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Re: Benchmark performance

To: <wgowcher@yahoo.com>, "Atsushi Nemoto" <nemoto@toshiba-tops.co.jp>
Subject: Re: Benchmark performance
From: "Kevin D. Kissell" <kevink@mips.com>
Date: Thu, 16 Aug 2001 11:11:56 +0200
Cc: <linux-mips@oss.sgi.com>
References: <20010809215522.A1958@lucon.org><20010813173446.61234.qmail@web11901.mail.yahoo.com> <20010816125652N.nemoto@toshiba-tops.co.jp>
Sender: owner-linux-mips@oss.sgi.com
> Current CVS kernel uses FPU emulator unconditionally.  If one floating
> point intruction causes a 'Unimplemented' exception (denormalized
> result, etc.) following floating point instructions are also handle by
> FPU emulator (not only the instruction which raise the exception).
> 
> I do not know this is really desired behavior, but here is a patch to
> change this.  If Unimplemented exception had been occured during the
> benchmark, aplying this patch may result better performance.

Not desired behavior, just an artifact.  However, I agree with Carsten
that changing the API to the emulator for this and using a counter
as you have done is not appropriate, and that the existing CPU
configuration flag is a more appriate mechanism.  It's possible
that Wayne's baseline numbers came from a pre-Algor-emulator
kernel, and that this "feature" accounts for some of his degraded
performance.  But I'd be surprised if it accounted for all of it,
unless his FP test does 10% of its calculations on denormalized
numbers or something.

            Kevin K.


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