Mark (nospamplease.delete@this.nothereorthere.com) on May 20, 2022 12:15 pm wrote:
> Linus Torvalds (torvalds.delete@this.linux-foundation.org) on May 20, 2022 11:32 am wrote:
> > Brendan (btrotter.delete@this.gmail.com) on May 20, 2022 4:06 am wrote:
> > >
> > > To me, supporting dissimilar CPUs (for both "different ISA" and "same ISA with different instruction
> > > timings") is an interesting engineering challenge [...]
> >
> > That's an odd way to spell "stupid and pointless".
> >
> > We already know what the problem is. Intel already did the "expose that cores
> > are different" thing in their desktop/laptop chips. It was an abject and fundamental
> > failure that is basically unfixable, and Intel already disabled it.
> >
> > So no, it's not an "engineering challenge". It was a broken product. It's the
> > same kind of "engineering challenge" that Itanium was. Just give it up.
> >
> > Linus
>
> Impossible or merely painful?
>
> Catch the unimplemented instruction.
> Tag the process as fat core only.
> Reschedule and restart the instruction

You end up with everything running on big cores this way. Because the "unimplemented" instruction will be utilized in some core library. Because why wouldn't it be, if it makes the code run faster.