Travis (travis.downs.delete@this.gmail.com) on October 30, 2016 6:34 pm wrote:
> juanrga (noemail.delete@this.juanrga.com) on October 29, 2016 9:47 pm wrote:
> > anon (spam.delete.delete@this.this.spam.com) on October 28, 2016 4:13 am wrote:
> > > juanrga (noemail.delete@this.juanrga.com) on October 28, 2016 2:02 am wrote:
> >
> >

My point is that Apple can target 4GHz for some future chip, miss some few IPC percents
> > compared to current designs and then recover those percents via hardware improvements.

> >
>
> Your claim doesn't make a lot of sense. The point is that frequency and IPC exist two somewhat
> opposite points in the multi-dimensional tradeoff space used in CPU design - more "brainy"
> designs may give up frequency to get more IPC.

You are repeating what I said before. I wrote there is inverse relation between IPC and frequency, and I wrote that this inverse relation is the basis for the traditional definition of speed-demons and brainiac desings.

> The main point made was that you can't simply evaluate in a quantitative way the coefficients in this
> tradeoff (i.e., how much IPC you gain by reducing f) by taking an existing chip and downclocking it!
> That will only give a small IPC boost due to decreased relative DRAM latency (and perhaps L3 or L4
> latency for systems where those caches are in a separate clock domain). The main IPC benefit to reduced
> frequencies is missed: the ability to use the longer clock cycles to stuff in more logic per pipeline
> stage, to reduce the number of pipeline stages, to increase cache sizes, whatever.

That wasn't the point.

We are not saying that taking a given F chip and underclocking it to F/2 gives a measure of the IPC that would have a chip initially designed for F/2.

This is the second time that my point is ignored.

> Claiming that the same logic works in reverse is nonsensical - you can't just upclock a 2 Ghz design
> to 4 Ghz, unless the design was terrible and left a lot on the table in the first place...

I didn't write that same logic applies. I said that essentially the same law applies to the IPC/F relation, but with different parameters, of course.

I think here the confusion here relies on that I am considering a single law with different parameters, whereas some of you are taking the different expressions with different parameters as different laws.