Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
References: <20220809034517.3867176-1-joel@joelfernandes.org>
 <20220809034517.3867176-5-joel@joelfernandes.org> <CAEXW_YQuGga9Eivq4G6o1XjvPn-nMMDiM8FOY6HXJTMzwv1Emg@mail.gmail.com>
 <CAEXW_YQOXBRwCLZXjspXttGkNhbJK3HGVDuYj5TcYD=Xj1cK0A@mail.gmail.com>
 <CAEXW_YT3VnK5KJTbyXdCzs8j4jw9XFTSCF4Dt9QwLPtkPSb1tA@mail.gmail.com>
 <20220819023550.GN2125313@paulmck-ThinkPad-P17-Gen-1> <4deb7354-bac7-b530-47ba-54cf50cfce58@joelfernandes.org>
 <2d56e4ad-7d6e-2abb-461f-15f20128d42b@joelfernandes.org> <20220819171249.GP2125313@paulmck-ThinkPad-P17-Gen-1>
 <fa8b7857-b9fd-72ad-36a7-8b09e4472816@joelfernandes.org>
In-Reply-To: <fa8b7857-b9fd-72ad-36a7-8b09e4472816@joelfernandes.org>
From:   Joel Fernandes <joel@joelfernandes.org>
Date:   Fri, 19 Aug 2022 14:17:32 -0400
Message-ID: <CAEXW_YTxtfbbQ_rOiSbu62GpDPBDFpfWrNBef06MAkYPybNJ2A@mail.gmail.com>
Subject: Re: [PATCH v3 resend 4/6] fs: Move call_rcu() to call_rcu_lazy() in
 some paths
To:     "Paul E. McKenney" <paulmck@kernel.org>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        Rushikesh S Kadam <rushikesh.s.kadam@intel.com>,
        "Uladzislau Rezki (Sony)" <urezki@gmail.com>,
        Neeraj upadhyay <neeraj.iitr10@gmail.com>,
        Frederic Weisbecker <frederic@kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>, rcu <rcu@vger.kernel.org>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Fri, Aug 19, 2022 at 2:14 PM Joel Fernandes <joel@joelfernandes.org> wrote:
[..]
> >> Things are much better with the following change. However, this brings
> >> me to a question about lock-contention based or any deferring and boot time.
> >>
> >> If you have a path like selinux doing a synchronize_rcu(), shouldn't we
> >> skip the jiffie waiting for the bypass timer? Otherwise things
> >> synchronously waiting will slow down more than usual. Maybe bypassing
> >> should not be done for any case until boot up is done. I'm curious to
> >> see if that improves boot time.
> >
> > Why not simply disable laziness at boot time and enable it only after
> > booting is complete?  The exiting rcupdate.rcu_normal_after_boot kernel
> > boot parameter uses a similar scheme.
>
> That sounds like the right thing to good, but unfortunately it wont help
> this problem. The boot time issue happens after init has started. So the
> OS is still "booting" even though the kernel has.
>
> Also the problem can happen after boot as well, like if RCU
> lazy/non-lazy callbacks come back to back quickly, or so.
>
> But yes nonetheless, I can see the value of disabling it till the
> in-kernel boot completets.

My mail client is acting weird. I meant to add to this, I wonder if
there is a way other subsystems detect when userspace boots using some
heuristic?

Thanks,

 -  Joel