On 10/08/2012 06:40 PM, Craig James wrote:
Nobody has commented on the hyperthreading question yet ... does it
really matter? The old (fast) server has hyperthreading disabled, and
the new (slower) server has hyperthreads enabled.
I doubt it's this. With the newer post-Nehalem processors, hyperthreading is actually much better than it was before. But you also have this:
CPU Speed L3 Cache DDR3 Speed
E5606 2.13Ghz 8MB 800Mhz
E5620 2.4Ghz 12MB 1066Mhz
Even with "equal" threads, the CPUs you have in the new server, as opposed to the old, are much worse. The E5606 doesn't even have hyper-threading, so it's not an issue here. In fact, if you enabled it on the old server, it would likely get *much faster*.
Even more mysterious, because it turns out it's backwards. I copy-and-pasted the CPU information wrong. I wrote:
> old: 2 x 4-core Intel Xeon E5620
> new: 4 x 4-core Intel Xeon E5606
The correct configuration is:
old: 2x4-core Intel Xeon E2606 2.133 GHz
new: 2x4-core Intex Xeon E5620 2.40 GHz
So that makes the poor performance of the new system even more mystifying.
I'm going down there right now to disable hyperthreading and see if that's the answer. So far, that's the only concrete thing that I've been able to discover that's different between the two systems.
We saw a 40% improvement by enabling hyper-threading. Sure, it's not 100%, but it's not negative or zero, either.
Basically we can see, at the very least, that your servers are not "identical." Little things like this can make a massive difference. The old server has a much better CPU. Even crippled without hyperthreading, I could see it beating the new server.
One thing you might want to check in the BIOS of the new server, is to make sure that power saving mode is disabled everywhere you can find it. Some servers come with that set by default, and that puts the CPU to sleep occasionally, and the spin-up necessary to re-engage it is punishing and inconsistent. We saw 20-40% drops in pgbench pretty much at random, when CPU power saving was enabled.
Thanks, I'll double check that too. That's a good suspect.
This doesn't cover why your IO subsystem is slower on the new system, but I suspect it might have something to do with the memory speed. It suggests a slower PCI bus, which could choke your RAID card.
The motherboards are supposed to be identical. But I'll double check that too.
Craig
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Shaun Thomas
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