Re: Putrid Elevator Behavior 2.4.18/19

[Jeff V. Merkey]

On Wed, Mar 27, 2002 at 08:03:25AM +0100, Jens Axboe wrote:
> On Tue, Mar 26 2002, Jeff V. Merkey wrote:
> > > 
> > > That's good news.
> > > 
> > > Are you still working on the A/B list patch?  I'd imagine that it could make
> > > several problems easier to fix in the block layer.
> > > 
> > 
> > Yes.  I am asking Darren Major, who wrote the A/B implementation 
> > in NetWare to review the patch before we submit it.  It may affect
> > some drivers.  We are verifying that the change I instrumented 
> > will not break anything.
> 
> I'm curious how you are doing this cleanly in 2.4. There are lots of
> places in the kernel that do direct list management on the queue_head.
> Are you adding two separate hidden lists and splicing content to the
> queue_head?

Correct.  I am still reviewing drivers and kernel code to ascertain 
whether I am not leaving any holes.  I have spliced it as a non-obtrusive 
implementation that preserves the existing code with no changes.  

Some of the drivers may have problems if they cache the head address
of the current list.

> 
> 2.5 has this done much more cleanly (of course I'm very biased). See the
> deadline I/O scheduler patch I've posted before, stuff like this can be
> done a lot cleaner there. Internal I/O scheduler structures are
> completely hidden from drivers.
> 

2.5 would be nice, but 2.4.X needs it too and this is the kernel we are 
using for our development and testing, so we will need it there.  

Jeff