The Intel Xeon 5670: Six Improved Cores

Exotic improvements

With many VMs running on top of a hypervisor, flushing the TLB each time you switched to another VM or to the hypervisor was a costly operation. So the TLBs of the AMD Barcelona cores got a new VM specific tag, called the Address Space IDentifier (ASID). An ASID field was added to each TLB tag.  Intel followed this example more than a year later with its Nehalem CPU. The ASIDs allow the TLB to keep track of which TLB entry belongs to which VM. The result is that a VM switch does not flush the TLB. There's more info on this here.

Since context switching does not only happen between CPUs but also between processes (each process has its own virtual address space), this feature might also be handy for a “native” OS. Some CPU families already incorporated ASIDs a long time ago. Guess. Of course, the famous Alpha CPUs EV4 got this back in 1993. Operating systems will have to support this first, and we don’t expect major performance boosts. Completely exotic is the support for 1 GB pages. 2 MB instead of 4 KB pages make a lot of sense to avoid overwhelming the TLB. But 1 GB pages seem a bit exaggerated until we count our internal RAM in TBs. I was told that a few very exotic HPC applications would be sped up with this. 

And then are of course the obligatory new instructions. Six new instructions have been added to accelerate encryption/decryption using AES. The question remains if the performance improvements are worth the extra debugging time. In some rare cases they might be, but we would be lying if we would say we are enthusiastic about yet another SSE instruction.

The SKUs

Below you find an overview of Intel’s newest line-up. We did not include the AMD’s alternatives as the newest AMD Opteron “Magny-cours” will be launched in a few weeks. The current best AMD Opteron, the six-core Opteron 2435 at 2.6 GHz costs $989. It is clear that this pricing will have to be adjusted downwards with the appearance of both Magny Cours and the new six-core Xeon 5600. We expect the Opteron 2435 to compete with one of the quadcore Xeon E5620 to E5640 models.

Pricing stays the same as the Xeon X5500 series. Intel adjusted its Xeon lineup to better address some niche markets. For the HPC folks with poor thread scaling but with high performance demands there is the rather expensive X5677 quadcore at 3.46 GHz. The cost sensitive market is addressed by the E5620, E5630 and E5640 quadcores. Those parts get a speedbump for the same price.

One of the most interesting offerings is the L5630. Chances are high that you are not quickly CPU power limited once you buy a server based on Westmere cores. One CPU can still cope with 8 threads, realistically address up to 72 GB of RAM per CPU (144 GB maximum) and needs only 10W per core.