Hello Vincent,
On 5/5/2025 8:40 PM, Vincent Guittot wrote:
commit 16b0a7a1a0af ("sched/fair: Ensure tasks spreading in LLC during LB") eases the spread of task inside a LLC so It's not obvious for me how it would increase "a lot of CPU migrations go out of CCX, then L3 miss,". On the other hand, it will spread task in SMT and in LLC which can prevent running at highest freq on some system but I don't know if it's relevant for this SoC.
I misspoke there. JB's workload seems to be sensitive even to core to core migrations - "relax_domain_level=2" actually disabled newidle balance above CLUSTER level which is a subset of MC on x86 and gets
Did he try with relax_domain_level=3, i.e. prevent newilde idle balance between LLC ? I don't see results showing that it's not enough to prevent newly idle migration between LLC
I don't think he did. JB if it isn't too much trouble, could you please try running with "relax_domain_level=3" in kernel cmdline and see if the performance is similar to "relax_domain_level=2".
I only realized it later that "relax_domain_level" works on topology levels before degeneration.