canavan wrote:Isn't the RM7000's on-die 2nd level cache much faster than the external cache of the R5k / R5k2? I'd still assume that the swap is not worth the risk and cost.
Well, it is marginally faster. The interesting point is that O2 RM7000 modules have what would be the R5000 or RM5271 L2 cache still there as the RM7000 L3 cache. So you're going from 2x32KB L1 + 1MB L2 to 2x16KB L1 + 256KB L2 + 1MB L3, and this allows an RM7000 module to run circles around an RM5200.
Given that a 350MHz RM7000 O2 is roughly 30% faster than a 300MHz RM5271, a 266MHz RM7000 would be roughly the same performance as the RM5271, maybe a bit worse.
Overall, it will depend on the kind of workload you are doing with this system. CPU-bound tasks will run slower (because of the speed decrease), memory-bound tasks will run faster (because of larger cache), and I/O-bound tasks will run at the same speed (because the PCI bus speed will not change).
R3000 (alas, dead) R4000
x4 R4400 R4400
x2 R8000 R10000 R4000PC R4000SC R4400SC R4600 R5000SC R5000
x3 RM7000 2xR10000 R12000 2xR12000
- 2x2xR10000 R16000 4xR16000
among more than 150 machines : Apollo, Data General, Digital, HP, IBM, MIPS before SGI
, Motorola, NeXT, SGI, Solbourne, Sun...