Date: Fri, 14 Jan 2005 19:26:55 +0100 From: Wilko Bulte <wb@freebie.xs4all.nl> To: John Baldwin <jhb@FreeBSD.org> Cc: freebsd-alpha@FreeBSD.org Subject: Re: processor type. Message-ID: <20050114182655.GC630@freebie.xs4all.nl> In-Reply-To: <200501141043.00568.jhb@FreeBSD.org> References: <16866.32790.398095.651691@canoe.dclg.ca> <20050114002651.GD29445@dragon.nuxi.com> <20050114074336.GA97061@freebie.xs4all.nl> <200501141043.00568.jhb@FreeBSD.org>
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On Fri, Jan 14, 2005 at 10:43:00AM -0500, John Baldwin wrote..
> 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.
I think I need to go and just investigate, but let me fire another silly
question:
Where does this kind of option get set for a make release? I need to
avoid any /etc/make.conf stuff making its way into the Alpha releases
I build ;-)
I sort of expect the settings in /etc/make.conf to only apply to building
world and not to building release. Correct?
--
Wilko Bulte wilko@FreeBSD.org
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