[Beowulf] i7-4770R 128MB L4 cache CPU in compact 0.79 litre box - DIY cluster?

Mark Hahn hahn at mcmaster.ca
Mon Jan 20 14:49:52 PST 2014

> It is a DRAM cache, rather than SRAM.  I haven't researched it any

most people call it eDRAM.

> the 128MB cache is supported by Linux kernel 3.12 (Nov 2013).

I'm not really sure why the kernel would need to do anything...

as for performance, this pretty much says it all:


in other words, if your working set size happens to fit in this cache,
you might find it very interesting.  notice, though, how the observed
memory latency for larger data is made worse by the added layer of caching.
I'm not really sure whether this 8-64M sweetspot is special 
in the marketplace - perhaps you have in mind some particular workload,
especially one which is small-footprint?  perhaps financial MC?

most HPC I see has a memory footprint of 1-2G/core - arguably the 
working set size is smaller.  maybe a quarter that, but still >100 MB.

it seems like vendors are waiting for memory density to increase a bit more
before really jumping on the ram-in-package thing.  it's also not clear 
that everyone is going to follow the path of making it last-level cache.

> Ordinary mass market PC cases, motherboards and i7 CPUs might work out a
> little cheaper, but they would not be as compact, would not have the

why is compactness such an important goal?  for a conventional, air-cool
datacenter, it's pretty comfortable to configure 32-40 cores per U.
I'm not really sure using desktop chips gives much of an advantage
in power-per-ghz*core, but perhaps your argument is more about consumer
rather than server prices?

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