Kernel Optimizations for Processors
hemi at puresimplicity.net
Mon Dec 29 15:14:34 PST 2003
On Mon, Dec 29, 2003 at 02:15:15PM -0800, admin at forkthepenguin.com wrote:
> On Mon, 29 Dec 2003, John Baldwin wrote:
> > On 29-Dec-2003 admin at forkthepenguin.com wrote:
> > >> > # NO_F00F_HACK disables the hack that prevents Pentiums (and ONLY
> > >> > # Pentiums) from locking up when a LOCK CMPXCHG8B instruction is
> > >> > # executed. This option is only needed if I586_CPU is also defined,
> > >> > # and should be included for any non-Pentium CPU that defines it.
> > >>
> > >> 'and ONLY Pentiums'
> > >
> > > It also says "should be included for any non-Pentium CPU that defines it"
> > > but how do you know if the C# defines this? Is this another item that
> > > would show up in the "Features" list? I looked at a PI-133 I have and
> > > don't see it :
> > It means that if you have 'cpu I586_CPU' in your kernel config and
> > you aren't running a Pentium, then you can define this option. However,
> > it won't really buy you much since we only install the F00F hack once
> > during bootup and all adding this option will do is just not check for
> > it at bootup.
> Cool, thanks for the clarification. I do not have I586_CPU defined in my
> kernel conf (only I686_CPU) and had no problems building the kernel. Under
> Linux you have to define -march=i586 to build the kernel properly for the
> C3. I bring this up because you can specify CPUTYPE in the
> /etc/defaults/make.conf. According to the notes in that file, the
> following cpus can be defined :
> # Intel x86 architecture:
> # (AMD CPUs) k7 k6-2 k6 k5
> # (Intel CPUs) p4 p3 p2 i686 i586/mmx i586 i486 i386
> # Alpha/AXP architecture: ev6 pca56 ev56 ev5 ev45 ev4
> Does CPUTYPE affect the -march flag? I ask because gnu apparently supports
> the VIA C3 using -march=c3. As a test I set CPUTYPE=c3 and had no problems
> building the kernel nor do I see any evidence that CPUTYPE was pulled from
> make.conf during the kernel build. Is CPUTYPE only used for application
> optimizations? I suspect that adding CPUTYPE=c3 was a misguided assumption
> based on the gnu docs (see below).
Take a look at /usr/share/mk/bsd.cpu.mk to see how CPUTYPE affects compiler
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