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Date:      Tue, 22 Jun 1999 12:18:55 -0400 (AST)
From:      Ian Grigg <iang@systemics.com>
To:        freebsd-smp@FreeBSD.ORG
Subject:   Re: Multi processor support?
Message-ID:  <199906221618.MAA15934@systemics.com>

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> > > Heh.  That wouldn't be very symmetric...
> > 
> > No, but having processor affinity would be quite nice.  There's
> > nothing wrong with MP.  
>
> Processor affinity is more than nice.  Work I've done on large HP boxes
> indicate that by putting producer/consumer processes on the same processor
> one avoids a lot of cache coherency issues, and increases bandwidth
> considerably.  Admittedly, this is not true of all applications, but
> having the ability to have two or more processes share a processor can go
> a long way towards tuning application performance.

Are you making the assumption that the two processes
are sharing memory for IPC?  Or, maybe kernel threads?

If not, I don't understand how you improve cache coherency
with separate data sets.

> I would suggest an
> ioctl or other API type interface, with a userland tool to assist ... 

But, I agree with the general context.  Processor affinity
is nice, but should only be an option on top of SMP.  I'd
rather have a good SMP than an MP any day.

iang


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