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TL;DR: Isolcpus Workstation Experiment Gkrellm Screenshots

isolcpus is a Linux kernel boot parameter that tells the kernel to exclude the specified CPUs from consideration for user processes. The kernel still uses it, so it's a neat way to reserve CPUs for an application (e.g. latency-sensitive) or just the kernel itself (which is interesting on very high IO workloads).

Try booting one of your Linux machines with isolcpus=0 or isolcpus=0,1 if you have a hyperthreading (Intel) CPU. On Debian variants you'll want to put it in /etc/defaults/grub. I'm running Arch so I have the following in my /boot/syslinux/syslinux.cfg

LABEL arch
    MENU LABEL Arch Linux
    LINUX ../vmlinuz-linux
    APPEND root=LABEL=NEWROOT rw isolcpus=0,1
    INITRD ../initramfs-linux.img

I've been running with this enabled on my daily driver workstation and I feel like system responsiveness is considerably better. This is all seat-of-your-pants performance measurement at the moment. I suspect this is something that will be useful in many more situations than it's used currently.

Here's what my system load looks like in gkrellm at the moment:


This is cool because most of the kernel work is happening on the first core. The isolcpus=0,1 parameter has instructed the kernel to not schedule userland processes on it. It can still schedule kernel threads on it, and lookie there, it's always idle so there's rarely any wait for CPU time and the caches aren't constantly bombarded.

And here it is with Team Fortress 2 running, because science! You can see the bouncing thread problem in the CPU graphs. Open the full screen image to see my ZFS disks heating up while TF2 loads up its resources.


More to come!