Re: Intel P6 vs P7 system call performance

From: H. Peter Anvin (hpa@transmeta.com)
Date: Tue Dec 17 2002 - 14:54:01 EST


Richard B. Johnson wrote:
>
> You can call intersegment with a full pointer. I don't know how
> expensive that is. Since USER_CS is a fixed value in Linux, it
> can be hard-coded
>
> .byte 0x9a
> .dword 0xfffff000
> .word USER_CS
>
> No. I didn't try this, I'm just looking at the manual. I don't know
> what the USER_CS is (didn't look in the kernel) The book says the
> pointer is 16:32 which means that it's a dword, followed by a word.
>

It's quite expensive (not as expensive as INT, but not that far from
it), and you also push CS onto the stack.

        -hpa

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