Path: utzoo!mnetor!tmsoft!torsqnt!news-server.csri.toronto.edu!rpi!usc!sdd.hp.com!hp-pcd!hpfcso!stroyan
From: stroyan@hpfcso.FC.HP.COM (Mike Stroyan)
Newsgroups: comp.sys.hp
Subject: Re: shared memory on fixed address on 9000/825
Message-ID: <7370349@hpfcso.FC.HP.COM>
Date: 27 Mar 91 18:00:03 GMT
References: <1991Mar26.190339.13805@rusmv1.rus.uni-stuttgart.de>
Organization: Hewlett-Packard, Fort Collins, CO, USA
Lines: 17

>On several *ixes i can supply the shmat-call with a address, at which i
>want to access the shared memory. This works apparently also on a 9000/375
>with HP-UX 7.0.
>The man page on the 825 claims however, that this is not possible on this
>machine...
>
>So, PLEASE, why ?  And is there a workaround for this ?

The 800 series caches data by its virtual address rather than it's
physical address.  This means that all processes must agree on the
virtual addresses of shared memory segments so that the memory locations
will end up in the same cache entries for all processes.  These forced
addresses are the same from one process to the next.  They are also
allocated on a system basis, so that you will never have address
collisions when attempting to map segments.

Mike Stroyan, mike_stroyan@fc.hp.com