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

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Message-ID: <CAB8ipk-xw-wcCB=rSv5-aEANefww_JiB4nKRW1iFXxGOA3tW-Q@mail.gmail.com>
Date: Tue, 30 Sep 2025 11:19:14 +0800
From: Xuewen Yan <xuewen.yan94@...il.com>
To: Suren Baghdasaryan <surenb@...gle.com>
Cc: Xuewen Yan <xuewen.yan@...soc.com>, 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, 
	Roman Gushchin <roman.gushchin@...ux.dev>
Subject: Re: [RFC PATCH V4] sched: psi: Add psi events trace point

On Tue, Sep 30, 2025 at 7:17 AM Suren Baghdasaryan <surenb@...gle.com> wrote:
>
> 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/

Thanks for the review and the bpf patch, I'm interested in these.
> >
> > Signed-off-by: Xuewen Yan <xuewen.yan@...soc.com>
>
> Acked-by: Suren Baghdasaryan <surenb@...gle.com>

Thanks!
---
BR
>
> > ---
> > 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
> >
> >