[LAD] 4-6 or 8 cores ??

Jonathan Woithe jwoithe at just42.net
Mon Jun 24 01:48:21 UTC 2013

Hi Geoff

On Sun, 16 Jun 2013 20:49:26 +1000 you wrote:
> Going to finally build a new machine. I'ts going to be Intel this time - 
> AMD for 15 years or so - can any one here give some advice as to how 
> many cores are optimal given current kernel >3.8 performance. Any 
> install/operational issues? Any pitfalls ?

I can't provide much in the way of scientific evidence; there are others who
know far more about the technical realities of this - and push their
machines much harder - than I do.

Personally, I have always run with the idea that so long as one has N
independent processes whose links to other processes are limited to the
consumption or production of streams, then one could theoretically max out N
CPU cores.  However in most practical cases involving audio and video one is
running the streams at real world speed, and this obviously limits the
extent that each process requires a CPU.  The only time a single process
would have the chance to max out a single CPU core would be when
freewheeling with jack for example, or doing a final render of a video. 
If one spends most of the time interacting with their AV software, this
means that there's no simple answer to the "how many cores are optimal"
questions.  It depends on the precise mix of software you're running, what
each process requires of a CPU core, how much I/O each process instigates,
and so on.  Another caveat is jackd: my current understanding is that jack2
can better utilise multiple cores, but I'm happy to be corrected on this
point by anyone with more knowledge than I (I really haven't looked into
this recently because for my current situation it's academic).

My system has been based on a first-generation i7 for the last couple of
years and I've noticed no major issues.  However, in terms of audio work I'm
not really pushing the system all that hard during real work (I don't have
soft-synths running generally, and the plugins I use tend to be fairly
frugal with CPU requirements).  This gives me 4 cores with hypertheading
and when I've done tests to see what it could handle, an audio-like workload
is able to push well above the 400% loading (so the hyperthreading seems to
be doing something useful).

Having said all that and knowing the sort of work you do, I would probably
err on the side of getting as many cores as you can reasonably afford.  As
time goes on they won't go astray; you'll have the flexibility to experiment
with new ways of doing things without being too constrained by the number of
cores at your disposal.

A final comment is that with the release of Intel's Haswell-based CPUs we
are at an interesting point in time.  These new cores are certainly a big
win for mobile computing due to their lower power consumption for a given
performance level.  However, whether the increase in outright performance -
the primary metric for a desktop - justifies the "new product" premium these
will attract for the next 6-12 months remains to be seen, especially since
one would also expect some runout discounting on the 4th generation CPUs in
the coming months.


More information about the Linux-audio-dev mailing list