Re: [Jack-Devel] AMD Bulldozer CPUs, shared FPU and Intel Hyper-threading

On Wed, February 20, 2013 1:06 pm, Patrick Shirkey wrote:
> What's your concern? Jack runs fine on multicore systems I have run it on.
> Why do you think 64 core will be any different to 2 or 4 core?

The issue with bulldozer (and piledriver) is that two integer cores share
a single floating point core, so the scheduler thinks it can schedule two
cores, but depending on whether the processes being scheduled are mostly
integer or mostly floating point, it might work well or there might be
contention for the single FP core.
Bulldozer processors have up to 8 integer cores, not sure where you pulled
the 64 number from.

> Probably because they still cost around $15k - $20k per unit so are mostly
> being used for servers and HPC's.

The most expensive desktop version of Piledriver is the FX-8350 and sells
for US $190.
http://www.microcenter.com/product/401795/FX_8350_4GHz_AM3_Black_Edition_Boxed_Processor

8 integer units, 4 FP units, two memory busses, 4GHz core clock rate.

You can get server variants (Opteron 6200 series) with up to 12 cores at a
lower clock rate for around $400, or up to 16 cores (Opteron 6200 and 6300
series) for around US $800-$1000.

Especially in the desktop variant the processors are priced very
competitively. Unless the scheduler has some kind of visibility into the
use of the FP unit by each process, the scheduler could think that there
was a core available to schedule a RT thread, but the RP core needed by
the thread could actually be busy.  Nedko's concern is probably justified.

-- 
Chris Caudle

1361389042.5106_0.ltw:2,a <aefb322014ff76e6ee4455469777b818.squirrel at email dot powweb dot com>