are all zero at the time
blk_queue_resize_tags() is called, that means that there are no
outstanding tags up there and the array can be shrunk immediately.

- If there are outstanding tags between the new and the old depth, the
array can be shrunk when the last one of these returns, say in
blk_rq_end_tag()

James