On 2020/11/23 12:38, Balbir Singh wrote: > On Tue, Nov 17, 2020 at 06:19:43PM -0500, Joel Fernandes (Google) wrote: >> From: Peter Zijlstra <pet...@infradead.org> >> >> When a sibling is forced-idle to match the core-cookie; search for >> matching tasks to fill the core. >> >> rcu_read_unlock() can incur an infrequent deadlock in >> sched_core_balance(). Fix this by using the RCU-sched flavor instead. >> > ... >> + >> + if (p->core_occupation > dst->idle->core_occupation) >> + goto next; >> + > > I am unable to understand this check, a comment or clarification in the > changelog will help. I presume we are looking at either one or two cpus > to define the core_occupation and we expect to match it against the > destination CPU.
IIUC, this check prevents a task from keeping jumping among the cores forever. For example, on a SMT2 platform: - core0 runs taskA and taskB, core_occupation is 2 - core1 runs taskC, core_occupation is 1 Without this check, taskB could ping-pong between core0 and core1 by core load balance. Thanks, -Aubrey
