It said four cores before I applied all the kernel parameters in the linked document. I think it is the kthread_cpus line that assigns two cores to non-realtime tasks and the isolcpus line that assigns only realtime tasks to the remaining two cores. The parameters did substantially improve latency.
I went ahead and commented out the grub changes and sysctl changes and ran latency histogram again. You can see the four cores and zero isolcpus. -- Ralph ________________________________________ From: Robert Schöftner <r...@unfoo.net> Sent: Tuesday, April 15, 2025 11:59 PM To: Enhanced Machine Controller (EMC) Cc: Ralph Stirling Subject: Re: [Emc-users] Small PC for LinuxCNC CAUTION: This email originated from outside the Walla Walla University email system. Am Dienstag, dem 15.04.2025 um 23:09 +0000 schrieb Ralph Stirling via Emc-users: > Here is the histogram after taking all the steps shown in > https://dantalion.nl/2024/09/29/linuxcnc-latency-jitter-kernel-parameter-tuning.html > and using the stress-ng load generator with one glxgear. > > I lost the pre-tuning screenshot because it saves it in /tmp by > default, which disappears on reboot. Would be nice if the handy > latency tool screenshot button would save to ~ or ~/Downloads by > default. > My recollection was that it was at least 10x worse before tuning. That processor only has 2 cores, even your screenshot says "2 cores". If you disabled hyperthreading as per the guide that isolcpus cmd line effectively does nothing. I would try either with hyperthreading (that shouldn't affect anything in the 100µs range) enabled or with isolcpus=1. FWIW I'm using intel N100 "firewall appliance" 4×ethernet mini-PCs with ethernet mesa hardware, don't have any latency numbers handy, but runs w/o problems. regards Robert
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