Re: [PATCH] x86/asm/entry/64: pack interrupt dispatch table tighter

[H. Peter Anvin]

On 04/03/2015 11:37 AM, Linus Torvalds wrote:
> On Fri, Apr 3, 2015 at 11:35 AM, H. Peter Anvin <hpa@xxxxxxxxx> wrote:
>>
>> For the record, I actually measured the impact of the jump-to-jump when
>> I wrote it.  It has a small, *but measurable*, positive impact.
> 
> What did you compare against, and how did you measure that? I don't
> see how it could *possibly* be faster than just a simple aligned "push
> + jmp".
> 

I wish I remembered the exact details; it took a fair bit of gathering
numbers as the spread was quite a bit wider than the delta, but in the
end there were two distribution peaks clearly offset.

I seem to remember it involving a loop running RDTSC continuously and
another RDTSC in the interrupt path.

	-hpa


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