Need some 2022 help with 2005 era PCs getting latency down

Hello all,

I have been playing with LinuxCNC for a few weeks now,  trying to find a PC with decent latency numbers, trying different things in GRUB and such...I am a complete newbie when it comes to Linux, well, 2 weeks of intense learning now, and find myself going around in circles. I have 10 tabs open in Firefox all relating to latency, some of them go back to 2012 and it seems are irrelevant today and some are beyond my understanding.

I am hoping someone can step in here and give me a little guidance, get me back on track to reducing the latency. I have about 8 PCs, mostly 2005-2009, anything from single core P4 to dual core, mostly 2.5-3GHz, a few AMDs, one quad core. I have 4 G RAM to move from machine to machine and have installed both 2.7.15 Wheezy and 2.8.2 Buster onto a 7200 RPM HD so I can test the machine with both OSs. In the GRUB I have isolcpus=1, poll=idle, I have tried the no IRQ balance thing but didn't see any changes, then found that was a thread from 2012. I Blacklisted the pcspkr so that is no longer an issue

I have worked through 3 machines now, tweaking best I can, I have turned off all the BIOS power saving things commonly recommended and run the latency script which runs 5 GLXgears and Jugg a Jug etc in Firefox (man I am sick of that video now, have changed to one I like better) but it only runs on 2.8.2, not Wheezy. I have manged to get the Jitter down to .5 to 2.5 uS on sDev but can't seem to get the Max Jitter below 27-35uS on any of the machines, which tells me I am missing something fundamental. I am not at all familiar with how to play with the Kernal, still learning, but thought I may try to move to 2.8 on Wheezy.

I know I am probably forgetting to tell you a lot of details but I am just heading out to work, I"ll try to add more when I get home, try again with a clear head.

I am really enjoying all this computer work but would feel better if I could see some improvement. I can post some of the HW and LAT files  from the script later as well.

Appreciate any help.

Cheers

PS planning to use parallel port

Early gen quad core AMD systems work great with a Radeon GPU, adding isolcpus=0,1 on the kernel command line. SSD's are a huge help, even at a pinch the flash modules that plug directly into a SATA work, tho compared to an SSD in price they aren't competitive per GB, neither as fast, but better than a mechanical drive.

Working nigh shifts ATM but on Friday I'll have time to pull my AMD machine and find out what actual commandline arguments I used. Tho in the meantime you might get other answers.

Maybe worth a read:
rigtorp.se/low-latency-guide/

Might be a bit over your head ATM:
Be aware that Wheezy uses an 32 bit RTAI type kernel for real time and Buster uses a 64 bit RT_PREEMPT kernel. RTAI used to be the option but RT_PREEMPT is part of the mainline kernel now and generally gets usable results.

Hopefully you can get a decent machine with an on board Parallel Port. Some of the Parallel Port PCI or PCIe cards can be a be hit and miss. This is complicated by the fact that some cheaper boards, because of the PCI ID not being recognised, failing in having a driver loaded. But "We have ways of making zese work", well sometimes .

Thank you for the information and for the link, I started reading it this morning lots to digest I’ll continue when I get home tonight.

Just wondering as I am moving the hard drive from computer to computer testing, whether the command line isolcpu=1 and idle=poll will have any negative effect on single core processors? Or do I need to remove those for testing single core?

Thanks!

Thank you Andy.

As I still have a month or so to go before I finish building the milling machine figuring out all the lead screws motor drives etc., and I would like to learn more about Linux as I have the time right now and all of the computers are out and in the office, I am taking the opportunity to learn as much as I can and find the best PC out of the lot.

Cheers

With all config GUI's Linux isn't too bad for configuring, almost config files are plain text, so it's easy to make backups and restore if you screw up.

Don't do anything has the root user, very easy to mess everything up.
Good way to learn is if you have a decent machine play around with installing and messing around with Linux on a virtual machine.

As long as you show a willingness to learn people with be happy to help.

Thanks for the encouragement, much appreciated.

Well so far I have learned how to modify the GRUB, write some command lines , blacklist the pcspkr, change the latency script to play a movie I prefer to jugg a jug, edited a couple of .conf files...this weekend I plan to update wheezy 2.7.14 to 2.80 to see if that makes a difference. Also my SSD arrived so I will install that as well.

I am having fun, I started building computers back in the late 70's, Sinclair ZX80, TRS-80, then onto hot rodding MB's, I was thrilled when I managed to overclock a PC (by changing the crystal) a 4MHz chip to 6.7MHz, what a screamer! 64K RAM, oooohhhhhh and a 20MB 5 1/4" Rodime hard drive, anyone remember those.  Then in tech school we learned DEC PDP-8 and PDP-11, holy cow, moving up now. Think they used the 8088?? That was 40 years ago....jeez I'm old.

But I digress...back to learning Linux.

Cheers

Well, more learning...I spent 2-3 hours trying to get Clonezilla to duplicate my drive but it couldn't create an sdb part so I gave up and ended up cloning my HDD to SSD with dd, man that is a cool little program, only took about 1/2 hour to clone the 80G drive, works slick as can be.

It is one heck of a lot faster booting and and using Debian and Windoze but the latency on the first computer I tried didn't improve, still 32uS and 3.1uS.

I'll have some more time to play with it this weekend and try some other MBs.

Cheers

I tried a few more PCs today with the new SSD and also updated 2.7.15 Wheezy to 2.8.2 and it made a huge difference in boot loading time and operational speed and found one computer dropped from 32uS to about 17uS, yay!, but I found a weird anomaly which I would like to find out more about.

I have a AMD Athlon quad core 64 bit 3G MB from about 2012, 4G DDR3, it is the fastest computer in my test arsenal and yet it is the worst latency. It plays the HD movies perfectly, GLXgears is smooth, moving around windows is fast and it basically just rips except latency sucks, around 100uS max and 20-25uS sDev. I'm not sure if isolcpus works with AMD so I removed it and then also tried isolcpus=1,2,3. I removed idle=poll as well. The BIOS options are very limited but I tried various options to do with the multicore stuff and it really didn't make any difference.

Anyone run into a computer that just seems to be really fast yet sucks at latency?

More testing with another 3 or 4 boxes tomorrow.

Thanks guys!

Cheers