Before I throw this computer in the garbage....

So I've been trying to make the switch from Mach3 to LinuxCNC (due to having some issues with my spindle stopping for no apparent reason and losing steps, which may or may not have anything to do with Mach3) and as it turns out, my computer is absolutely terrible when it comes to latency. I've spent the better part of 2 days reading the various troubleshooting guides and have done most of what there is to do (turning off everything it the BIOS, isolcpus=1,2,3 in GRUB2, putting in a PCI based graphics card) and still the latency is off the chart, though I have gone from 800us+ jitter to 400us+ jitter from these efforts. It's not even in the ballpark, leading me to believe this is a hopeless case or something obvious is out of kilter.

Before I just move on and put together a new controller computer based on hardware that is known to work, I'm wondering if anyone else has gotten such atrocious performance and are there any low hanging fruit I might have overlooked?

Hardware: Dell Optiplex 755, I5 4 core 2.4Ghz, 2GB ram, 500GB HDD (80GB for linux, dual boot with windows vista) Asus HD 5450 Silent graphics card (added to see in onboard graphics was causing the problem.)

Screenshots attached.

Thanks!

Are you sure that's an I5? and a Dell 755?

AFAIK a Dell Optiplex 755 is a Core Duo (socket 775) machine

They also come with the Core 2 Quad option, apparently. I bought this second hand several years ago. But here's the info:

Edit: BIOS confirms it's a Intel Core2 Quad CPU Q6600 @ 2.40GHz, so I guess it's not an I5.

sun@debian:/proc$ lscpu
Architecture: i686
CPU op-mode(s): 32-bit, 64-bit
Byte Order: Little Endian
CPU(s): 4
On-line CPU(s) list: 0-3
Thread(s) per core: 1
Core(s) per socket: 4
Socket(s): 1
Vendor ID: GenuineIntel
CPU family: 6
Model: 15
Stepping: 11
CPU MHz: 2393.999
BogoMIPS: 4787.99
Virtualization: VT-x
L1d cache: 32K
L1i cache: 32K
L2 cache: 4096K
sun@debian:/proc$ dmesg
[ 0.000000] Initializing cgroup subsys cpuset
[ 0.000000] Initializing cgroup subsys cpu
[ 0.000000] Linux version 3.4-9-rtai-686-pae (Debian 3.4.55-4linuxcnc) () (gcc version 4.6.3 (Debian 4.6.3-14) ) #1 SMP PREEMPT Debian 3.4.55-4linuxcnc
[ 0.000000] BIOS-provided physical RAM map:
[ 0.000000] BIOS-e820: 0000000000000000 - 000000000009ec00 (usable)
[ 0.000000] BIOS-e820: 00000000000f0000 - 0000000000100000 (reserved)
[ 0.000000] BIOS-e820: 0000000000100000 - 000000007ddff800 (usable)
[ 0.000000] BIOS-e820: 000000007ddff800 - 000000007de53c00 (ACPI NVS)
[ 0.000000] BIOS-e820: 000000007de53c00 - 000000007de55c00 (ACPI data)
[ 0.000000] BIOS-e820: 000000007de55c00 - 000000007e000000 (reserved)
[ 0.000000] BIOS-e820: 00000000e0000000 - 00000000fed00400 (reserved)
[ 0.000000] BIOS-e820: 00000000fed20000 - 00000000feda0000 (reserved)
[ 0.000000] BIOS-e820: 00000000fee00000 - 00000000fef00000 (reserved)
[ 0.000000] BIOS-e820: 00000000ffb00000 - 0000000100000000 (reserved)
[ 0.000000] Notice: NX (Execute Disable) protection missing in CPU!
[ 0.000000] SMBIOS 2.5 present.
[ 0.000000] DMI: Dell Inc. OptiPlex 755 /0PU052, BIOS A04 11/05/2007
...rest omitted.

it may be of little to no value, but here is the output from lscpu for my optiplex 360 with a c2d processor and integrated graphics, Max Jitter is around 15000:

linuxCNC:~$ lscpu
Architecture: i686
CPU op-mode(s): 32-bit, 64-bit
Byte Order: Little Endian
CPU(s): 2
On-line CPU(s) list: 0,1
Thread(s) per core: 1
Core(s) per socket: 2
Socket(s): 1
Vendor ID: GenuineIntel
CPU family: 6
Model: 23
Stepping: 6
CPU MHz: 2526.822
BogoMIPS: 5053.64
L1d cache: 32K
L1i cache: 32K
L2 cache: 3072K

Unless a few mhz makes that much difference vs a couple cores. It sounds like you've done your due diligence to fix the problem, I'd say there's something wrong with the hardware and it might not be worth saving the computer at this point. Have you tried booting from the live cd and running the latency test?

I have not tried the SMI mod, mostly because as you note the latency is constant rather than periodic, and the mod seems to involve compiling kernals and such, which is a bit more complex an undertaking than I cared to take given the symptoms. Something major is interrupting the hell out of the CPU and I can't figure out what. I suspect I can even see it scrolling down web pages in a browser, in the form of horizontal graphical glitches in the video as I scroll (or at least I'm guessing it's related.)

At this point I'm back to mach3 until I can assemble a linuxcnc friendly controller and take the time to configure it (my spindle is step based )

But thanks for the suggestions!

OK Thanks! I'll try that. I guess my eyes glazed over when I hit the part about compiling the kernal (presumably for an earlier version) and I stopped there.

One of the pictures you posted show 4 cores? but I'm pretty sure that is a 2 core CPU, are you sure you remember to disable hyper-threading in the Bios?

OK Thanks! I'll try that. I guess my eyes glazed over when I hit the part about compiling the kernal (presumably for an earlier version) and I stopped there.

The smi fix is not something you can just try.

Read this and if your chipset matches you can apply it

www.linuxcnc.org/index.php/english/forum...me-latency-solutions