Fantastic latency on Live CD, horrible on HDD

Hey all,

Here are my computer's specs

AMD Althon XP 3000+
512 mb of DDR333 (2x256 modules)
Asus a7v8x motherboard
nVidia Geforce 4 ti 4600
Quantum Fireball harddrive from an iMac

I can run 10.04 and 8.04 from the live cd with sub 15k latency jitter consistently.

When installed to my harddrive, the numbers are lower, but spike when I open a program that has not been launched since startup (not in cache?). It spikes to about 8ms. This problem doesn't exist when running from the LiveCDs.

Anyone have any thoughts? I have 8.04 installed on my HDD at this point in time.

Hi John,

thanks for the reply. Zero swap is being utilized, although I did make the swap partition 1.2gb just for laughs.

I think you made a typo when you said 512 Kb. I was under the impression that 512 mb was more than enough for linuxcnc under 10.04 or 8.04

Edit: only 30% of memory is being used with linuxcnc 2.5 running under 8.04 off my HDD

Thanks,
Luke

Not a problem at all John, any help or ideas are welcome.

I'm not sure what tklinux is, and when I try to run it from bash prompt it says 'command not found' so I'm not sure where to go with this one.

Although I would stress that the spike ONLY happens on first launch after a fresh start up.

Example: post fresh start up, I launch firefox. BOOM! 8ms jitter for a split second, then back to normal. Close firefox, and open it again, no increase in jitter.

It's only when a program is first started

Hi

I learnt today that SWAG means "Scientific Wild Assed Guess"!
I am obviously not very internet acronym and text speak savvy!

Is this a ATA / IDE machine?
I take it you have the HDD jumpered master on IDE0 and the CDROM jumpered as slave on IDE0 or master on IDE1 with both on the correct ribbon connector?

My starting SWAG, that they are on different buses, does swapping this change things?

It might be worth swapping ports in either case and testing.

(If SATA, likewise try other ports, but sounds like it is probably an IDE vintage MB)

regards

I've been totally unable to run latency testing while LinuxCNC is open, so while I can run tklinux I can't see my latency numbers to see what that does.

All the best,
Luke

It is an IDE motherboard, you are correct. Currently I have

HDD jumpered to master on the last port on the cable hooked up to the primary IDE channel
CDROM jumpered to master on the last port on the cable hooked up to the secondary IDE channel

Come to think of it, I previously had this machine with HDD master, CDROM slave on primary channel and I dont recall there being this jump in latency. I will try this right now and get back to you.

Thanks,
Luke

ArcEye,

It appears that you have done it!

All situations that would cause the latency to jump are now gone.

The solution (for the time being) was to make the HDD the only IDE peripheral attached to the computer set to master on primary channel.

I cannot break 8k/9k no matter what I try.

I'll do a longer stress test now as I finish up my CNC router.

Perfect timing!

I'll post back the final results.

Thank you everyone for your help including those who helped me out in the IRC channel.