Hi Reinette, Fenghua,
On 03/12/2020 23:25, Reinette Chatre wrote:
From: Fenghua Yu fenghua.yu@intel.com
The code of setting the CPU on which a task is running in a CPU mask is moved into a couple of helpers. The new helper task_on_cpu() will be reused shortly.
diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c index 6f4ca4bea625..68db7d2dec8f 100644 --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c @@ -525,6 +525,38 @@ static void rdtgroup_remove(struct rdtgroup *rdtgrp)
+#ifdef CONFIG_SMP
(using IS_ENABLED(CONFIG_SMP) lets the compiler check all the code in one go, then dead-code-remove the stuff that will never happen... its also easier on the eye!)
+/* Get the CPU if the task is on it. */ +static bool task_on_cpu(struct task_struct *t, int *cpu) +{
- /*
* This is safe on x86 w/o barriers as the ordering of writing to* task_cpu() and t->on_cpu is reverse to the reading here. The* detection is inaccurate as tasks might move or schedule before* the smp function call takes place. In such a case the function* call is pointless, but there is no other side effect.*/
- if (t->on_cpu) {
kernel/sched/core.c calls out that there can be two tasks on one CPU with this set. (grep astute) I think that means this series will falsely match the old task for a CPU while the scheduler is running, and IPI it unnecessarily.
task_curr() is the helper that knows not to do this.
*cpu = task_cpu(t);return true;- }
- return false;
+}
Thanks,
James