Re: Intel P6 vs P7 system call performance

[H. Peter Anvin]

Linus Torvalds wrote:
> 
> Uli's suggested glibc approach is to just put the magis system call 
> address (which glibc gets from the AT_SYSINFO elf aux table entry) into 
> the per-thread TLS area, which is alway spointed to by %gs anyway.
>
> THIS WORKS WITH ALL DSO'S WITHOUT ANY GAMES, ANY MMAP'S, ANY RELINKING, OR
> ANY EXTRA WORK AT ALL!
> 
> The system call entry becomes a simple
> 
> 	call *%gs:constant-offset
> 
> Not mmap. No magic system calls. No relinking. Not _nothing_. One 
> instruction, that's it. 
> 

Unfortunately it means taking an indirect call cost for every invocation...

	-hpa