From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Boqun Feng <boqun.feng@gmail.com>
Cc: "Paul E. McKenney" <paulmck@linux.ibm.com>,
Tejun Heo <tj@kernel.org>,
linux-kernel@vger.kernel.org,
Peter Zijlstra <peterz@infradead.org>,
"Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>,
tglx@linutronix.de, Steven Rostedt <rostedt@goodmis.org>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Lai Jiangshan <jiangshanlai@gmail.com>
Subject: Re: [PATCH] rcu: Use cpus_read_lock() while looking at cpu_online_mask
Date: Mon, 15 Oct 2018 17:09:03 +0200 [thread overview]
Message-ID: <20181015150902.asifwhikqkz53ai4@linutronix.de> (raw)
In-Reply-To: <20181015150715.GA2422@tardis>
On 2018-10-15 23:07:15 [+0800], Boqun Feng wrote:
> Hi, Sebastian
Hi Boqun,
> On Mon, Oct 15, 2018 at 04:42:17PM +0200, Sebastian Andrzej Siewior wrote:
> > On 2018-10-13 06:48:13 [-0700], Paul E. McKenney wrote:
> > >
> > > My concern would be that it would queue it by default for the current
> > > CPU, which would serialize the processing, losing the concurrency of
> > > grace-period initialization. But that was a long time ago, and perhaps
> > > workqueues have changed.
> >
> > but the code here is always using the first CPU of a NUMA node or did I
> > miss something?
> >
>
> The thing is the original way is to pick one CPU for a *RCU* node to
> run the grace-period work, but with your proposal, if a RCU node is
> smaller than a NUMA node (having fewer CPUs), we could end up having two
> grace-period works running on one CPU. I think that's Paul's concern.
Ah. Okay. From what I observed, the RCU nodes and NUMA nodes were 1:1
here. Noted.
Given that I can enqueue a work item on an offlined CPU I don't see why
commit fcc6354365015 ("rcu: Make expedited GPs handle CPU 0 being
offline") should make a difference. Any objections to just revert it?
> Regards,
> Boqun
Sebastian
next prev parent reply other threads:[~2018-10-15 15:09 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-10 13:56 [PATCH] rcu: Use cpus_read_lock() while looking at cpu_online_mask Sebastian Andrzej Siewior
2018-09-11 16:05 ` Paul E. McKenney
2018-09-11 16:21 ` Sebastian Andrzej Siewior
2018-09-11 17:02 ` Paul E. McKenney
2018-09-19 20:55 ` Tejun Heo
2018-09-19 22:11 ` Paul E. McKenney
2018-10-12 18:41 ` Sebastian Andrzej Siewior
2018-10-13 13:48 ` Paul E. McKenney
2018-10-15 14:42 ` Sebastian Andrzej Siewior
2018-10-15 15:07 ` Boqun Feng
2018-10-15 15:09 ` Sebastian Andrzej Siewior [this message]
2018-10-15 15:33 ` Boqun Feng
2018-10-15 16:36 ` Paul E. McKenney
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