Date: Fri, 14 Jan 2005 10:43:00 -0500 From: John Baldwin <jhb@FreeBSD.org> To: freebsd-alpha@FreeBSD.org Subject: Re: processor type. Message-ID: <200501141043.00568.jhb@FreeBSD.org> In-Reply-To: <20050114074336.GA97061@freebie.xs4all.nl> References: <16866.32790.398095.651691@canoe.dclg.ca> <20050114002651.GD29445@dragon.nuxi.com> <20050114074336.GA97061@freebie.xs4all.nl>
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On Friday 14 January 2005 02:43 am, Wilko Bulte wrote:
> 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-Al
> >pha-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?
Yes. Note that setting CPUTYPE in make.conf gets all the right flags set for
you automagically.
--
John Baldwin <jhb@FreeBSD.org> <>< http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve" = http://www.FreeBSD.org
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