On 2019/7/11 下午10:27, Peter Zijlstra wrote: [snip] >> Thus we introduce the numa cling, which try to prevent tasks leaving >> the preferred node on wakeup fast path. > > >> @@ -6195,6 +6447,13 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target) >> if ((unsigned)i < nr_cpumask_bits) >> return i; >> >> + /* >> + * Failed to find an idle cpu, wake affine may want to pull but >> + * try stay on prev-cpu when the task cling to it. >> + */ >> + if (task_numa_cling(p, cpu_to_node(prev), cpu_to_node(target))) >> + return prev; >> + >> return target; >> } > > Select idle sibling should never cross node boundaries and is thus the > entirely wrong place to fix anything. Hmm.. in our early testing the printk show both select_task_rq_fair() and task_numa_find_cpu() will call select_idle_sibling with prev and target on different node, thus we pick this point to save few lines. But if the semantics of select_idle_sibling() is to return cpu on the same node of target, what about move the logical after select_idle_sibling() for the two callers? Regards, Michael Wang >
