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Date: Wed, 8 Feb 2023 14:15:12 -0500
From: Johannes Weiner <hannes@...xchg.org>
To: Kairui Song <ryncsn@...il.com>
Cc: Suren Baghdasaryan <surenb@...gle.com>,
Chengming Zhou <zhouchengming@...edance.com>,
Michal Koutný <mkoutny@...e.com>,
Tejun Heo <tj@...nel.org>, Ingo Molnar <mingo@...hat.com>,
Peter Zijlstra <peterz@...radead.org>, cgroups@...r.kernel.org,
linux-kernel@...r.kernel.org, Kairui Song <kasong@...cent.com>
Subject: Re: [PATCH 2/2] sched/psi: iterate through cgroups directly
On Thu, Feb 09, 2023 at 12:16:54AM +0800, Kairui Song wrote:
> From: Kairui Song <kasong@...cent.com>
>
> psi_group->parent has the same hierarchy as the cgroup it's in.
> So just iterate through cgroup instead.
>
> By adjusting the iteration logic, save some space in psi_group
> struct, and the performance is actually better. I see a measurable
> performance gain using mmtests/perfpipe:
>
> (AVG of 100 test, ops/sec, the higher the better)
> KVM guest on a i7-9700:
> psi=0 root cgroup 5 levels of cgroup
> Before: 59221 55352 47821
> After: 60100 56036 50884
>
> KVM guest on a Ryzen 9 5900HX:
> psi=0 root cgroup 5 levels of cgroup
> Before: 144566 138919 128888
> After: 145812 139580 133514
>
> Signed-off-by: Kairui Song <kasong@...cent.com>
> Signed-off-by: Kairui Song <ryncsn@...il.com>
Awesome!
A few comments below:
> @@ -858,15 +858,34 @@ static void psi_group_change(struct psi_group *group, int cpu,
> schedule_delayed_work(&group->avgs_work, PSI_FREQ);
> }
>
> -static inline struct psi_group *task_psi_group(struct task_struct *task)
> +static inline struct psi_group *psi_iter_first(struct task_struct *task, void **iter)
Please name these psi_groups_first() and psi_groups_next().
> #ifdef CONFIG_CGROUPS
> - if (static_branch_likely(&psi_cgroups_enabled))
> - return cgroup_psi(task_dfl_cgroup(task));
> + if (static_branch_likely(&psi_cgroups_enabled)) {
> + struct cgroup *cgroup = task_dfl_cgroup(task);
> +
> + *iter = cgroup_parent(cgroup);
> + return cgroup_psi(cgroup);
> + }
> #endif
> return &psi_system;
> }
>
> +static inline struct psi_group *psi_iter_next(void **iter)
> +{
> +#ifdef CONFIG_CGROUPS
> + if (static_branch_likely(&psi_cgroups_enabled)) {
> + struct cgroup *cgroup = *iter;
> +
> + if (cgroup) {
> + *iter = cgroup_parent(cgroup);
> + return cgroup_psi(cgroup);
> + }
> + }
> +#endif
> + return NULL;
> +}
> @@ -886,6 +905,7 @@ void psi_task_change(struct task_struct *task, int clear, int set)
> {
> int cpu = task_cpu(task);
> struct psi_group *group;
> + void *iter;
> u64 now;
>
> if (!task->pid)
> @@ -895,16 +915,17 @@ void psi_task_change(struct task_struct *task, int clear, int set)
>
> now = cpu_clock(cpu);
>
> - group = task_psi_group(task);
> + group = psi_iter_first(task, &iter);
> do {
> psi_group_change(group, cpu, clear, set, now, true);
> - } while ((group = group->parent));
> + } while ((group = psi_iter_next(&iter)));
> }
>
> void psi_task_switch(struct task_struct *prev, struct task_struct *next,
> bool sleep)
> {
> struct psi_group *group, *common = NULL;
> + void *iter;
> int cpu = task_cpu(prev);
> u64 now = cpu_clock(cpu);
Please add @iter at the end to keep line length sorting.
> @@ -915,7 +936,7 @@ void psi_task_switch(struct task_struct *prev, struct task_struct *next,
> * ancestors with @prev, those will already have @prev's
> * TSK_ONCPU bit set, and we can stop the iteration there.
> */
> - group = task_psi_group(next);
> + group = psi_iter_first(prev, &iter);
> do {
> if (per_cpu_ptr(group->pcpu, cpu)->state_mask &
> PSI_ONCPU) {
> @@ -924,7 +945,7 @@ void psi_task_switch(struct task_struct *prev, struct task_struct *next,
> }
>
> psi_group_change(group, cpu, 0, TSK_ONCPU, now, true);
> - } while ((group = group->parent));
> + } while ((group = psi_iter_next(&iter)));
> }
>
> if (prev->pid) {
> @@ -957,12 +978,12 @@ void psi_task_switch(struct task_struct *prev, struct task_struct *next,
>
> psi_flags_change(prev, clear, set);
>
> - group = task_psi_group(prev);
> + group = psi_iter_first(prev, &iter);
> do {
> if (group == common)
> break;
> psi_group_change(group, cpu, clear, set, now, wake_clock);
> - } while ((group = group->parent));
> + } while ((group = psi_iter_next(&iter)));
>
> /*
> * TSK_ONCPU is handled up to the common ancestor. If there are
> @@ -972,7 +993,7 @@ void psi_task_switch(struct task_struct *prev, struct task_struct *next,
> */
> if ((prev->psi_flags ^ next->psi_flags) & ~TSK_ONCPU) {
> clear &= ~TSK_ONCPU;
> - for (; group; group = group->parent)
> + for (; group; group = psi_iter_next(&iter))
> psi_group_change(group, cpu, clear, set, now, wake_clock);
> }
> }
> @@ -983,6 +1004,7 @@ void psi_account_irqtime(struct task_struct *task, u32 delta)
> {
> int cpu = task_cpu(task);
> struct psi_group *group;
> + void *iter;
> struct psi_group_cpu *groupc;
> u64 now;
Ditto. You can move @groupc in the same patch.
Otherwise, this looks good to me. Please add:
Acked-by: Johannes Weiner <hannes@...xchg.org>
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