Common wisdom??

By: Paul A. Clayton (, March 10, 2016 9:33 am
Room: Moderated Discussions
Ricardo B (ricardo.b.delete@this.xxxxx.xx) on March 9, 2016 4:05 pm wrote:
> Paul A. Clayton ( on March 9, 2016 2:22 pm wrote:
> > If you mean "low performance core", I am even more skeptical that "nobody" wants such. A core with
> > 90% the performance of current high-end cores would be much smaller and measurably more energy efficient,
> > especially if there is significant specialization for "server"
> > workloads. While going below half performance
> > may not be useful (given the area and power overheads of the memory system),
> >
> 1) I don't think that 90% of a Skylake core performance is what anyone would call "low performance".

I was not insisting on the 90% mark for "low performance" but pointing out that (under the invalid assumption of design and process [including binning effects] parity) even a moderate reduction in targeted performance can introduce significant benefits in power/area. I would probably consider a 75% target to be "low performance", especially if referring to "server workload" performance (low ILP workloads benefit less from common performance optimizations).

> 2) That you can hit 90% of Intel's fat performance with "much smaller
> and measurably more energy efficient" core is an unproven assertion.

I was under the impression that such was common wisdom, that getting that 11% more performance at the high end required disproportionate costs in area and power (under parity in design effort and process). Perhaps such is mistaken. (I seem to recall that (in the late 1990s?) out-of-order execution was claimed to provide about a 35% performance boost. Obviously, power-area does not increase in proportion to performance.)

(Note that I used weasel wording of "much smaller" and "measurably more".)

However, the fact that Intel does not provide processors with even higher performance implies that the power-area (and design effort) cost of increasing performance does not increase linearly with performance at least at that level of performance.

> Eg, Apple's A9 core seems to be almost as big as a Skylake core.

Intel's Atom offerings provide another counter in that the performance/power/area tradeoffs seem discouraging. Some of that presumably came from lower design effort (though the lack of integrated memory controller on the initial Atoms seems to me like a bad choice).
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TopicPosted ByDate
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    X-Gene 3 power enelopecanon2016/03/09 09:32 AM
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      Nobody wnats low performance server processors?Ricardo B2016/03/09 05:05 PM
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            bad size comparison between Apple A9 and skylake coresHeikki Kultala2016/03/12 05:37 AM
              bad size comparison between Apple A9 and skylake coresAlberto2016/03/12 02:04 PM
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        Common wisdom??Paul A. Clayton2016/03/10 09:33 AM
          Common wisdom??Ricardo B2016/03/10 10:49 AM
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          X-Gene 3 power enelopeRonald Maas2016/03/22 07:49 AM
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