[Beowulf] Power 6

Vincent Diepeveen diep at xs4all.nl
Sat Aug 25 05:45:37 EDT 2007


----- Original Message ----- 
From: "Li, Bo" <libo at buaa.edu.cn>
To: "Vincent Diepeveen" <diep at xs4all.nl>; "Toon Knapen" <toon.knapen at fft.be>
Cc: <beowulf at beowulf.org>; "Robert G. Brown" <rgb at phy.duke.edu>
Sent: Friday, August 24, 2007 4:57 PM
Subject: Re: [Beowulf] Intel Quad-Core or AMD Opteron


> Intel will have CSI and on die memory controller soon following what AMD 
> has done for a few years.
> HT or CSI will help us build machines based on NUMA or similar 
> architectures.
> Based on current memory technologies, I can't find any methods for "memory 
> wall". And a 4 core processor can eat all memory bandwidth in some cases. 
> With NUMA we can gat machines work as several current machine but 
> connected with fast on-board connection. Image a super computer on 
> desktop, and what's next?
> Many-core processors are coming, how to power beowulf with them? I think 
> it is a very interesting topic.
> Power 6 is a really strange processor for me. It works with a in order 
> architecture. I am looking forward to see any detailed evaluation for it.

I didn't get deep into power6 yet, as odds is near 0% i'll ever run on it, 
but for software that isn't using IBM libraries power6 might get a big 
dissappointment.

My assumption with respect to power6 is that is will keep a very expensive 
cpu, drawing a lot of power.

Now at specint and specfp there is always programs where optimizing X or Y 
suddenly boost that specific program factor 2 or so.

Of course as you see me co-author of sjeng-spec, i happen to know its 
hashtable is 150MB; more wasn't allowed by spec (WEIRD DECISION TAKING OVER 
THERE). That fits nearly in power6's cache of course.

Sjeng-spec, in contradiction to the better software, is needing quite some 
bandwidth internally for move storage (using many integers whereas in Diep 
for example is use 1 or 2 integers). All that should on paper be a major 
advantage for power6. For evaluation sjeng-spec uses a function table, which 
i use in Diep too, and which had let crash several compilers from big 
manufacturers for their 'spec'  test compile, years ago. In itself another 
interesting question why something completely legal in C, which actually 
gets used in quite some software, let those compilers crash.

Point is, normally spoken most cpu's mispredict all this. So that's another 
advantage to power6.

Despite all those huge advantages for a highend chip compared to lowend 
chips,
practical the 4.7Ghz power6 is equal to a 2.x Ghz core2.

Whether it is 2.2Ghz or 2.4Ghz or 2.6Ghz, that''s all not so interesting.
I rechecked 5 times to be sure that i didn't make a mistake interpreting 
specint data.
I didn't even exactly calculate what speed core2 it is equal too. It's just 
so shocking slow for integer work.

Power6 gets delivered in 2008 to the universities. We all know that improved 
intel and AMD cpu's in 2008 will by then for sure clock far over 3Ghz. You 
can of course risk big wars by guessing 3Ghz for AMD and 3.2Ghz for intel, 
it being unclear which of those 2 chips is faster by the time power6 gets 
delivered, but i'm pretty convinced i keep on the safe side saying that for 
the average number crunching program, the small tiny processors are on the 
winning side.

If you go inorder, then deliver within 1 cpu a core or 64+ and clock it 4+ 
Ghz :)

We all remember itanium2 just too well.

You don't buy a power6 just to do matrix calculations. You buy it to run 
software that without much of a modification needs to run generic fast at 
it.

Of course for most universities the choice is a tad more complex. If you 
want 100% garantuee that a new intel Xeon 4 core chip releases start 2008, 
you'll never get it.
If you want garantuees as an university that a new AMD machine by 1 januari 
2008 can deliver you X gflops, that's a bad idea too.

Hardware goes that fast, it's only possible to know at the very last moment 
what amount of gflops an ordered machine is going to deliver.

What can give some garantuees is when AMD+Intel garantuee that a specific 
socket is going to work for a new generations of chips.

That does give the possibility to order a new machine some months in 
advance, without the need for a garantuee with respect to when the faster 
cpu's arrive.

We're speaking about a huge amount ofmoney difference here, not some % of 
total price, but rather some factors of price difference. Seems to me power6 
is still profitting from the way university commissions and subsidy rules 
tend to work.

Power6 might be one of the last highend cpu's.

I am not sure whether we must be sad or happy about just that.

Vincent

> Regards,
> Li, Bo
> ----- Original Message ----- 
> From: "Vincent Diepeveen" <diep at xs4all.nl>
> To: "Toon Knapen" <toon.knapen at fft.be>
> Cc: <beowulf at beowulf.org>; "Robert G. Brown" <rgb at phy.duke.edu>
> Sent: Friday, August 24, 2007 9:37 PM
> Subject: Re: [Beowulf] Intel Quad-Core or AMD Opteron
>
>
>> Even worse,
>>
>> Does SSE2 code of intel not by default in th eintel primitives have an 
>> 'if
>> then else' that at opteron it runs without using SIMD?
>>
>> But apart from that, SIMD at oldie K8 is very slow compared to core2,
>> though not a factor 2. Barcelona for well optimized code should have an
>> IPC in SIMD of up to 40+% faster i guess than core2.
>>
>> So only 2 questions are when they release and especially at *what* price
>> for the 4 socket mainboards.
>>
>> A 16 core barcelona machine with 4 DDR2 memory controllers might be a 
>> very
>> mighty system for all kind of applications that need shared memory to
>> scale well.
>>
>> When releasing Barcelona core within a few months from now, AMD has a 
>> huge
>> lead over intel with respect to 4 core cpu's, as it seems to me.
>>
>> I feel personally intels choice of CPU design using small tiny L1 caches
>> from performance viewpoint is a catastrophic one. If there is just ONE
>> competitor for an intel chip that manages to clock a cpu nearly at the
>> same clock like intel and with the same number of cores, then intel
>> usually gets totally outperformed. Now that intel & AMD produce
>> cpu's at the same type of machines their cpu's, it seems to me
>> that AMD will in general outperform intel.
>>
>> Comparing the 2006 core2 with a 2003 release is not a very fair
>> compare IMHO.
>>
>> We can definitely conclude that intel managed to produce their new
>> generation cpu ( core2) more than 1 year sooner than AMD did do, using a
>> simple trick, namely glueing 2 dual core chips together.
>>
>> In the meantime i keep wondering more and more about intel not having an
>> equivalent on the market for AMD's hypertransport.
>>
>> For highend, when buying multiple socket nodes, it is hard to see intel 
>> as
>> an alternative to barcelona core driven machines, as it doesn't have any
>> form of load balancing thanks to having just 1 memory controller for all
>> cores.
>>
>> Most interesting for scientists might be buying a few nodes with some
>> double rail network and each node consisting out of 4 socket AMD machines
>> quadcore. Initially now perhaps 2Ghz. Then in end 2008 you can
>> upgrade the cpu's to 3+ Ghz.
>>
>> When also putting a lot of RAM onto such AMD machine, then
>> such a node of course also totally annihilates power6, even before power6
>> gets taken into production, against a fraction of the price of a power6
>> node.
>>
>> The advantage of using 4 socket machines for a cluster/supercomputer is
>> obviously the fact that the network costs form a smaller part of the 
>> total
>> solution, meanwhile keeping the total number of nodes limited.
>>
>> A few nodes you could arguably use 8 socket solutions for, not to scale 
>> up
>> to more cores, as most software can't handle such bad memory latencies,
>> but it might be you could even outgun power6 in terms of total memory a
>> node.
>>
>> What is the amount of ram that power6 supports versus the 8 socket AMD
>> solutions?
>>
>> Best Regards,
>> Vincent
>>
>>
>>
>> On Fri, 24 Aug 2007, Toon Knapen wrote:
>>
>>> > I understand that, when comparing Quad-Core Xeons with Opterons,
>>> > people focus on the scability issues of the different multi core
>>> > architectures, but we've run some benchmarks on both and the thing
>>> > that at the time surprised me the most was that if your application
>>> > makes much use of the functions provided by Intel Math Kernel Library,
>>> > a single Xeon core (e.g Clovertown) can be up to twice as fast as a
>>> > single Opteron core.
>>>
>>>
>>> You are comparing Intel MKL on Xeon with what exactly on Opteron? Intel
>>> MKL on Opteron is certainly not optimal. I hope you compared to GotoBLAS
>>> on Opteron.
>>>
>>> t
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>>
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> 

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