Messages in this thread | | | Date | Fri, 02 Mar 2007 15:58:41 -0800 | From | "Martin J. Bligh" <> | Subject | Re: The performance and behaviour of the anti-fragmentation related patches |
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> .. and think about a realistic future. > > EVERYBODY will do on-die memory controllers. Yes, Intel doesn't do it > today, but in the one- to two-year timeframe even Intel will. > > What does that mean? It means that in bigger systems, you will no longer > even *have* 8 or 16 banks where turning off a few banks makes sense. > You'll quite often have just a few DIMM's per die, because that's what you > want for latency. Then you'll have CSI or HT or another interconnect. > > And with a few DIMM's per die, you're back where even just 2-way > interleaving basically means that in order to turn off your DIMM, you > probably need to remove HALF the memory for that CPU. > > In other words: TURNING OFF DIMM's IS A BEDTIME STORY FOR DIMWITTED > CHILDREN.
Even with only 4 banks per CPU, and 2-way interleaving, we could still power off half the DIMMs in the system. That's a huge impact on the power budget for a large cluster.
No, it's not ideal, but what was that quote again ... "perfect is the enemy of good"? Something like that ;-)
> There are maybe a couple machines IN EXISTENCE TODAY that can do it. But > nobody actually does it in practice, and nobody even knows if it's going > to be viable (yes, DRAM takes energy, but trying to keep memory free will > likely waste power *too*, and I doubt anybody has any real idea of how > much any of this would actually help in practice).
Batch jobs across clusters have spikes at different times of the day, etc that are fairly predictable in many cases.
M.
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