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

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Message-ID: <CAJuCfpF6sakmsDeqrVTxwqUjRtid-7oG9KjGSQYmb0R=BCp9zw@mail.gmail.com>
Date: Wed, 29 Oct 2025 07:50:42 -0700
From: Suren Baghdasaryan <surenb@...gle.com>
To: peterz@...radead.org, hannes@...xchg.org, 
	Xuewen Yan <xuewen.yan94@...il.com>
Cc: Xuewen Yan <xuewen.yan@...soc.com>, mathieu.desnoyers@...icios.com, 
	mhiramat@...nel.org, rostedt@...dmis.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 Wed, Oct 29, 2025 at 1:53 AM Xuewen Yan <xuewen.yan94@...il.com> wrote:
>
> Gentle ping....
>
> Sorry to ask, but may I know if this patch can be merged into the mainline?

Hi Peter,
If you have no objections to this patch, could you please accept it
into your tree?
Thanks,
Suren.

>
> Thanks!
>
> 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/
> > >
> > > 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
> > >
> > >