Re: [PATCH] 2.6 workaround for Athlon/Opteron prefetch errata

[Andi Kleen]

On Thu, 11 Sep 2003 18:48:39 +0100
Jamie Lokier <jamie@xxxxxxxxxxxxx> 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.

-Andi
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