Re: CSCAN I/O scheduler for 2.6.10 kernel

[Jens Axboe <axboe@suse.de>]

On Tue, Apr 04 2006, Bill Davidsen wrote:
> Vishal Patil wrote:
> >Maintain two queues which will be sorted in ascending order using Red
> >Black Trees. When a disk request arrives and if the block number it
> >refers to is greater than the block number of the current request
> >being served add (merge) it to the first sorted queue or else add
> >(merge) it to the second sorted queue. Keep on servicing the requests
> >from the first request queue until it is empty after which switch over
> >to the second queue and now reverse the roles of the two queues.
> >Simple and Sweet. Many thanks for the awesome block I/O layer in the
> >2.6 kernel.
> >
> Why both queues sorting in ascending order? I would think that one 
> should be in descending order, which would reduce the seek distance 
> between the last i/o on one queue and the first on the next.

Then it wouldn't be CSCAN, now would it? :-)

-- 
Jens Axboe