From: Frederic Weisbecker <frederic@kernel.org>
To: "Paul E. McKenney" <paulmck@kernel.org>
Cc: rcu@vger.kernel.org, linux-kernel@vger.kernel.org,
kernel-team@fb.com, rostedt@goodmis.org,
David Woodhouse <dwmw@amazon.co.uk>
Subject: Re: [PATCH rcu 3/9] rcu: Add mutex for rcu boost kthread spawning and affinity setting
Date: Fri, 11 Feb 2022 16:43:44 +0100 [thread overview]
Message-ID: <20220211154344.GD588079@lothringen> (raw)
In-Reply-To: <20220211154203.GB4285@paulmck-ThinkPad-P17-Gen-1>
On Fri, Feb 11, 2022 at 07:42:03AM -0800, Paul E. McKenney wrote:
> On Fri, Feb 11, 2022 at 04:11:48PM +0100, Frederic Weisbecker wrote:
> > On Fri, Feb 11, 2022 at 03:57:57PM +0100, Frederic Weisbecker wrote:
> > > On Fri, Feb 04, 2022 at 03:07:59PM -0800, Paul E. McKenney wrote:
> > > > From: David Woodhouse <dwmw@amazon.co.uk>
> > > >
> > > > As we handle parallel CPU bringup, we will need to take care to avoid
> > > > spawning multiple boost threads, or race conditions when setting their
> > > > affinity. Spotted by Paul McKenney.
> > > >
> > > > Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
> > > > Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
> > >
> > > Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
> > >
> > > Speaking of, we have:
> > >
> > > rcu_init()
> > > for_each_online_cpu(cpu) // should be boot CPU only at this stage ?
> > > rcutree_prepare_cpu(cpu)
> > > rcu_spawn_one_boost_kthread(cpu)
> > >
> > >
> > > early_initcall()
> > > rcu_spawn_gp_kthread()
> > > rcu_spawn_boost_kthreads()
> > > rcu_for_each_leaf_node(rnp)
> > > rcu_rnp_online_cpus(rnp) // as above, only boot CPU at this stage.
> > > rcu_spawn_one_boost_kthread(cpu)
> > >
> > > cpu_up()
> > > rcutree_prepare_cpu(cpu)
> > > rcu_spawn_one_boost_kthread(cpu)
> > >
> > >
> > > My guess is that we could remove rcu_spawn_boost_kthreads() and simplify
> > > rcu_init(). Something like this (untested yet):
>
> If you also add a WARN_ON() for more than one CPU being online at
> rcu_init() time, I am good with this approach. The main danger that
> the pre-rcu_init() portion of the boot time becomes the long straw in
> the eternal quest to make systems boot faster, but it is not hard to
> put it back. Hence the WARN_ON() to make it clear that adjustment
> is needed. ;-)
>
> Thanx, Paul
Make sense. On my TODO list then.
Thanks!
next prev parent reply other threads:[~2022-02-11 15:43 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-04 23:07 [PATCH rcu 0/9] Miscellaneous fixes for v5.18 Paul E. McKenney
2022-02-04 23:07 ` [PATCH rcu 1/9] MAINTAINERS: Add Frederic and Neeraj to their RCU files Paul E. McKenney
2022-02-11 15:15 ` Frederic Weisbecker
2022-02-11 16:40 ` Paul E. McKenney
2022-02-04 23:07 ` [PATCH rcu 2/9] rcu: Fix description of kvfree_rcu() Paul E. McKenney
2022-02-04 23:07 ` [PATCH rcu 3/9] rcu: Add mutex for rcu boost kthread spawning and affinity setting Paul E. McKenney
2022-02-11 14:57 ` Frederic Weisbecker
2022-02-11 15:11 ` Frederic Weisbecker
2022-02-11 15:42 ` Paul E. McKenney
2022-02-11 15:43 ` Frederic Weisbecker [this message]
2022-02-04 23:08 ` [PATCH rcu 4/9] rcu: Inline __call_rcu() into call_rcu() Paul E. McKenney
2022-02-04 23:08 ` [PATCH rcu 5/9] kasan: Record work creation stack trace with interrupts enabled Paul E. McKenney
2022-02-04 23:08 ` [PATCH rcu 6/9] rcu: Mark writes to the rcu_segcblist structure's ->flags field Paul E. McKenney
2022-02-04 23:08 ` [PATCH rcu 7/9] rcu: Uninline multi-use function: finish_rcuwait() Paul E. McKenney
2022-02-04 23:08 ` [PATCH rcu 8/9] rcu: Remove __read_mostly annotations from rcu_scheduler_active externs Paul E. McKenney
2022-02-04 23:08 ` [PATCH rcu 9/9] rcu: Replace cpumask_weight with cpumask_empty where appropriate Paul E. McKenney
2022-02-11 15:17 ` Frederic Weisbecker
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