Re: Semaphore assembly-code bug
From: Linus Torvalds (torvalds_at_osdl.org)
Date: 10/31/04
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Date: Sat, 30 Oct 2004 18:43:21 -0700 (PDT) To: Andi Kleen <ak@suse.de>
On Sun, 31 Oct 2004, Andi Kleen wrote:
>
> Using the long stack setup code was found to be a significant
> win when enough registers were saved (several percent in real benchmarks)
> on K8 gcc.
For _what_?
Real applications, or SpecInt?
The fact is, SpecInt is not very interesting, because it has almost _zero_
icache footprint, and it has generally big repeat-rates, and to make
matters worse, you are allowed (and everybody does) warm up the caches by
running before you actually do the benchmark run.
_None_ of these are realistic for real life workloads.
> It speed up all function calls considerably because it
> eliminates several stalls for each function entry/exit.
.. it shaves off a few cycles in the cached case, yes.
> The popls will all depend on each other because of their implicied
> reference to esp.
Which is only true on moderately stupid CPU's. Two pop's don't _really_
depend on each other in any real sense, and there are CPU's that will
happily dual-issue them, or at least not stall in between (ie the pop's
will happily keep the memory unit 100% busy).
Linus
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