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SubjectRe: Intel P6 vs P7 system call performance

On Tue, 17 Dec 2002, Dave Jones wrote:
> I'm sure I recall seeing errata on at least 1 CPU re sysenter.
> If we do decide to go this route, we'll need to blacklist ones
> with any really icky problems.

The errata is something like "all P6's report SEP, but it doesn't
actually _work_ on anything before the third stepping".

However, that should _not_ be handled by magic sysenter-specific code.
That's what the per-vendor cpu feature fixups are there for, so that these
kinds of bugs get fixed in _one_ place (initialization) and not in all the
users of the feature flags.

In fact, we already have that code in the proper place, namely

/* SEP CPUID bug: Pentium Pro reports SEP but doesn't have it */
if ( c->x86 == 6 && c->x86_model < 3 && c->x86_mask < 3 )
clear_bit(X86_FEATURE_SEP, c->x86_capability);

so the stuff I sent out should work on everything.

(Modulo the missing syscall page I already mentioned and potential bugs
in the code itself, of course ;)


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