From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: "Paul E. McKenney" <paulmck@linux.ibm.com>
Cc: tglx@linutronix.de, linux-rt-users@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: rcu: Merge RCU-bh into RCU-preempt
Date: Thu, 8 Nov 2018 18:15:16 +0100 [thread overview]
Message-ID: <20181108171516.axwvjtgay4zolc56@linutronix.de> (raw)
In-Reply-To: <20181108164247.GL4170@linux.ibm.com>
On 2018-11-08 08:42:47 [-0800], Paul E. McKenney wrote:
> On Thu, Nov 08, 2018 at 05:02:57PM +0100, Sebastian Andrzej Siewior wrote:
> > On 2018-11-01 16:18:04 [-0700], Paul E. McKenney wrote:
> > > The need for this goes away as of the current merge window because
> > > RCU-bh has gone away. (Aside from still being able to do things
> > > like rcu_read_lock_bh() as a documentation device.)
> >
> > So in -RT rcu_read_lock_bh() does
> > { local_bh_disable() ; rcu_read_lock() }
> >
> > So you are saying that this is also the case in v4.20?
>
> No, rcu_read_lock_bh() and rcu_read_unlock_bh() are unchanged in v4.20.
> With the new RCU grace-period mechanism, local_bh_disable() blocks future
> grace periods on its own.
>
> Unless I am missing something (quite probable, actually), the v4.20
> definitions of rcu_read_lock_bh() and rcu_read_unlock_bh() should work
> as-is for -rt.
I *think* tglx made this patch, then you somehow reverted it partly [0]
and the final piece we need for RT is this gem:
https://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git/tree/patches/rcu-Eliminate-softirq-processing-from-rcutree.patch?h=linux-4.19.y-rt-patches
[0] rcu: Make ksoftirqd do RCU quiescent states
https://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git/tree/patches/patch-to-introduce-rcu-bh-qs-where-safe-from-softirq.patch?h=linux-4.19.y-rt-patches
> Thanx, Paul
Sebastian
next prev parent reply other threads:[~2018-11-08 17:15 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-01 23:18 rcu: Merge RCU-bh into RCU-preempt Paul E. McKenney
2018-11-08 16:02 ` Sebastian Andrzej Siewior
2018-11-08 16:42 ` Paul E. McKenney
2018-11-08 17:15 ` Sebastian Andrzej Siewior [this message]
2018-11-08 17:35 ` Paul E. McKenney
2018-11-08 17:48 ` Sebastian Andrzej Siewior
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