Custom GRUB on Live USB?

More
22 Dec 2021 04:48 #229695 by rohal
Hi,

I want to see if the cheap computer I have just bought (Dell Optiplex 780) is a suitable candidate for LinuxCNC.

Researching the forum brings up two possibilities to improve latency; disable hyperthreading in the bios and isolating one core in the cpu (isolcpus = 1).

The second option requires the boot loader GRUB to be modified (isolcpus = 1 added).  I am not sure how to do this, but have installed 'grub-customizer' and could probably work-out how to proceed (any hints welcome).

My question is: can grub be altered on the Live version?  Seems a reasonable idea as it is just a text file on the USB, but I haven't been able to find a definitive answer.  At worst, the USB iso could just be re-created if corruption occurred.  Any ideas appreciated.

Thanks

Roger

Please Log in or Create an account to join the conversation.

More
22 Dec 2021 05:52 #229700 by ALittleOffTheRails
You'd basically have to "respin" the ISO, to modify the grub config permanently.

Unfortunately I don't know of an easy way to do this.

I think if you press TAB (I've used that many different live versions of various Linux this may not be actually correct, but there should be some kind of hint relating to that ) that gives you the option of altering the kernel cmdline for that boot. so you would just have to add
isolcpus=1
then continue on with the boot process.

Please Log in or Create an account to join the conversation.

More
22 Dec 2021 07:24 #229703 by rohal
Replied by rohal on topic Custom GRUB on Live USB?
Thanks for the reply.

TAB does bring up a command line, but entering isolcpus=1 doesn't change the latency; which is 24600ns with 6 windows of glxgears.

I have also turned off audio, pcie ports and hyperthreading (called Intel Speed Step on this Dell).

So, not great latency, but maybe ok for my simple machine...

Please Log in or Create an account to join the conversation.

More
22 Dec 2021 08:04 - 22 Dec 2021 08:06 #229704 by ALittleOffTheRails
Should be ok for using a Parallel Port, just don't expect any OTT feed rates.

Turn off any and all power saving.

you can also try,
isolcpus=1 processor.max_cstate=1 intel_idle.max_cstate=0


Is it a Dual or Quad core CPU ?
Last edit: 22 Dec 2021 08:06 by ALittleOffTheRails.

Please Log in or Create an account to join the conversation.

More
22 Dec 2021 10:04 #229710 by rohal
Replied by rohal on topic Custom GRUB on Live USB?
It is a dual core Intel E7500 with 4GB ram and parallel port on the motherboard.

Thanks for the further hints.

Please Log in or Create an account to join the conversation.

Time to create page: 0.139 seconds
Powered by Kunena Forum