[LAU] another cpu question

[Gene Heskett]

On Sunday 14 September 2014 06:55:06 Joakim Hernberg did opine
And Gene did reply:
> On Sat, 13 Sep 2014 19:44:19 +0200
> 
> Ede Wolf <listac at nebelschwaden.de> wrote:
> > The price advantage for the AMD would probably be eaten up by the
> > more expensive colling - I prefer it rather quiet - and the higher
> > energy bill. But if it would be the more adequate CPU for this very
> > workload, I would go that route.  i7 are all HT, so that would leave
> > the i5 as only other option.
> 
> IME, HT dosen't have to be a showstopper.  It's conceptually "wrong" to
> use it if you are relying on linux realtime processing, but in real
> life it's normally not a problem with audio, unless you push the
> system real hard doing other things.  I also theorize that on an i7 it
> can lead to cache depletion and cause long xruns when the CPU is
> heavily loaded.
> 
> On the other hand you can normally just disable HT in the BIOS, so with
> the right motherboard it shouldn't be a criteria to disqualify a CPU.

At risk of depleting the supply of atom powered boards, the dual core 
atom, fanless, with HP disabled and isolcpus=1 on the kernel command line 
in grub, is easily the best latency board for use with LinuxCNC, where the 
background i/o task runs on the isolated core, and can update the parport 
every 25 usecs, with a timing jitter under 3 microseconds.  But its 
relatively poorly equipt in dram.  Only 2 slots, but runs LCNC very nicely 
with a 2Gb slab of ddr3 in it, and has enough left over to run a session 
of firefox and a session of the irc agent konversation while its cutting 
metal by controlling dangerously powerful machinery.

The stuff running on core 0 may lag, but LCNC keeps chugging along on the 
isolated core 1.

You folks really should take advantage of the isolcpus command for your 
latency critical work.  The gui's may not keep up, but the sound should.

Cheers, Gene Heskett
-- 
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page <http://geneslinuxbox.net:6309/gene>
US V Castleman, SCOTUS, Mar 2014 is grounds for Impeaching SCOTUS