Re: Intel P6 vs P7 system call performance

From: Ulrich Drepper (
Date: Fri Dec 20 2002 - 05:08:48 EST

Linus Torvalds wrote:

> For _zero_ gain. The jump to the library address has to be indirect
> anyway, and glibc has several places to put the information without any
> mmap's or anything like that.

Correct. The current implementation is optimal.

It is necessary to have indirection since the target address can change.

I'm never going to use self-modifying code.

And it's a simple, one-instruction change.

  int $0x80 -> call *%gs:0x18

That's it. It's all implemented and tested. The results are in the
latest NPTL source drop. The code won't be available in LinuxThreads
since it requires a kernel with TLS support.

As far as I'm concerned the discussion is over. I'm happy with what I
have now. The additional overhead for the case when AT_SYSINFO is not
available is neglegable (and can be compiled-out completely if one
really wants), and in case AT_SYSINFO is available the code really is
the fatest possible given the constraints mentioned above.

--------------.                        ,-.            444 Castro Street
Ulrich Drepper \    ,-----------------'   \ Mountain View, CA 94041 USA
Red Hat         `--' drepper at `---------------------------

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