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Date:      Tue, 23 Feb 1999 20:57:30 -0800 (PST)
From:      Matthew Jacob <mjacob@feral.com>
To:        Terry Lambert <tlambert@primenet.com>
Cc:        dfr@nlsystems.com, freebsd-hackers@FreeBSD.org
Subject:   Re: Panic in FFS/4.0 as of yesterday
Message-ID:  <Pine.LNX.4.04.9902232053270.23433-100000@feral-gw>
In-Reply-To: <199902240142.SAA25033@usr09.primenet.com>

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There was some moderately appropos discussion today at OSDI about this -
plus a quite amusing discussion of virtual machines. One of the issues
has to do with resource allocation (and, by relation, resource scheduling)
problems when it's hard to figure out whom is driving or paying for an
I/O.

But I can see there isn't much interest in this in FreeBSD. That's okay-
I'd be just happy to have a system that doesn't crash.

On Wed, 24 Feb 1999, Terry Lambert wrote:

> > The only problem with this approach is not all I/O is or will be driven
> > by a process. Let's say we port a new filesystem in that creates a
> > *lot* of I/O via threads or wads of async r/w. Unless you start doing
> > thread scheduling it's hard to figure out whome to penalize.
> 
> I think this would be an evil thing (kernel threads).  The idea that
> you have an atomic context semi-precludes preemption without a lot
> of redesign work.  On the plus side, it might force a redesign, but
> I doubt the code would make it in if that happened.
> 
> 
> > I still would like to see a B_EXPEDITE (although B_PRIORITY seems a better
> > name). Should we also be paying attention to B_ORDERED and should you
> > consider doing buffer generations?
> 
> I stayed away from B_PRIORITY because that implies a spectrum of
> priority levels, not just an "I may be slow, but I'm in front of you".
> 
> Passing the bits down is somewhat problematic, since they are pretty
> much stripped before they get there.  It's really an interface
> isolation issue that I think would be very hard to deal with.
> 
> 
> 					Terry Lambert
> 					terry@lambert.org
> ---
> Any opinions in this posting are my own and not those of my present
> or previous employers.
> 



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