On 2022/8/24 17:59, Johannes Weiner wrote:

Hi Chengming,

Thanks for incorporating all the feedback. I have a few nitpicks
below, but with those considered, please add:

Acked-by: Johannes Weiner <redacted>

On Wed, Aug 24, 2022 at 04:18:29PM +0800, Chengming Zhou wrote:

quoted

@@ -5171,12 +5220,19 @@ static struct cftype cgroup_base_files[] = {
 	{
 		.name = "irq.pressure",
 		.flags = CFTYPE_PRESSURE,
+		.file_offset = offsetof(struct cgroup, psi_files[PSI_IRQ]),
 		.seq_show = cgroup_irq_pressure_show,
 		.write = cgroup_irq_pressure_write,
 		.poll = cgroup_pressure_poll,
 		.release = cgroup_pressure_release,
 	},
 #endif
+	{
+		.name = "cgroup.pressure",
+		.flags = CFTYPE_PRESSURE,
+		.seq_show = cgroup_psi_show,
+		.write = cgroup_psi_write,

To match the naming convention, these should be called
cgroup_pressure_show() and cgroup_pressure_write().

I just find cgroup_pressure_write() already exists, so I change the names
to cgroup_pressure_enable_show() and cgroup_pressure_enable_write(),
since this file name is simplified from "cgroup.pressure.enable".

Thanks.

quoted

@@ -745,6 +745,14 @@ static void psi_group_change(struct psi_group *group, int cpu,
 		if (set & (1 << t))
 			groupc->tasks[t]++;
 
+	if (!group->enabled) {
+		if (groupc->state_mask & (1 << PSI_NONIDLE))
+			record_times(groupc, now);

Thanks for the explanation in the other thread, it made sense. But can
you please add a comment to document it? Something like:

	/*
	 * On the first group change after disabling PSI, conclude
	 * the current state and flush its time. This is unlikely
	 * to matter to the user, but aggregation (get_recent_times)
	 * may have already incorporated the live state into times_prev;
	 * avoid a delta sample underflow when PSI is later re-enabled.
	 */

An unlikely() would also make sense on that branch.

quoted

@@ -1081,6 +1092,40 @@ void cgroup_move_task(struct task_struct *task, struct css_set *to)
 
 	task_rq_unlock(rq, task, &rf);
 }
+
+void psi_cgroup_enabled_sync(struct psi_group *group)
+{
+	int cpu;
+
+	/*
+	 * After we disable psi_group->enabled, we don't actually
+	 * stop percpu tasks accounting in each psi_group_cpu,
+	 * instead only stop test_state() loop, record_times()
+	 * and averaging worker, see psi_group_change() for details.
+	 *
+	 * When disable cgroup PSI, this function has nothing to sync
+	 * since cgroup pressure files are hidden and percpu psi_group_cpu
+	 * would see !psi_group->enabled and only do task accounting.
+	 *
+	 * When re-enable cgroup PSI, this function use psi_group_change()
+	 * to get correct state mask from test_state() loop on tasks[],
+	 * and restart groupc->state_start from now, use .clear = .set = 0
+	 * here since no task status really changed.
+	 */
+	if (!group->enabled)
+		return;

Thanks for adding the comment, that's helpful.

I think the function would be a tad clearer and self-documenting if
you called it psi_cgroup_restart(), and only call it on enabling.

quoted

+	for_each_possible_cpu(cpu) {
+		struct rq *rq = cpu_rq(cpu);
+		struct rq_flags rf;
+		u64 now;
+
+		rq_lock_irq(rq, &rf);
+		now = cpu_clock(cpu);
+		psi_group_change(group, cpu, 0, 0, now, true);
+		rq_unlock_irq(rq, &rf);
+	}
+}
 #endif /* CONFIG_CGROUPS */

Thanks,
Johannes