Re: Intel P6 vs P7 system call performance

From: Ingo Molnar (mingo@elte.hu)
Date: Tue Dec 24 2002 - 15:31:11 EST


On Tue, 24 Dec 2002, Linus Torvalds wrote:

> I realized that there is really no reason to use __KERNEL_DS for this,
> and that as far as the kernel is concerned, the only thing that matters
> is that it's a flat 32-bit segment. So we might as well make the kernel
> always load ES/DS with __USER_DS instead, which has the advantage that
> we can avoid one set of segment loads for the "sysenter/sysexit" case.

this basically hardcodes flat segment layout on x86. If anything (Wine?)
modifies the default segments, it can wrap syscalls by saving/restoring
the modified %ds and %es selectors explicitly.

        Ingo

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