Created attachment 411772 [details] Working 4.0.4 config When upgrading the kernel on my system from 4.0.4 to 4.2.0-r1 all processes wound up tied to core 0. The 4.2.0-r1 config was created by running make old config. In an attempt to track down what changed I did experiment and prune the 4.2.0-r1 kernel and tracked it down to some changes in kernel/cpuset.c (At least that's what led me to the problem). With NOHZ_FULL enabled in the 4.2.0-r1 kernel processors appear to be "isolated" which seems to prevent processes from moving between cores. I can create other cpusets and move tasks into the explicitly but, those sets also limit processes to the first core in the cpuset. Setting NOHZ_IDLE appears to alleviate the problem. Using the nohz_full kernel command line argument to limit which cpus are running tickless also seems to work.
Created attachment 411774 [details] Brokeb 4.2.0-r1 config
Created attachment 411776 [details] emerge --info
Same problem here. Already reported on the kernel bugtracker; https://bugzilla.kernel.org/show_bug.cgi?id=104111
Upstream reports this as expected behavior but with a potential rethink. We'll follow the upstream bug in case anything changes, but there's nothing left for us to do here.
