linux-kernel - Re: [RFC PATCH V4] sched: psi: Add psi events trace point

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Message-ID: <CAJuCfpE_aZKFB8O=KPq5uTv=WeJf6TCmneMnr8pp88SNWy3K-Q@mail.gmail.com>
Date: Mon, 29 Sep 2025 16:17:12 -0700
From: Suren Baghdasaryan <surenb@...gle.com>
To: Xuewen Yan <xuewen.yan@...soc.com>
Cc: hannes@...xchg.org, mathieu.desnoyers@...icios.com, mhiramat@...nel.org, 
	rostedt@...dmis.org, peterz@...radead.org, mingo@...hat.com, 
	juri.lelli@...hat.com, vincent.guittot@...aro.org, dietmar.eggemann@....com, 
	bsegall@...gle.com, mgorman@...e.de, vschneid@...hat.com, 
	linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org, 
	ke.wang@...soc.com, yuming.han@...soc.com, xuewen.yan94@...il.com, 
	Roman Gushchin <roman.gushchin@...ux.dev>
Subject: Re: [RFC PATCH V4] sched: psi: Add psi events trace point

On Sun, Sep 28, 2025 at 6:43 PM Xuewen Yan <xuewen.yan@...soc.com> wrote:
>
> Add trace point to psi triggers. This is useful to
> observe the psi events in the kernel space.
>
> One use of this is to monitor memory pressure.
> When the pressure is too high, we can kill the process
> in the kernel space to prevent OOM.

Just FYI, Roman is working on a BPF-based oom-killer solution [1]
which might be also interesting for you and this tracepoint might be
useful for Roman as well. CC'ing him here.

[1] https://lore.kernel.org/all/20250818170136.209169-1-roman.gushchin@linux.dev/
>
> Signed-off-by: Xuewen Yan <xuewen.yan@...soc.com>

Acked-by: Suren Baghdasaryan <surenb@...gle.com>

> ---
> V4:
> -generate the event only after cmpxchg() passes the check
> ---
> V3:
> -export it in the tracefs;
> ---
> v2:
> -fix compilation error;
> -export the tp;
> -add more commit message;
> ---
>  include/trace/events/sched.h | 27 +++++++++++++++++++++++++++
>  kernel/sched/psi.c           |  5 +++++
>  2 files changed, 32 insertions(+)
>
> diff --git a/include/trace/events/sched.h b/include/trace/events/sched.h
> index 7b2645b50e78..db8b8f25466e 100644
> --- a/include/trace/events/sched.h
> +++ b/include/trace/events/sched.h
> @@ -826,6 +826,33 @@ TRACE_EVENT(sched_wake_idle_without_ipi,
>         TP_printk("cpu=%d", __entry->cpu)
>  );
>
> +#ifdef CONFIG_PSI
> +TRACE_EVENT(psi_event,
> +
> +       TP_PROTO(int aggregator, int state, u64 threshold, u64 win_size),
> +
> +       TP_ARGS(aggregator, state, threshold, win_size),
> +
> +       TP_STRUCT__entry(
> +               __field(int,    aggregator)
> +               __field(int,    state)
> +               __field(u64,    threshold)
> +               __field(u64,    win_size)
> +       ),
> +
> +       TP_fast_assign(
> +               __entry->aggregator     = aggregator;
> +               __entry->state          = state;
> +               __entry->threshold      = threshold;
> +               __entry->win_size       = win_size;
> +       ),
> +
> +       TP_printk("aggregator=%d state=%d threshold=%llu window_size=%llu",
> +               __entry->aggregator, __entry->state, __entry->threshold,
> +               __entry->win_size)
> +);
> +#endif /* CONFIG_PSI */
> +
>  /*
>   * Following tracepoints are not exported in tracefs and provide hooking
>   * mechanisms only for testing and debugging purposes.
> diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
> index 59fdb7ebbf22..e8a7fd04ba9f 100644
> --- a/kernel/sched/psi.c
> +++ b/kernel/sched/psi.c
> @@ -141,6 +141,8 @@
>  #include <linux/psi.h>
>  #include "sched.h"
>
> +EXPORT_TRACEPOINT_SYMBOL_GPL(psi_event);
> +
>  static int psi_bug __read_mostly;
>
>  DEFINE_STATIC_KEY_FALSE(psi_disabled);
> @@ -515,6 +517,9 @@ static void update_triggers(struct psi_group *group, u64 now,
>                                 kernfs_notify(t->of->kn);
>                         else
>                                 wake_up_interruptible(&t->event_wait);
> +
> +                       trace_psi_event(aggregator, t->state, t->threshold,
> +                                       t->win.size);
>                 }
>                 t->last_event_time = now;
>                 /* Reset threshold breach flag once event got generated */
> --
> 2.25.1
>
>