On 2020/11/24 7:35, Balbir Singh wrote: > On Mon, Nov 23, 2020 at 11:07:27PM +0800, Li, Aubrey wrote: >> 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. > > But the comparison is p->core_occuption (as in tasks core occuptation, > not sure what that means, can a task have a core_occupation of > 1?) >
p->core_occupation is assigned to the core occupation in the last pick_next_task. (so yes, it can have a > 1 core_occupation). Thanks, -Aubrey
