By: juanrga (nospam.delete@this.juanrga.com), August 8, 2014 12:09 pm
Room: Moderated Discussions
Megol (golem960.delete@this.gmail.com) on August 8, 2014 11:23 am wrote:
> juanrga (nospam.delete@this.juanrga.com) on August 8, 2014 10:49 am wrote:
> >
> > They compared older hardware. Migrating from SB-i7 to HW-i7 introduces little benefits
> > in performance (except when using new AVX2 extensions to x86) but in ARM each gen is
> > not a mere 5-10% faster than former gen but much more. Their choice favored x86.
>
> 5-10% is a huge difference given that it results from slight
> polishing. I have to say this point is nonsense.
My point has been ignored.
> > They used only Intel designs. Using only AMD or a mixture of AMD and Intel
> > would change both performance and efficiency. Their choice favored x86.
>
> But would that be relevant? If Intel processors are the most efficient
> x86 ones available shouldn't that be a wise choice?
If instead comparing Intel designs against ARM Standard cores they had compared AMD designs against best ARM cores, their performance and efficiency values had changed completely.
If they were really comparing ISAs, they would have used a mixture of different chips from different manufacturers to minimize the impact due to concrete archs. and process nodes.
> > They computed the power consumption incorrectly. Their methodology choice favored x86.
> >
> > They used an old compiler that didn't optimize the code for ARM all that would do. Their choice favored x86.
>
> Most code in the wild isn't optimized much.
The software that I use wasn't compiled with their ancient compiler.
> > Also the x86 ISA is full of legacy instructions, which have to be implemented
> > in hardware and then verified/tested which increases development costs and time of development.
>
> Wrong. Legacy instructions need some hardware, true. But most of the functionality
> is implemented in microcode instead of adding complex hardware.
> Now there are some quirks in the x86 ISA that does waste power like handling
> of shift by zero, calculating the auxilary flag (nibble carry) etc. But those
> are far from the most power consuming parts of an OoO processor core.
I gave typical costs and time of implementation of ARM vs x86 before. Resume: 10x more $ and 3x more months for x86.
Some studies estimate that microcode ROM takes about a 20% of die for small cores.
We have independent data showing Intel x86 designs loosing against ARM despite Intel having a clear process node advantage.
The ISA doesn't matter myth has been debunked lots of times.
It is interesting that Intel claims that the ISA doesn't matter, x86 is enough, but then is introducing most of its performance/efficiency gains from new ISA extensions to x86: AVX, AVX2, AVX512, TSX...
> juanrga (nospam.delete@this.juanrga.com) on August 8, 2014 10:49 am wrote:
> >
> > They compared older hardware. Migrating from SB-i7 to HW-i7 introduces little benefits
> > in performance (except when using new AVX2 extensions to x86) but in ARM each gen is
> > not a mere 5-10% faster than former gen but much more. Their choice favored x86.
>
> 5-10% is a huge difference given that it results from slight
> polishing. I have to say this point is nonsense.
My point has been ignored.
> > They used only Intel designs. Using only AMD or a mixture of AMD and Intel
> > would change both performance and efficiency. Their choice favored x86.
>
> But would that be relevant? If Intel processors are the most efficient
> x86 ones available shouldn't that be a wise choice?
If instead comparing Intel designs against ARM Standard cores they had compared AMD designs against best ARM cores, their performance and efficiency values had changed completely.
If they were really comparing ISAs, they would have used a mixture of different chips from different manufacturers to minimize the impact due to concrete archs. and process nodes.
> > They computed the power consumption incorrectly. Their methodology choice favored x86.
> >
> > They used an old compiler that didn't optimize the code for ARM all that would do. Their choice favored x86.
>
> Most code in the wild isn't optimized much.
The software that I use wasn't compiled with their ancient compiler.
> > Also the x86 ISA is full of legacy instructions, which have to be implemented
> > in hardware and then verified/tested which increases development costs and time of development.
>
> Wrong. Legacy instructions need some hardware, true. But most of the functionality
> is implemented in microcode instead of adding complex hardware.
> Now there are some quirks in the x86 ISA that does waste power like handling
> of shift by zero, calculating the auxilary flag (nibble carry) etc. But those
> are far from the most power consuming parts of an OoO processor core.
I gave typical costs and time of implementation of ARM vs x86 before. Resume: 10x more $ and 3x more months for x86.
Some studies estimate that microcode ROM takes about a 20% of die for small cores.
We have independent data showing Intel x86 designs loosing against ARM despite Intel having a clear process node advantage.
The ISA doesn't matter myth has been debunked lots of times.
It is interesting that Intel claims that the ISA doesn't matter, x86 is enough, but then is introducing most of its performance/efficiency gains from new ISA extensions to x86: AVX, AVX2, AVX512, TSX...
