On 5/20/20 1:41 PM, Thomas Gleixner wrote: > Jens Axboe <axboe@xxxxxxxxx> writes: >> On 5/20/20 8:45 AM, Jens Axboe wrote: >>> It just uses kthread_create_on_cpu(), nothing home grown. Pretty sure >>> they just break affinity if that CPU goes offline. >> >> Just checked, and it works fine for me. If I create an SQPOLL ring with >> SQ_AFF set and bound to CPU 3, if CPU 3 goes offline, then the kthread >> just appears unbound but runs just fine. When CPU 3 comes online again, >> the mask appears correct. > > When exactly during the unplug operation is it unbound? When the CPU has been fully offlined. I check the affinity mask, it reports 0. But it's still being scheduled, and it's processing work. Here's an example, PID 420 is the thread in question: [root@archlinux cpu3]# taskset -p 420 pid 420's current affinity mask: 8 [root@archlinux cpu3]# echo 0 > online [root@archlinux cpu3]# taskset -p 420 pid 420's current affinity mask: 0 [root@archlinux cpu3]# echo 1 > online [root@archlinux cpu3]# taskset -p 420 pid 420's current affinity mask: 8 So as far as I can tell, it's working fine for me with the goals I have for that kthread. -- Jens Axboe
