From: "Paul E. McKenney" <paulmck@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: rcu@vger.kernel.org, linux-kernel@vger.kernel.org,
kernel-team@fb.com, mingo@kernel.org, jiangshanlai@gmail.com,
akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
josh@joshtriplett.org, tglx@linutronix.de, rostedt@goodmis.org,
dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com,
oleg@redhat.com, joel@joelfernandes.org,
Juri Lelli <juri.lelli@redhat.com>
Subject: Re: [PATCH rcu 11/14] rcu: Make rcu_normal_after_boot writable again
Date: Thu, 16 Sep 2021 09:53:24 -0700 [thread overview]
Message-ID: <20210916165324.GG4156@paulmck-ThinkPad-P17-Gen-1> (raw)
In-Reply-To: <YUNUQ564PKq9wtTF@hirez.programming.kicks-ass.net>
On Thu, Sep 16, 2021 at 04:27:15PM +0200, Peter Zijlstra wrote:
> On Thu, Sep 16, 2021 at 06:57:12AM -0700, Paul E. McKenney wrote:
> > RT systems they avoid expedited grace periods by booting with either
> > the rcupdate.rcu_normal or the rcupdate.rcu_normal_after_boot kernel
> > boot parameters. And here is the definition for the latter:
> >
> > static int rcu_normal_after_boot = IS_ENABLED(CONFIG_PREEMPT_RT);
> >
> > In other words, RT systems shut off expedited grace periods by default,
> > and are thus free to use nohz_full CPU or not, as they choose. When using
> > nohz_full, they can also enable expedited grace periods by booting with
> > rcupdate.rcu_normal_after_boot=0. Or not, sysadm's choice.
> >
> > So I am not seeing a problem here. What am I missing?
>
> That wasn't at all clear to me from the Changelog. I thought it was
> enabling expedited crud for RT.
This paragraph of the current commit log covers that point:
Make rcupdate.rcu_normal_after_boot= again writeable on RT (if
NO_HZ_ FULL is defined), but keep its default value to 1 (enabled)
to avoid regressions. Users who need synchronize_rcu_expedited()
will boot with rcupdate.rcu_normal_after_ boot=0 in the kernel
cmdline.
Does that cover it from your viewpoint? If not, any suggested changes
for clarification?
Thanx, Paul
next prev parent reply other threads:[~2021-09-16 17:52 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-15 23:33 [PATCH rcu 0/14] Miscellaneous fixes for v5.16 Paul E. McKenney
2021-09-15 23:33 ` [PATCH rcu 01/14] rcu: Mark accesses to rcu_state.n_force_qs Paul E. McKenney
2021-09-15 23:33 ` [PATCH rcu 02/14] rcu-nocb: Fix a couple of tree_nocb code-style nits Paul E. McKenney
2021-09-15 23:33 ` [PATCH rcu 03/14] rcu: Eliminate rcu_implicit_dynticks_qs() local variable rnhqp Paul E. McKenney
2021-09-15 23:33 ` [PATCH rcu 04/14] rcu: Eliminate rcu_implicit_dynticks_qs() local variable ruqp Paul E. McKenney
2021-09-15 23:33 ` [PATCH rcu 05/14] doc: Add another stall-warning root cause in stallwarn.rst Paul E. McKenney
2021-09-15 23:33 ` [PATCH rcu 06/14] rcu: Fix undefined Kconfig macros Paul E. McKenney
2021-09-15 23:33 ` [PATCH rcu 07/14] rcu: Comment rcu_gp_init() code waiting for CPU-hotplug operations Paul E. McKenney
2021-09-15 23:33 ` [PATCH rcu 08/14] rcu: Move rcu_dynticks_eqs_online() to rcu_cpu_starting() Paul E. McKenney
2021-09-15 23:33 ` [PATCH rcu 09/14] rcu: Simplify rcu_report_dead() call to rcu_report_exp_rdp() Paul E. McKenney
2021-09-15 23:33 ` [PATCH rcu 10/14] rcu: Make rcutree_dying_cpu() use its "cpu" parameter Paul E. McKenney
2021-09-16 7:28 ` Peter Zijlstra
2021-09-15 23:33 ` [PATCH rcu 11/14] rcu: Make rcu_normal_after_boot writable again Paul E. McKenney
2021-09-16 7:30 ` Peter Zijlstra
2021-09-16 13:57 ` Paul E. McKenney
2021-09-16 14:27 ` Peter Zijlstra
2021-09-16 16:53 ` Paul E. McKenney [this message]
2021-09-15 23:33 ` [PATCH rcu 12/14] rcu: Make rcu update module parameters world-readable Paul E. McKenney
2021-09-15 23:33 ` [PATCH rcu 13/14] rcu: Fix existing exp request check in sync_sched_exp_online_cleanup() Paul E. McKenney
2021-09-15 23:33 ` [PATCH rcu 14/14] rcu: Avoid unneeded function call in rcu_read_unlock() Paul E. McKenney
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