Patrick Chase (patrickjchase.delete@this.gmail.com) on February 4, 2013 11:47 am wrote:
> Michael S (already5chosen.delete@this.yahoo.com) on February 4, 2013 2:27 am wrote:
> > Patrick Chase (patrickjchase.delete@this.gmail.com) on February 3, 2013 2:27 pm wrote:
> > >
> > > With that said, you gave me plenty of evidence yourself. R10K was >50% bigger for a 10% advantage
> > > in integer and a 50% advantage in FP.
> >
> > 50% in FP is for Spec95, I assume.
> > In Spec2k the difference was ALOT bigger - 2.4x.
> > I wonder why Spec2k and spec95 produce so different pictures?
>
> Two words: Cache footprint.
>
> SpecFP95 had a notoriously small working set. SpecFP2k was better in that respect. The R14K you cite had
> an 8 MB external last level cache, vs. 512 KB for the PIII. That big cache gave R14K quite a significant
> benefit in SpecFP2k and similar technical workloads, which is precisely why SGI put it there :-).

There is also an issue of external DRAM bandwidth. The PIII-500's chipsets used a single 64-bit SDR SDRAM channel if I recall correctly. Peak STREAM bandwidth was on the order of a couple hundred MiB/sec.

The Origin used 128-bit DDR per node (it's a NUMA), so it would have had ~4X the bandwidth to memory on even a single node. Peak STREAM bandwidth was close to 1 GiB/sec.

As I said in my previous post, a LOT changes in the 2 years between when that PIII-500 came out and when the R14K did.

I can't believe I remember this stuff. Time to go get my brain erased...