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

[Jamie Lokier]

Andi Kleen wrote:
> > 	if ((addr & 3) == 0)
> > 		return 0;
> 
> Maybe. But gcc generates quite good code (binary decision tree) code for
> the switch() statement already so I don't think it is worth it to go 
> through complications just to avoid that.
> 
> The decoder looks big in C, but when you take a look at its hot path in 
> assembly it is quite fast.

I wonder.  No part of the signal path looks especially slow, and yet
as a whole it isn't that fast.  The odd percentage slowdown here and
there is quite bothersome.

GCC generates a decision tree.  You realise that about half of the
branches in that tree will be mispredicted?

-- Jamie
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