How Many Processor Cores Are Enough?
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From: ranjit_mathews@yahoo.com on 10 Oct 2006 01:03 Bill Todd wrote: > ranjit_mathews(a)yahoo.com wrote: > > Bill Todd wrote: > >> ranjit_mathews(a)yahoo.com wrote: > >>> Greg Lindahl wrote: > >>>> In article <1160421201.367674.89490(a)c28g2000cwb.googlegroups.com>, > >>>> ranjit_mathews(a)yahoo.com <ranjit_mathews(a)yahoo.com> wrote: > >>>> > >>>>>> Spec/GHz is very nearly totally meaningless. > >>>>> Then why does the Core 2 Duo find favor over Pressler core processors? > >>>> Because Core2 is faster at lower power? Note that "GHz" doesn't appear > >>>> in the sentence; Ghz is just an implementation detail, not comparable > >>>> between designs. > >>> No, since for a given design, if you know ops/GHz, you can estimate > >>> what the ops would be at (say) 50% more GHz. > >> And what, exactly, do you believe you have gained once you've done that? > > > > If you can estimate how much faster they can clock it relative to how > > much faster other processors can be clocked, you can estimate how much > > faster it will get relative to other processors. > > That, as the saying goes, is a mighty big 'if'. > > On what basis would you estimate how much faster those processors can > clock, anyway? I don't know the field. How do competing processor designers do it? Do they never have the faintest idea how much stiffer the competition can get? > It's certainly not simply a matter of GHz, since in a > given process different processor designs have wildly different maximum > clock rates (depending, of course, on the complexity of the slowest of > their pipeline stages, among other things).
From: Bill Todd on 10 Oct 2006 01:23 ranjit_mathews(a)yahoo.com wrote: > Bill Todd wrote: >> ranjit_mathews(a)yahoo.com wrote: >>> Bill Todd wrote: >>>> ranjit_mathews(a)yahoo.com wrote: >>>>> Greg Lindahl wrote: >>>>>> In article <1160421201.367674.89490(a)c28g2000cwb.googlegroups.com>, >>>>>> ranjit_mathews(a)yahoo.com <ranjit_mathews(a)yahoo.com> wrote: >>>>>> >>>>>>>> Spec/GHz is very nearly totally meaningless. >>>>>>> Then why does the Core 2 Duo find favor over Pressler core processors? >>>>>> Because Core2 is faster at lower power? Note that "GHz" doesn't appear >>>>>> in the sentence; Ghz is just an implementation detail, not comparable >>>>>> between designs. >>>>> No, since for a given design, if you know ops/GHz, you can estimate >>>>> what the ops would be at (say) 50% more GHz. >>>> And what, exactly, do you believe you have gained once you've done that? >>> If you can estimate how much faster they can clock it relative to how >>> much faster other processors can be clocked, you can estimate how much >>> faster it will get relative to other processors. >> That, as the saying goes, is a mighty big 'if'. >> >> On what basis would you estimate how much faster those processors can >> clock, anyway? > > I don't know the field. I think that was beginning to become obvious. Don't you think it's a bit presumptuous to contradict someone under those circumstances? - bill
From: ranjit_mathews@yahoo.com on 10 Oct 2006 01:34 Bill Todd wrote: > ranjit_mathews(a)yahoo.com wrote: > > Bill Todd wrote: > >> ranjit_mathews(a)yahoo.com wrote: > >>> Bill Todd wrote: > >>>> ranjit_mathews(a)yahoo.com wrote: > >>>>> Greg Lindahl wrote: > >>>>>> In article <1160421201.367674.89490(a)c28g2000cwb.googlegroups.com>, > >>>>>> ranjit_mathews(a)yahoo.com <ranjit_mathews(a)yahoo.com> wrote: > >>>>>> > >>>>>>>> Spec/GHz is very nearly totally meaningless. > >>>>>>> Then why does the Core 2 Duo find favor over Pressler core processors? > >>>>>> Because Core2 is faster at lower power? Note that "GHz" doesn't appear > >>>>>> in the sentence; Ghz is just an implementation detail, not comparable > >>>>>> between designs. > >>>>> No, since for a given design, if you know ops/GHz, you can estimate > >>>>> what the ops would be at (say) 50% more GHz. > >>>> And what, exactly, do you believe you have gained once you've done that? > >>> If you can estimate how much faster they can clock it relative to how > >>> much faster other processors can be clocked, you can estimate how much > >>> faster it will get relative to other processors. > >> That, as the saying goes, is a mighty big 'if'. > >> > >> On what basis would you estimate how much faster those processors can > >> clock, anyway? > > > > I don't know the field. > > I think that was beginning to become obvious. Don't you think it's a > bit presumptuous to contradict someone under those circumstances? It's also obvious that competing processor designers do it somehow; it seems most unlikely that they wouldn't try to estimate the headroom left in a competing processor.
From: Nick Maclaren on 10 Oct 2006 04:29 In article <1160443523.429549.264960(a)h48g2000cwc.googlegroups.com>, "ranjit_mathews(a)yahoo.com" <ranjit_mathews(a)yahoo.com> writes: |> |> > > No, since for a given design, if you know ops/GHz, you can estimate |> > > what the ops would be at (say) 50% more GHz. |> > |> > And what, exactly, do you believe you have gained once you've done that? |> |> If you can estimate how much faster they can clock it relative to how |> much faster other processors can be clocked, you can estimate how much |> faster it will get relative to other processors. Several of the regular posters (including me) are old enough to remember when that was the case, but I suspect that you aren't :-) On most CPUs, it isn't as simple as 50% more GHz is 50% more operations per cycle, even in artificial codes that don't access memory or do I/O. Even if it were, such codes are SO artificial that their performance is almost irrelevant to actual work. Regards, Nick Maclaren.
From: ranjit_mathews@yahoo.com on 10 Oct 2006 06:51
Nick Maclaren wrote: > In article <1160443523.429549.264960(a)h48g2000cwc.googlegroups.com>, > "ranjit_mathews(a)yahoo.com" <ranjit_mathews(a)yahoo.com> writes: > |> > |> > > No, since for a given design, if you know ops/GHz, you can estimate > |> > > what the ops would be at (say) 50% more GHz. > |> > > |> > And what, exactly, do you believe you have gained once you've done that? > |> > |> If you can estimate how much faster they can clock it relative to how > |> much faster other processors can be clocked, you can estimate how much > |> faster it will get relative to other processors. > > Several of the regular posters (including me) are old enough to remember > when that was the case, but I suspect that you aren't :-) > > On most CPUs, it isn't as simple as 50% more GHz is 50% more operations > per cycle, even in artificial codes that don't access memory or do I/O. If your competitor ships a computer with a 1.6GHz processor and DDR2-533 RAM and you figure that they can get their processor to run at 3.2Gz by the time DDR3-1066 RAM becomes mainstream, you know they'll be able to compress or run a DOM parser about twice as fast, don't you? > Even if it were, such codes are SO artificial that their performance is > almost irrelevant to actual work. Aren't the above actual work? > > > Regards, > Nick Maclaren. |