Re: [PATCH] Mutilated form of Andi Kleen's AMD prefetch errata patch

Dave Jones
2003-09-30T13:53:51Z

On Tue, Sep 30, 2003 at 02:39:36PM +0100, Jamie Lokier wrote:
> Dave Jones wrote:
> > This looks to be completely gratuitous. Why disable it when we have the
> > ability to work around it ?
>
> Because some people expressed a wish to have kernels that don't
> contain the workaround code, be they P4-optimised or 486-optimised
> kernels.

And those people are wrong. If they want to save bloat, instead of
'fixing' things by removing <1 page of .text, how about working on
some of the real problems like shrinking some of the growth of various
data structures that actually *matter*.

The "I don't want Athlon code in my kernel because I run a P4 and
it makes it slow/bigger" argument is totally bogus. It's akin to
the gentoo-esque "I compiled my distro with -march=p4 and now
my /bin/ls is faster than yours" argument.

> After all we have kernels that don't contain the F00F
> workaround too. I'm not pushing this patch as is, it's for
> considering the pros and cons.

F00F workaround was enabled on every kernel that is possible
to boot on affected hardware last time I looked.
This is what you seem to be missing, it's not optional.
If its possible to boot that kernel on affected hardware,
it needs errata workarounds.

> CONFIG_X86_PREFETCH_WORKAROUND makes more makes more sense with the
> recently available "split every x86 CPU into individually selectable
> options" patch, and, on reflection, that's probably where it belongs.

Said patch isn't included in mainline, so this argument is bogus.
Relative merits of that patch were already discussed in another thread.

Dave

--
Dave Jones http://www.codemonkey.org.uk