Re: [Xen-devel] blkif sort queue

Keir Fraser
Sun, 10 Oct 2004 09:27:26 -0000

The scheduling in the frontend domain probably doesn''t buy us very
much as the backend will do its own scheduling, and has a better idea
about the mapping of block addresses onto spindles.
However, the extra overhead is not going to hurt our disc
performance.

 -- Keir


> Hi, I''m one of the engineers working on the FreeBSD port and while
> upgrading to TOT, I noticed that there appears to only be 1 sort queue
> for all guest domain devices (xlbd_blk_queue).  All disks end up
> pointing at this request queue.  The strategy call (do_blkif_request)
> uses this global queue and attempts to dequeue using elevator sort.
> Does any kind of sort make sense given that multiple devices feed this
> queue?
>
> I ask because some of the new recovery code attempts to call
> kick_pending_request_queues() in blkif_connect().  In my FreeBSD version
> prior to this I was using per disk sort queues, which was fine since I
> would only try to kick the i/o on interrupt completion.  In this newer
> context it seems like having only 1 queue avoids the need to keep a
> table of per-disk sort queues.
>
> Thanks for any help.
>
>     Eric
>
>
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