Date: Mon, 1 Mar 2010 13:24:54 -0800 (PST) From: James Phillips <anti_spam256@yahoo.ca> To: freebsd-questions@freebsd.org Subject: Re: Compiler Flags problem with core2 CPU Message-ID: <997836.8570.qm@web65512.mail.ac4.yahoo.com> In-Reply-To: <20100301100655.B3D801065676@hub.freebsd.org>
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> Date: Sun, 28 Feb 2010 22:37:27 +0800
> From: Aaron Lewis <aaron.lewis1989@gmail.com>
> Subject: Re: Compiler Flags problem with core2 CPU
> To: Paul B Mahol <onemda@gmail.com>
> Cc: freebsd-questions@freebsd.org
> Message-ID: <4B8A7FA7.1070200@gmail.com>
> Content-Type: text/plain; charset=ISO-8859-1;
> format=flowed
>
> Really ? It's bad to use custom flags to compile kernel ,
> why do you
> think so ?
> I'd like to know more about this : )
>
> So setting optimize compiler flags is only useful for
> userland stuff ?
>
I laughed at your question because I remember reading somewhere that using aggressive optimization options is a good way to find compiler bugs. I think that extends of optimizations for "new" CPU architectures as well.
I also heard kernel code avoids MMX instructions for some reason: it may have to do with interrupt handling (fewer registers=faster?). x86 (and AMD64) processors are backwards compatible, so you don't strictly need the latest instructions.
Regards,
James Phillips
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