rcu.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Frederic Weisbecker <frederic@kernel.org>
To: "Paul E . McKenney" <paulmck@kernel.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
	Frederic Weisbecker <frederic@kernel.org>,
	rcu@vger.kernel.org, urezki@gmail.com, boqun.feng@gmail.com,
	Neeraj Upadhyay <neeraju@codeaurora.org>,
Subject: [PATCH 1/4] rcu: Ignore rdp.cpu_no_qs.b.exp on premptible RCU's rcu_qs()
Date: Thu, 16 Sep 2021 14:10:45 +0200	[thread overview]
Message-ID: <20210916121048.36623-2-frederic@kernel.org> (raw)
In-Reply-To: <20210916121048.36623-1-frederic@kernel.org>

The preemptible RCU flavour doesn't rely at all on
struct rcu_data::cpu_no_qs::b::exp and use its own
struct rcu_data::exp_deferred_qs field to record the need for an
expedited quiescent state.

In fact rdp.cpu_no_qs.b.exp should never be set in preemptible RCU.

Make that fact clear and disambiguate the expectations on the
preemptible RCU's rcu_qs() implementation. In this flavour, common
quiescent states aren't expected to deal with expedited grace periods
because those have their own way to report expedited quiescent states:
rcu_read_unlock_special, context switches, etc...

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
 kernel/rcu/tree_plugin.h | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 1a6fdb03d0a5..4c9aeabec242 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -277,12 +277,16 @@ static void rcu_preempt_ctxt_queue(struct rcu_node *rnp, struct rcu_data *rdp)
  * current task, there might be any number of other tasks blocked while
  * in an RCU read-side critical section.
+ * Unlike non-preemptible-RCU, quiescent state reports for expedited
+ * grace periods are handled seperately via deferred quiescent states
+ * and context switch events.
+ *
  * Callers to this function must disable preemption.
 static void rcu_qs(void)
 	RCU_LOCKDEP_WARN(preemptible(), "rcu_qs() invoked with preemption enabled!!!\n");
-	if (__this_cpu_read(rcu_data.cpu_no_qs.s)) {
+	if (__this_cpu_read(rcu_data.cpu_no_qs.b.norm)) {

  reply	other threads:[~2021-09-16 12:10 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-16 12:10 [PATCH 0/4] rcu: Unify a bit [non-]PREEMPT expedited quiescent state report Frederic Weisbecker
2021-09-16 12:10 ` Frederic Weisbecker [this message]
2021-09-16 12:10 ` [PATCH 2/4] rcu: Remove useless WRITE_ONCE() on rcu_data.exp_deferred_qs Frederic Weisbecker
2021-09-16 16:43   ` Paul E. McKenney
2021-09-16 21:05     ` Frederic Weisbecker
2021-09-17 18:10       ` Paul E. McKenney
2021-09-17 22:00         ` Frederic Weisbecker
2021-09-16 12:10 ` [PATCH 3/4] rcu: Move rcu_data.cpu_no_qs.b.exp reset to rcu_export_exp_rdp() Frederic Weisbecker
2021-09-16 12:10 ` [PATCH 4/4] rcu: Remove rcu_data.exp_deferred_qs and convert to rcu_data.cpu no_qs.b.exp Frederic Weisbecker
2021-09-16 16:40 ` [PATCH 0/4] rcu: Unify a bit [non-]PREEMPT expedited quiescent state report Paul E. McKenney
2021-09-28 18:13 ` Paul E. McKenney

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:

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

  git send-email \
    --in-reply-to=20210916121048.36623-2-frederic@kernel.org \
    --to=frederic@kernel.org \
    --cc=boqun.feng@gmail.com \
    --cc=joel@joelfernandes.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=neeraju@codeaurora.org \
    --cc=paulmck@kernel.org \
    --cc=rcu@vger.kernel.org \
    --cc=urezki@gmail.com \
    --subject='Re: [PATCH 1/4] rcu: Ignore rdp.cpu_no_qs.b.exp on premptible RCU'\''s rcu_qs()' \


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

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).