HSW arch article

Anand wrote a very good article on HSW architecture. I enjoyed it as usual, like his articles on SNB, NHM, Merom before. It is very good to know that some things I thought to be confidential are actually public, like OOO window size (number of u-ops in flight).

I also enjoyed a discussion, especially this bit:

Reader:
>Given the long timescales of CPU design, there would be overlap between the Haifa team working on Sandy Bridge/Ivy Bridge
>(particularly Ivy Bridge) and the Hillsboro team working on Haswell. I was wondering if you knew how much opportunity there is
>for learning between consecutive designs in terms of magnitude of changes possible and timescales before things are pretty
>much fixed? I'm in no position to judge, but I was also wondering based on your knowledge of the architectures and/or
>interactions with members of the design teams if you sense any distinct difference in design philosophies between the Haifa and
>Hillsboro teams. Afterall, the Haifa team's background was in power-efficient, mobile-oriented designs whereas Hillsboro was
>high-performance, desktop/server oriented. You mentioned in the article that Haswell goes back to Nehalem's 3 clock domains
>due to lessons learned from Sandy Bridge/Ivy Bridge. While I don't doubt that's the primary reason, I wonder if design philosophy
>played a role too since Nehalem and Haswell are both Hillsboro designs and maybe they like 3 clock domains.

Anand:
>I wondered the same thing about the correlation between design teams and decisions in Nehalem/Haswell, I refrained from
>speculating on it in the article because I didn't necessarily see any reason to doing so, but I definitely noticed the same
>correlation. It could just be a coincidence though. Nothing else beyond the L3 cache frequency really stood out to me as being
>an obvious common thread between Nehalem and Haswell though.

Someone from the Hillsboro Design Team:
>Anand, thanks for the insights. We all enjoyed it very much and look forward to getting the real thing into your labs.

>As for the design team philosophy, the Hillsboro design team continually tries to outdo the Haifa design team and vice versa.
>Both teams have access to the other teams' design collateral, as we co-own the tick-tock model.

>Next, the reasons for the "3" clock domains are too complicated (and confidential) to go into. Since designing for "2" clock
>domains is much simpler, the reason is not that we enjoy pain and misery. Suffice to say, that you are missing a very big piece
>of the puzzle and accurate conclusions as to why this was done cannot be drawn from the information you have. And the number
>of clock domains is in quotes because those are not accurate anyhow.