X-pop3-spooler:	POP3MAIL 2.1.0 b 3 961213 -bs-
Delivered-To:	pcg AT goof DOT com
Date:	Tue, 14 Apr 1998 13:07:57 +0200 (CEST)
From:	Ronald Wahl <rwahl AT gmx DOT net>
X-Sender:	rwa AT goliath DOT csn DOT tu-chemnitz DOT de
To:	beastium-list AT Desk DOT nl
Subject:	Re: [performance] newer binutils / pgcc / K6
In-Reply-To:	<Pine.LNX.3.96.980414020447.12999B-100000@goliath.csn.tu-chemnitz.de>
Message-ID:	<Pine.LNX.3.96.980414125424.14957B-100000@goliath.csn.tu-chemnitz.de>
MIME-Version:	1.0
Sender:	Marc Lehmann <pcg AT goof DOT com>
Status:	RO
Lines:	30

On Tue, 14 Apr 1998, Ronald Wahl wrote:

> Hi,
> 
> I noticed a performance problem starting with release 2.8.1.0.26 of
> binutils. If I run nbench on my K6 with binutils 2.8.1.0.26 (or higher)
> some tests will be slower. My first thoughts were that it had something to
> do with the changes hjl made from 2.8.1.0.25 to 2.8.1.0.26 but after some
> further testing I found out that it is a code alignment issue. If I use
> -malign-loops=2 the tests run nearly at the same speed as with the older
> versions of binutils (gas). Some tests are a bit slower but not much
> (--> see my appended nbench results). Other alignments will cause
> slowdowns. Before changing any defaults for loop alignment on a K6 in pgcc
> - is someone willing to play a bit with old and new releases of binutils
> and some other benchmarks or real world applications?

I tested around by myself and found out that real world applications will
often run slower with -malign-loops=2. My guess is that in nested loops
dummy code (from the alignment) consumes decode slots. This will result in
a loss of performance. So my question: Is it possible to align loops only
if these are not nested in another loop (with a high loop count) or if
the alignment code will never be executed?

ron

-- 
\ Ronald Wahl --- rwahl AT gmx DOT net         \   Gib Gates keine Chance!   /
 \ WWW: http://www.tu-chemnitz.de/~row/  \                           /
  \ Talk: rwa AT goliath DOT csn DOT tu-chemnitz DOT de  \   Pinguine schuetzen.   /
   \ PGP key available                     \                       /

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