From: Frederic Weisbecker <frederic@kernel.org>
To: Pingfan Liu <kernelfans@gmail.com>
Cc: rcu@vger.kernel.org, "Paul E. McKenney" <paulmck@kernel.org>,
David Woodhouse <dwmw@amazon.co.uk>,
Neeraj Upadhyay <quic_neeraju@quicinc.com>,
Josh Triplett <josh@joshtriplett.org>,
Steven Rostedt <rostedt@goodmis.org>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Lai Jiangshan <jiangshanlai@gmail.com>,
Joel Fernandes <joel@joelfernandes.org>,
"Jason A. Donenfeld" <Jason@zx2c4.com>
Subject: Re: [PATCHv2 3/3] rcu: coordinate tick dependency during concurrent offlining
Date: Tue, 20 Sep 2022 11:46:45 +0200 [thread overview]
Message-ID: <20220920094645.GG69891@lothringen> (raw)
In-Reply-To: <YylrJCjYPrcT6xKJ@piliu.users.ipa.redhat.com>
On Tue, Sep 20, 2022 at 03:26:28PM +0800, Pingfan Liu wrote:
> On Fri, Sep 16, 2022 at 03:42:58PM +0200, Frederic Weisbecker wrote:
> > Note this is only locking the rdp's node, not the root node.
> > Therefore if CPU 0 and CPU 256 are going off at the same time and they
> > don't belong to the same node, the above won't protect against concurrent
> > TICK_DEP_BIT_RCU set/clear.
> >
>
> Nice, thanks for the careful thoughts. How about moving the counting
> place to the root node?
You could but then you'd need to lock the root node.
>
> > My suspicion is that we don't need this TICK_DEP_BIT_RCU tick dependency
> > anymore. I believe it was there because of issues that were fixed with:
> >
> > 53e87e3cdc15 (timers/nohz: Last resort update jiffies on nohz_full IRQ entry)
> > and:
> >
> > a1ff03cd6fb9 (tick: Detect and fix jiffies update stall)
> >
> > It's unfortunately just suspicion because the reason for that tick dependency
> > is unclear but I believe it should be safe to remove now.
> >
>
> I have gone through this tick dependency again, but got less.
>
> I think at least from the RCU's viewpoint, it is useless since
> multi_cpu_stop()->rcu_momentary_dyntick_idle() has eliminate the
> requirement for tick interrupt.
Partly yes.
> Is there a way to have a convincing test so that these code can be removed?
> Or this code will be got along with?
Hmm, Paul might remember which rcutorture scenario would trigger it?
next prev parent reply other threads:[~2022-09-20 9:46 UTC|newest]
Thread overview: 61+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-15 5:58 [PATCHv2 0/3] rcu: Enhance the capability to cope with concurrent cpu offlining/onlining Pingfan Liu
2022-09-15 5:58 ` [PATCHv2 1/3] rcu: Keep qsmaskinitnext fresh when rcutree_online_cpu() Pingfan Liu
2022-09-15 6:11 ` Pingfan Liu
2022-09-16 14:52 ` Frederic Weisbecker
2022-09-19 10:24 ` Pingfan Liu
2022-09-19 10:51 ` Frederic Weisbecker
2022-09-20 3:45 ` Pingfan Liu
2022-09-20 9:23 ` Frederic Weisbecker
2022-10-01 2:26 ` Joel Fernandes
2022-10-02 12:34 ` Pingfan Liu
2022-10-02 15:52 ` Joel Fernandes
2022-09-20 10:31 ` Frederic Weisbecker
2022-09-21 11:56 ` Pingfan Liu
2022-09-15 5:58 ` [PATCHv2 2/3] rcu: Resort to cpu_dying_mask for affinity when offlining Pingfan Liu
2022-09-16 14:23 ` Frederic Weisbecker
2022-09-19 4:33 ` Pingfan Liu
2022-09-19 10:34 ` Frederic Weisbecker
2022-09-20 3:16 ` Pingfan Liu
2022-09-20 9:00 ` Frederic Weisbecker
2022-09-20 9:38 ` Frederic Weisbecker
2022-09-21 11:48 ` Pingfan Liu
2022-09-15 5:58 ` [PATCHv2 3/3] rcu: coordinate tick dependency during concurrent offlining Pingfan Liu
2022-09-16 13:42 ` Frederic Weisbecker
2022-09-20 7:26 ` Pingfan Liu
2022-09-20 9:46 ` Frederic Weisbecker [this message]
2022-09-20 19:13 ` Paul E. McKenney
2022-09-22 9:29 ` Pingfan Liu
2022-09-22 13:54 ` Paul E. McKenney
2022-09-23 22:13 ` Frederic Weisbecker
2022-09-26 6:34 ` Pingfan Liu
2022-09-26 22:23 ` Paul E. McKenney
2022-09-27 9:59 ` Pingfan Liu
2022-09-29 8:19 ` Pingfan Liu
2022-09-29 8:20 ` Pingfan Liu
2022-09-30 13:04 ` Joel Fernandes
2022-10-02 14:06 ` Pingfan Liu
2022-10-02 16:11 ` Joel Fernandes
2022-10-02 16:24 ` Paul E. McKenney
2022-10-02 16:30 ` Joel Fernandes
2022-10-02 16:57 ` Paul E. McKenney
2022-10-02 16:59 ` Joel Fernandes
2022-09-30 15:44 ` Paul E. McKenney
2022-10-02 13:29 ` Pingfan Liu
2022-10-02 15:08 ` Frederic Weisbecker
2022-10-02 16:20 ` Paul E. McKenney
2022-10-02 16:20 ` Paul E. McKenney
[not found] ` <CAFgQCTtgLfc0NeYqyWk4Ew-pA9rMREjRjWSnQhYLv-V5117s9Q@mail.gmail.com>
2022-10-27 17:46 ` Paul E. McKenney
2022-10-31 3:24 ` Pingfan Liu
2022-11-03 16:51 ` Paul E. McKenney
2022-11-07 16:07 ` Paul E. McKenney
2022-11-09 18:55 ` Joel Fernandes
2022-11-18 12:08 ` Pingfan Liu
2022-11-18 23:30 ` Paul E. McKenney
2022-11-21 3:48 ` Pingfan Liu
2022-11-21 17:14 ` Paul E. McKenney
2022-11-17 14:39 ` Frederic Weisbecker
2022-11-18 1:45 ` Pingfan Liu
[not found] ` <CAFgQCTtNetv7v_Law=abPtngC8Gv6OGcGz9M_wWMxz_GAEWDUQ@mail.gmail.com>
2022-10-27 18:13 ` Paul E. McKenney
2022-10-31 2:10 ` Pingfan Liu
2022-09-26 16:13 ` Joel Fernandes
2022-09-27 9:42 ` Pingfan Liu
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