Re: io_request_lock patch?

Mike Anderson
2001-07-11T21:06:21Z

Jens Axboe [axboe@suse.de] wrote:
> On Thu, Jul 12 2001, Dipankar Sarma wrote:
> > On Wed, Jul 11, 2001 at 09:20:22PM +0200, Jens Axboe wrote:
> > > True. In theory it would be possible to do request slot stealing from
> > > idle queues, in fact it's doable without adding any additional overhead
> > > to struct request. I did discuss this with [someone, forgot who] last
> > > year, when the per-queue slots where introduced.
> > >
> > > I'm not sure I want to do this though. If you have lots of disks, then
> > > yes there will be some wastage if they are idle. IMO that's ok. What's
> > > not ok and what I do want to fix is that slower devices get just as many
> > > slots as a 15K disk for instance. For, say, floppy or CDROM devices we
> > > really don't need to waste that much RAM. This will change for 2.5, not
> > > before.
> >
> > Unless there is some serious evidence substantiating the need for
> > stealing request slots from other devices to avoid starvation, it
> > makes sense to avoid it and go for a simpler scheme. I suspect that device
> > type based slot allocation should just suffice.
>
> My point exactly. And typically, if you have lots of queues you have
> lots of RAM. A standard 128meg desktop machine does not waste a whole
> lot.

I would vote for the simpler approach of slots. :-).

>
> --
> Jens Axboe

--
Michael Anderson
mike.anderson@us.ibm.com