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

On Wed, March 20, 2013 4:53 pm, Allan Klinbail wrote:
> On Thu, 2013-02-21 at 15:25 +0200, Nedko Arnaudov wrote:
>> Clemens Ladisch <[hidden]> writes:
>>
>> > Chris Caudle wrote:
>> >> 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.
>> >
>> > AMD says (in the optimization manual):
>> > | The AMD Family 15h processor floating point unit (FPU) was designed
>> to
>> > | provide four times the raw FADD and FMUL bandwidth as the original
>> AMD
>> > | Opteron and Athlon 64 processors.  It achieves this by means of two
>> > | 128-bit fused multiply-accumulate (FMAC) units which are supported
>> by
>> > | a 128-bit high-bandwidth load-store system. [...]
>> > | The FPU can receive up to four ops per cycle. These ops can only be
>> > | from one thread, but the thread may change every cycle. Likewise the
>> > | FPU is four wide, capable of issue, execution and completion of four
>> > | ops each cycle. Once received by the FPU, ops from multiple threads
>> > | can be executed.
>> >
>> > So if you're running two FP-heavy threads that happen to interfere
>> with
>> > each other in the most negative way, the theoretical performance will
>> > only be double that of earlier CPUs ...
>> >
>> > In practice, the FPU sharing matters only if you use 256-bit AVX
>> > instructions, because those must be executed in two steps.
>>
>> It is expected that performance of the newer CPU family is better. The
>> point is the possibility of xruns happening occasionally at 50% DSP
>> load.
>
> Has this been tested?
>
> It is interesting, although I'm not upgrading for nearly 2 years... but
> I do recommend systems to people.. currently I have a core i7 desktop
> with hyper-threading turned off for this.. I recommend core i5 ... but
> this machine will become my home server in 2 years so it's okay for
> that..
>
> If AMD can use all 8 cores and not suffer in due to shared fpu (i.e. not
> using 256 bit AVX from how I read this) then the AMD becomes better
> value for money ..
>

Try finding an AMD mobo that doesn't have UEFI... They are making it
harder to run Linux on their solutions these days.




--
Patrick Shirkey
Boost Hardware Ltd

1363764440.22930_0.ltw:2,a <65366.188.26.233.220.1363764431.squirrel at boosthardware dot com>