Re: Two identical systems, radically different performance

On Tue, Oct 9, 2012 at 9:02 AM, Shaun Thomas <sthomas(at)optionshouse(dot)com>wrote:

> 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

>
> --
> Shaun Thomas
> OptionsHouse | 141 W. Jackson Blvd. | Suite 500 | Chicago IL, 60604
> 312-444-8534
> sthomas(at)optionshouse(dot)com
>
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