Messages in this thread | | | Date | Thu, 11 Sep 2003 20:18:06 +0200 | From | Andi Kleen <> | Subject | Re: [PATCH] 2.6 workaround for Athlon/Opteron prefetch errata |
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On Thu, 11 Sep 2003 18:48:39 +0100 Jamie Lokier <jamie@shareable.org> wrote:
> Andi Kleen wrote: > > signal exception path is thousands of cycles, we're talking about tens > > of cycles here. > > <hand-waving> > > Tens vs thousands == percentage points.
It is more thousands than tens :-)
[just the page fault alone is quite costly]
> > Isn't it about 20 cycles per mispredicted branch on a P4? > > Five of those and we're talking several percent slowdown, ridiculous > as it seems.
There are a lot of conditional branches in the signal path. If you don't believe me I can send you simics full instruction traces of it. I'm not going to believe that 2-3 more make a significant difference.
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