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From: aegl@root44.UUCP
Newsgroups: comp.arch
Subject: Re: Fastest Kernel Make
Message-ID: <421@root44.co.uk>
Date: Sun, 6-Sep-87 04:44:44 EDT
Article-I.D.: root44.421
Posted: Sun Sep  6 04:44:44 1987
Date-Received: Tue, 8-Sep-87 01:26:59 EDT
References: <26853@sun.uucp> <2877@sequent.UUCP>
Reply-To: aegl@root44.UUCP (Tony Luck)
Organization: Root Computers Ltd, London, England
Lines: 20
Keywords: Making kernel = (or) != speed of machine

We have a sequent balance 21000 with 8 processors which we now use as a
cross devlopment enviroment for UniPlus+ (Trademark of UniSoft Corporation).
During the day when everyone is working on it use of the "-P" flag to make
to use more processors is mildly frowned upon - but in the evening or at
weekends if I'm the only person on I like to speed things up a bit. I used
to just throw in "-P8" to use all 8 processors ... but then I watched the
fancy light display on the front of the cabinet and noticed a fair amount
of flicker in the processor activity lights ... Ah! I thought the C compiler
isn't completely CPU bound (with a 4.2 fast file system and sequents whizzo
disk controller and loads of buffers its close but there's still a little
bit of i/o) - so I tried plotting a graph of real time vs. -Pn - and found
the lowest real time came out at about -P12. So if the people at sequent
trying for the 1 minute kernel compile haven't tried it yet they should try
using '-P' values a little higher than the number of processors they have.

-Tony Luck
--------------
Disclaimer: I don't work for sequent (but if you rush out and buy one today
tell them I sent you - perhaps I'll get lucky and get some commission from
them - I'll split it with you ... honest!)