PA8800 Dual-Core processors question.

[YLTan]

I want to check if the PA8800 Dual-Core processors is really two cpu or just 2Cpu acting as one logical cpu.

I heard that these two cpu(PA8800 Dual-Core processors) integrated in one wafer are actually acting as one logical cpu providing speed and reliability and cross-checking each other. Not sure if this is true.

If i were to upgrade my current superdome cpu which have 2cpu(with 2cpu sockets) configure in one virtual partition to PA8800 Dual-Core processors, will I be able to have that same partition using only 3cpu(PA8800) assuming only changing the processor chipsets and no other change in cellboard. and use the remaining 1cpu for another virtual partition.

[Mark Grant]

My understanding is that each core has it's own cache although they both share a higher level cache and behave logically two separate entities.

[Ravi_8]

Hi,

as per the talk we had with HP pre sales person, it's 2 cpu acting as single logical unit.

I have no idea about superdome, better clarify with HP.

[YLTan]

I heard the same from our HP CSS support and but not from HP pre-sales. But our HP CSS support can't confirm it.

[Oleg Khoroshylov]

Hi,
I heard that that PA8800 will have the same virtual partitions (vPar) support as PA8700 on HP-UA 11i v1 starting from 2nd quater of 2004. This means that maximum number of virtual partitions will equal the number of CPUs/cores (two for PA8800). As to hardware upgrade, I am not sure that you can use the your old cellboards - you probably will need to replace them.

BR,
OK

[Ted Buis · Accepted solution]

The pa-8800 is true dual core (independent) processors, each with separate 1.5MB L1 cache all on the same die. The processor module incorporates a 32MB L2 cache that is shared. While I believe the plan is to support individual CPUs with vPars, just as if they were separate chips, the performance may be impacted due to the shared L2 cache. This will be have to be tested, before best practices can be established. Since other systems lacked the L2 cache, it may not be much of a factor, but you may want to wait for test results to be published. Moving from the prior pa-risc processors to a pa-8800 requires new cell boards in all partitions and new pa-8800 processors throughout. While they could be mixed in the past, since the pa-8800 uses the Itanium 2 bus, this isn't possible. The good news is that processor to cell controller and memory bandwidth jump significantly in using the sx1000 based cell boards.

[rick jones]

Indeed, HP describes the PA-8800 as two CPUs on a chip. We do not describe it as Sun tries to describe the UltraSPARC-IV as a "dual-threaded CMT CPU" If anything, the shared external cache on the PA-8800 makes it more of a dual-threaded CPU than the shares no caches US-IV.