Re: elevator priorities vs. full request queues

[Jens Axboe <axboe@suse.de>]

On Tue, Jul 13 2004, Werner Almesberger wrote:
> Jens Axboe wrote:
> > It's just that if default io prio was something other than 0, then it
> > would make sense to set it there.
> 
> Oh, I see. Yes, of course. It actually does this, implicitly,
> since the default value of zero just happens to be what bio_init
> sets already ;-)

Only if you define 0 to be the default value :-)

> > But I suppose you just want io submission to set it, in which case it
> > doesn't matter what bio_init() sets it to.
> 
> Except for those bios that get submitted without ever touching
> submit_bh.

You mean things like bio_map_user/bio_copy_user and (at the other end,
doubt these would count), bios submitted privately to the drive itself
(ala ide-scsi)? The latter can be disregarded imho, nothing to worry
about. The former allocate requests on its own, so you must pass in the
priority there. So instead of assigning bio priority and using that for
request allocation, you are just a step or two further down in the call
chain and specify the priority there directly.

In short, I don't see a problem there.

-- 
Jens Axboe