CPU & RAM upgrade beyond dual core + 2GB worth it?

Im wondering whether its worth upgrading my CPU and RAM from a 2.66Ghz Core 2 Duo + 2GB DDR2 800 to a Core 2 Quad +4GB DDR2 800?

The pages I've found seem to be out of date as they talk about RTAI misbehaving with over 1GB of RAM installed.

Page: wiki.linuxcnc.org/cgi-bin/wiki.pl?Hardware_Requirements

Cost of the upgrade is trivial, especially the RAM, just wondering if anybody has any up to date info on whether the newer builds of LinuxCNC can make use of the extra?

The machine is using an SSD so there probably isnt much need for a RAMdisc.

I've already got the ISOLCPU thing done, so is 2 cores enough or can it make use of another couple for IRQs or Classic Ladder or something?

Thanks for any advice you can give, JHC

Hi

Very little point.

The kernel switch isolcpus= X, isolates the numbered cpus so that it is just running on CPU 0 normally.
So no point adding more cpus, just to take them out of use.

See my FAQS for some more info on latency and why isolcpus works
www.linuxcnc.org/index.php/english/forum...-the-latency-problem
www.linuxcnc.org/index.php/english/forum...me-latency-solutions

Linuxcnc does not consume huge amounts of memory, unless you have a huge CAM produced gcode file, which will use memory both for the trajectory planner and the plot preview (if using Axis)
4GB is an option, just be aware that the maximum the system will be able to see in 32 bits, is 3.25GB approx, so some of it will be wasted and anything above 4GB will achieve nothing

The pages I've found seem to be out of date as they talk about RTAI misbehaving with over 1GB of RAM installed.

Page: wiki.linuxcnc.org/cgi-bin/wiki.pl?Hardware_Requirements

To allow for both EMC and its host Ubuntu Linux installation to coexist comfortably, you should have at least 256MB of RAM, though 512MB is preferable. [The remainder of this paragraph is current as of late-May 2008] All RTAI versions prior to the not-yet-released vulcano CVS version misbehave in physical memory configurations larger than 1GB. Consequently, the kernel on the Ubuntu 6.06-based Live-CD available through www.linuxcnc.org was configured intentionally to recognize only the first 1GB of RAM (of which 896MB is available). This large-memory problem should go away Real Soon Now when a new version of RTAI is released and integrated into the EMC distribution. The kernel on the Ubuntu 8.04-based Live-CD has been configured to recognize more than 1GB of RAM in anticipation of this new version of RTAI which then wasn't released in time, so proceed with caution.

That wiki is hugely out of date, as can be seen immediately by the Ubuntu version 6 it is talking about

I have a 64bit rtai kernel with a 64bit build of MachineTalk ( a linuxcnc fork ) running on an 8 core i7 with 16GB of RAM, so there is no large memory problem.
(This is a house development machine and the spec would make no sense whatsoever for a machine controller)

With a SSD your machine sounds plenty fast enough, so long as the basic latency is good, which has no relationship to processing power

regards

Ah, I had a feeling that was the case but its good to have it confirmed.

I've ~0 linux background so was a little unsure of what the isolcpus thing did, my (mistaken) impression was that it would shunt all the non-realtime stuff onto another core and reserve one purely for the realtime stuff - I didnt realise it just disabled it.

With a SSD your machine sounds plenty fast enough, so long as the basic latency is good, which has no relationship to processing power

Yes, latency is remarkably good. Its a Commell FS-97DXG2 PICMG board, 2x GB ethernet, Core 2 Duo E6750 2.66GHz 4M 1333Mhz FSB, 2Gb DDR2 800, 60Gb SATA III SSD.
I did some reading and disabled all the power management stuff, SpeedStep, FDD, audio, RS232/485, LPT, etc then added the isolcpus line.
Im using a Mesa 5i20 so latency is less of an issue in any case.

The board has LVDS output, so Im going to attempt to run an old laptop LCD alongside a normal VGA connected one.
Its possible in an electrical/mechanical sense, but I anticipate opening a can of worms rather than whoop-ass when I actually try it...

My backplane has 14 ISA slots along with 4x PCI, and I've got a few old 8255 PIO cards so I thought Id give them a try.
I know theres no proper driver and I cant write C, but for using for stuff like blinkenlights, fan control, and any other time insensitive stuff I thought I might just use a script or batch file to tickle its registers.
Being good old '70s tech theres no disagreeable PCI type nonsense that requires strict timing.
I know theres probably enough spare GPIO between the 5i20 and the LPT, but its nice to have access to an ISA bus again and all this stuff needs using - this is the project where I finally get to use all the 'it'll come in useful one day' bits & bobs.
If I get it working I'll do a writeup, same for the LVDS LCD stuff.

Thanks for the info.

JHC