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SubjectRe: Intel P6 vs P7 system call performance
Ulrich Drepper wrote:
> Nakajima, Jun wrote:
>
>>AMD (at least Athlon, as far as I know) supports sysenter/sysexit. We tested it on an Athlon box as well, and it worked fine. And sysenter/sysexit was better than int/iret too (about 40% faster) there.
>
>
> That's good to know but not what I meant.
>
> I referred to syscall/sysret opcodes. They are broken in their own way
> (destroying ecx on kernel entry) but at least they preserve eip.
>

syscall is pretty much unusable unless the NMI is changed to a task
gate. syscall does not change %esp on entry to the kernel, so an NMI
before the manual stack switch would still use the user stack, which is
not guaranteed to be valid - oops. x86-64 gets around this by using an
interrupt stack, its replacement for task gates.

--
Brian Gerst

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