Hello, I was surprised to notice that when I change the HZ value in a patched preempt-rt kernel from 250Hz to 1000Hz, the system load apparently drops. On my setup (x86_64, 24 vcores, hosting a few kvm guests, some ceph services, pacemaker/corosync, ovs, etc.): - kernel with RT patch, CONFIG_HZ=1000: system load is between 1 and 1.5 - kernel with RT patch, CONFIG_HZ=250: system load is between 3 and 3.5 And just in case it helps: - kernel without RT patch, CONFIG_HZ=250: system load is between 1 and 1.5 The rest of the system does not change, I'm just switching kernels for which there is only this config_hz modification... I tried this on 5.10rt, 5.15rt, 5.16rt... Everytime I try to list the runnable/uninterruptible processes (ps -A r), I see nothing, which makes me think this comes from the kernel but how exactly, I have no clue (htop showing kernel threads does not really show any differences). Does anyone know how CONFIG_HZ can impact system load on a RT kernel? Is it a "real" system load increase that will impact the performance of my system or just a by-product of how it's calculted maybe? It is maybe something to be expected to improve latency? Thanks.
