[Beowulf] General thoughts on Xeon 56xx versus E5 series?

Vincent Diepeveen diep at xs4all.nl
Thu Sep 13 02:11:54 PDT 2012

For normal codes no big difference except for the core count.
the memory scales with the RAM.

i7 56xx has 3 memory channels serving 192 bytes at a time in blocks  
of 64  (abortion possibility after 32 bytes helpful for latency based  
but that's a feature of DDR3 ram rather than a difference between the  
2 cpu's).

e5 has 4 memory channels serving 8 cores. So that's 2 cores @ 4  
threads for each memory channel, just like 56xx.

The cpu for latency based codes is still the same. There should  
however be a difference in throughput of SIMD multiplication code
over the processor generations.

I've heard no one about having a 'higher IPC' nowadays thanks to  
this, yet it's a change that happened throughout the i7 revisions.

Obviously this requires assembler type programming, yet for matrix  
calculations it will be a relevant change as most codes really suffered
from the bad throughput of intel cpu's. AMD was handsdown beating  
intel there some years ago which was the bottleneck for intel in
many prime number type workloads, to give one example.

Of course most of those codes have moved to Nvidia nowadays; the 32  
bits Tesla capbility total owns any CPU for such codes, despite
being 32 bits which simply is quite some instructions overhead  
(simply factor 2+). The GPU's
have no problems getting a good throughput for multiplication, so  
that might be an explanation why this rather important improvement
has gone unnoticed.

You really need to be at low assembler level to notice this, or write  
C code that uses the latest compiler and perfectly vectorizes.

How much of a practical speedup it is, i've heard no one about...

On Sep 13, 2012, at 9:55 AM, Christopher Samuel wrote:

> Hash: SHA1
> On 08/09/12 06:21, Orion Poplawski wrote:
>> Any general thought out there on Xeon 56xx versus E5 performance  
>> wise?
> Not really, but a quick look at the Intel site has some info on the
> basic specs - looking at the released versions only these two have the
> fastest clocks and equal number of cores (6):
> http://ark.intel.com/products/48768/Intel-Xeon-Processor-E5645-12M- 
> Cache-2_40-GHz-5_86-GTs-Intel-QPI
> http://ark.intel.com/products/64616/Intel-Xeon-Processor- 
> E5-2430--15M-Cache-2_20-GHz-7_20-GTs-Intel-QPI
> So the E5 has slightly larger cache, faster QPI, higher TDP,
> can address more RAM and same RRP.. ;-)
> Caveat: in the past I've found howlers on the ARK Intel site,
> so validate any info with external sources!
> cheers,
> Chris
> - --
>  Christopher Samuel        Senior Systems Administrator
>  VLSCI - Victorian Life Sciences Computation Initiative
>  Email: samuel at unimelb.edu.au Phone: +61 (0)3 903 55545
>  http://www.vlsci.org.au/      http://twitter.com/vlsci
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