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Comment by paulfr | Hacker News Reader

> the one other researchers (which I respect much more) discovered in 2006

You seem to be blissfully unaware that they're in fact the same researchers: André Seznec is a co-author of the paper.

This paper is valuable in pointing out that ITTAGE branch prediction performance is a very good predictor of Haswell performance. Because the Haswell algorithm is secret, that should be very helpful to developers who still have to care about branch prediction.

Interpreter developers shouldn't ignore pre-Haswell chips just yet, but if you were to, say, develop a new language your design decisions should be guided by where the puck will be rather than where it used to be.

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> You seem to be blissfully unaware that they're in fact the same researchers: André Seznec is a co-author of the paper.

He's the third signer of the current paper but the first of the 2006 one. It's the case of legitimizing the "research" which only confirms exactly what Intel recently implemented in a given CPU generation, even if the grant is for other goals ("ground-breaking, high-risk projects"). Or, to be clearer, I respect the deeds not the persons.

I fully understand the need for Seznec to be able to claim that the algorithm is really used by Intel and that therefore he co-authored the last paper. But confirming that Intel used ITTAGE is "ground-breaking, high-risk"? No. And does that mean we should never use goto label in the tight loops? No.

The grant is for the DAL project [1], which presumably fits the "ground-breaking, high-risk" label. In such a project, some tasks will be high-risk, some tasks will be low-risk. Quantifying the branch predictor of current processors may be a comparatively easy task, but that doesn't mean it's trivial, useless or outside the scope of the project, which is to improve sequential performance of microarchitectures. Knowing that real-world processors are performing just as well as previous academic research is helpful, because it suggests that there is no difficulty or unrealistic assumption that prevented manufacturers from doing so. Conveying that knowledge to the compiler and interpreter community is important too.

[1] https://team.inria.fr/alf/members/andre-seznec/defying-amdah...

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