Linux-rt-users archive on lore.kernel.org
 help / color / Atom feed
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Joel Fernandes <joel@joelfernandes.org>
Cc: "Paul E. McKenney" <paulmck@kernel.org>,
	Josh Triplett <josh@joshtriplett.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
	Lai Jiangshan <jiangshanlai@gmail.com>,
	Thomas Glexiner <tglx@linutronix.de>,
	Scott Wood <swood@redhat.com>,
	Clark Williams <williams@redhat.com>,
	Juri Lelli <juri.lelli@redhat.com>,
	linux-rt-users@vger.kernel.org, rcu <rcu@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Ingo Molnar <mingo@kernel.org>
Subject: Re: RCU use of swait
Date: Thu, 19 Mar 2020 10:25:40 +0100
Message-ID: <20200319092540.gpgzx2qao3r4okql@linutronix.de> (raw)
In-Reply-To: <CAEXW_YSiKrT50mTR1a4tB5x_jQzZKnuAo6JY-Vc5w7r=XLv+OA@mail.gmail.com>

On 2020-03-18 20:47:18 [-0400], Joel Fernandes wrote:
> In RCU, there are some truly-atomic code sections containing an
> swake_upXX() call, which would be considered atomic also on
> PREEMPT_RT, one example is:
> 
> rcu_core() contains an local_irq_{save,restore}() section.
> 
>         /* No grace period and unregistered callbacks? */
>         if (!rcu_gp_in_progress() &&
>             rcu_segcblist_is_enabled(&rdp->cblist) && !offloaded) {
>                 local_irq_save(flags);
>                 if (!rcu_segcblist_restempty(&rdp->cblist, RCU_NEXT_READY_TAIL))
>                         rcu_accelerate_cbs_unlocked(rnp, rdp);
>                 local_irq_restore(flags);
>         }
> 
> And rcu_accelerate_cbs_unlocked(rnp, rdp) calls rcu_gp_kthread_wake()
> which does an swake_up_one(), so I think we will have to leave it as
> swake_up() the way it is.

There is also this:
irq_exit()
 rcu_irq_exit()
  rcu_nmi_exit_common(true);
   rcu_prepare_for_idle()
    if (rcu_segcblist_pend_cbs(&rdp->cblist))
      rcu_gp_kthread_wake()
       swake_up_one(&rcu_state.gp_wq);

So I *think* this is another one.

> thanks,
> 
>  - Joel

Sebastian

      reply index

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-05  0:35 Paul E. McKenney
2020-03-05  8:11 ` Sebastian Andrzej Siewior
2020-03-19  0:47   ` Joel Fernandes
2020-03-19  9:25     ` Sebastian Andrzej Siewior [this message]

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20200319092540.gpgzx2qao3r4okql@linutronix.de \
    --to=bigeasy@linutronix.de \
    --cc=jiangshanlai@gmail.com \
    --cc=joel@joelfernandes.org \
    --cc=josh@joshtriplett.org \
    --cc=juri.lelli@redhat.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-rt-users@vger.kernel.org \
    --cc=mathieu.desnoyers@efficios.com \
    --cc=mingo@kernel.org \
    --cc=paulmck@kernel.org \
    --cc=rcu@vger.kernel.org \
    --cc=rostedt@goodmis.org \
    --cc=swood@redhat.com \
    --cc=tglx@linutronix.de \
    --cc=williams@redhat.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Linux-rt-users archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-rt-users/0 linux-rt-users/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-rt-users linux-rt-users/ https://lore.kernel.org/linux-rt-users \
		linux-rt-users@vger.kernel.org
	public-inbox-index linux-rt-users

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-rt-users


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git