Date: Fri, 14 Jan 2005 08:43:37 +0100 From: Wilko Bulte <wb@freebie.xs4all.nl> To: freebsd-alpha@freebsd.org Subject: Re: processor type. Message-ID: <20050114074336.GA97061@freebie.xs4all.nl> In-Reply-To: <20050114002651.GD29445@dragon.nuxi.com> References: <16866.32790.398095.651691@canoe.dclg.ca> <20050114002651.GD29445@dragon.nuxi.com>
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On Thu, Jan 13, 2005 at 04:26:51PM -0800, David O'Brien wrote..
> On Mon, Jan 10, 2005 at 08:16:06AM -0500, David Gilbert wrote:
> > I see in the compiler lines crawling by that gcc is asked to optimize
> > for 'EV5' while being compatible with 'EV4'. My Alpha is an EV4 ---
> > I'm wondering if I would see better performance with a different flag
> > there, but the gcc manual doesn't even acknowledge the existance of
> > the options that are in use, let alone the available options.
>
> It doens't???
>
> >From /usr/share/mk/bsd.cpu.mk:
> . elif ${MACHINE_ARCH} == "alpha"
> _CPUCFLAGS = -mcpu=ev4 -mtune=ev5
>
> http://gcc.gnu.org/onlinedocs/gcc-3.4.3/gcc/DEC-Alpha-Options.html#DEC-Alpha-Options
> clearly tells:
>
> -mcpu=cpu_type
> Set the instruction set and instruction scheduling parameters for
> machine type cpu_type. You can specify either the EV style name or
> the corresponding chip number. GCC supports scheduling parameters for
> the EV4, EV5 and EV6 family of processors.
>
> -mtune=cpu_type
> Set only the instruction scheduling parameters for machine type
> cpu_type. The instruction set is not changed.
>
>
> That said, you should remove the -mtune=ev5 or change it to -mtune=ev4.
> My guess is you won't notice a difference, but this this change will
> produce the best code for your machine.
Any idea how drastic -mtune=ev6 would change things on a DS10 (to name
a random box ;-) ?
Am I correct in assuming that -mcpu=ev4 will result in not using the BWX
etc of the newer CPUs? And that -mcpu=ev6 will result in code that does
not run on anything older than EV6 due to missing instructions etc?
W/
--
Wilko Bulte wilko@FreeBSD.org
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