Hi Chengming,
Thanks for incorporating all the feedback. I have a few nitpicks
below, but with those considered, please add:
Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
On Wed, Aug 24, 2022 at 04:18:29PM +0800, Chengming Zhou wrote:
> @@ -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().
> @@ -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.
> @@ -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.
> + 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
