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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