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?) Balbir Singh.
