linux-kernel - Re: [PATCH] kprobes: Fix to delay the kprobes jump optimization

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Date:   Fri, 19 Feb 2021 11:45:39 -0800
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Uladzislau Rezki <urezki@...il.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>, RCU <rcu@...r.kernel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Daniel Axtens <dja@...ens.net>,
        Frederic Weisbecker <frederic@...nel.org>,
        Neeraj Upadhyay <neeraju@...eaurora.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Michal Hocko <mhocko@...e.com>,
        "Theodore Y . Ts'o" <tytso@....edu>,
        Oleksiy Avramchenko <oleksiy.avramchenko@...ymobile.com>
Subject: Re: [PATCH] kprobes: Fix to delay the kprobes jump optimization

On Fri, Feb 19, 2021 at 02:14:29PM -0500, Steven Rostedt wrote:
> On Fri, 19 Feb 2021 10:18:11 -0800
> "Paul E. McKenney" <paulmck@...nel.org> wrote:
> 
> > We can further prevent entry into dyntick-idle state until
> > the ksoftirqd kthreads have been spawned, which means that if softirq
> > handlers must be deferred, they will be resumed within one jiffy by the
> > next scheduler-clock interrupt.
> 
> Why not just prevent entry into dyntick-idle state until the system is
> finished booting? As you said; There should be no latency-sensitive
> applications running, until after we started the system.

Exactly, and that is the effect of patch to rcu_needs_cpu() that I just
now posted.

Ah, your point is that if the tick keeps running, there is no need to
modify softirq?  Good point, and I will test that, thank you!!!

							Thanx, Paul