Re: driver concurrency

[Thor Lancelot Simon <tls%panix.com@localhost>]

On Tue, Dec 02, 2014 at 12:52:51PM +0900, Masao Uebayashi wrote:
> On Tue, Dec 2, 2014 at 5:32 AM, Thor Lancelot Simon <tls%panix.com@localhost> wrote:
> > Try it!  It's quite a mess, particularly around target and bus attach/detach.
> 
> scsipi and wscons are the worst in that respect.
> 
> (Who wants to be a hero?)

Dear Mr. Hero,

I have a couple of NetBSD kernel projects every winter, to give me
something to do during my commute (in the winter, I take the train; in
the summer, I bike).

The way I pick them is that I have to be able to restart the project
every week or so, having forgotten where I was, and figure out what I
was doing again in 20 minutes or less -- my commute is about 50 minutes.
That way I can get at least 30 minutes of stuff done any day I don't
have something else to do.

I tried "devise locking scheme for SCSI code" as one of those
projects for about a week last winter.  Utterly hopeless.  Perhaps
someone more clever or dedicated can make some progress, but I would
suggest it is the kind of work that will require several consecutive
days and a lot of planning just to get started -- and hours of effort
at a time, over several weeks to finish.

My best guess using my OOMA Engineering Manager's Manual is that
actually getting any meaningful concurrency in the SCSI code, for disks,
is about 20 or 30 hours of work total.  So if you are lucky enough to
have 3 consecutive hours of spare time every  day, 5 days a week, and you
trust my guesswork, you can assume you are looking at somewhere between 1
and 2 weeks of hacking.

I have a wide array of SCSI controllers and targets that would let you
exercise many of the drivers.  If you're serious about this, send me a
project plan to indicate your interest and I will send them to you or
provide access.

-- 
 Thor Lancelot Simon	                                      tls%panix.com@localhost
"From the tooth paste you use in the morning to the salt on your evening meal,
it's easy to take for granted the many products brought to us with explosives."
    - Institute of Manufacturers of Explosives, "Explosives Make It Possible"