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>,
Uladzislau Rezki <urezki@gmail.com>,
Neeraj Upadhyay <quic_neeraju@quicinc.com>,
Boqun Feng <boqun.feng@gmail.com>,
Josh Triplett <josh@joshtriplett.org>,
Joel Fernandes <joel@joelfernandes.org>,
rcu@vger.kernel.org
Subject: [PATCH 3/6] rcu/nocb: Optimize kthreads and rdp initialization
Date: Wed, 17 Nov 2021 16:56:34 +0100 [thread overview]
Message-ID: <20211117155637.363706-4-frederic@kernel.org> (raw)
In-Reply-To: <20211117155637.363706-1-frederic@kernel.org>
Currently cpumask_available() is used to prevent from unwanted
NOCB initialization. However if "rcu_nocbs=" isn't passed but
CONFIG_CPUMASK_OFFSTACK=n, the initialization path is still taken,
running through all sorts of needless operations and iterations on an
empty cpumask.
Fix this with relying on a real initialization state instead. This
also optimize kthreads creation, sparing iteration over all online CPUs
when nocb isn't initialized.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Neeraj Upadhyay <quic_neeraju@quicinc.com>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Uladzislau Rezki <urezki@gmail.com>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Joel Fernandes <joel@joelfernandes.org>
---
kernel/rcu/tree_nocb.h | 24 +++++++++++++++++-------
1 file changed, 17 insertions(+), 7 deletions(-)
diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h
index 0543d5e913bb..9fe4be10fde7 100644
--- a/kernel/rcu/tree_nocb.h
+++ b/kernel/rcu/tree_nocb.h
@@ -60,6 +60,9 @@ static inline bool rcu_current_is_nocb_kthread(struct rcu_data *rdp)
* Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters.
* If the list is invalid, a warning is emitted and all CPUs are offloaded.
*/
+
+static bool rcu_nocb_is_setup;
+
static int __init rcu_nocb_setup(char *str)
{
alloc_bootmem_cpumask_var(&rcu_nocb_mask);
@@ -67,6 +70,7 @@ static int __init rcu_nocb_setup(char *str)
pr_warn("rcu_nocbs= bad CPU range, all CPUs set\n");
cpumask_setall(rcu_nocb_mask);
}
+ rcu_nocb_is_setup = true;
return 1;
}
__setup("rcu_nocbs=", rcu_nocb_setup);
@@ -1151,13 +1155,17 @@ void __init rcu_init_nohz(void)
need_rcu_nocb_mask = true;
#endif /* #if defined(CONFIG_NO_HZ_FULL) */
- if (!cpumask_available(rcu_nocb_mask) && need_rcu_nocb_mask) {
- if (!zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL)) {
- pr_info("rcu_nocb_mask allocation failed, callback offloading disabled.\n");
- return;
+ if (need_rcu_nocb_mask) {
+ if (!cpumask_available(rcu_nocb_mask)) {
+ if (!zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL)) {
+ pr_info("rcu_nocb_mask allocation failed, callback offloading disabled.\n");
+ return;
+ }
}
+ rcu_nocb_is_setup = true;
}
- if (!cpumask_available(rcu_nocb_mask))
+
+ if (!rcu_nocb_is_setup)
return;
#if defined(CONFIG_NO_HZ_FULL)
@@ -1259,8 +1267,10 @@ static void __init rcu_spawn_nocb_kthreads(void)
{
int cpu;
- for_each_online_cpu(cpu)
- rcu_spawn_cpu_nocb_kthread(cpu);
+ if (rcu_nocb_is_setup) {
+ for_each_online_cpu(cpu)
+ rcu_spawn_cpu_nocb_kthread(cpu);
+ }
}
/* How many CB CPU IDs per GP kthread? Default of -1 for sqrt(nr_cpu_ids). */
--
2.25.1
next prev parent reply other threads:[~2021-11-17 15:56 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-17 15:56 [PATCH 0/6] rcu/nocb: Last prep work before cpuset interface Frederic Weisbecker
2021-11-17 15:56 ` [PATCH 1/6] rcu/nocb: Remove rdp from nocb list when de-offloaded Frederic Weisbecker
2021-11-17 18:53 ` Paul E. McKenney
2021-11-17 21:47 ` Frederic Weisbecker
2021-11-17 22:25 ` Paul E. McKenney
2021-11-17 15:56 ` [PATCH 2/6] rcu/nocb: Prepare nocb_cb_wait() to start with a non-offloaded rdp Frederic Weisbecker
2021-11-17 15:56 ` Frederic Weisbecker [this message]
2021-11-17 15:56 ` [PATCH 4/6] rcu/nocb: Create nocb kthreads on all CPUs as long as the "rcu_nocb=" is passed Frederic Weisbecker
2021-11-17 19:27 ` Paul E. McKenney
2021-11-17 21:57 ` Frederic Weisbecker
2021-11-17 22:28 ` Paul E. McKenney
2021-11-17 15:56 ` [PATCH 5/6] rcu/nocb: Allow empty "rcu_nocbs" kernel parameter Frederic Weisbecker
2021-11-17 19:46 ` Paul E. McKenney
2021-11-17 22:02 ` Frederic Weisbecker
2021-11-17 22:33 ` Paul E. McKenney
2021-11-17 15:56 ` [PATCH 6/6] rcu/nocb: Merge rcu_spawn_cpu_nocb_kthread() and rcu_spawn_one_nocb_kthread() Frederic Weisbecker
2021-11-23 0:37 [PATCH 0/6] rcu/nocb: Last prep work before cpuset interface v2 Frederic Weisbecker
2021-11-23 0:37 ` [PATCH 3/6] rcu/nocb: Optimize kthreads and rdp initialization Frederic Weisbecker
2021-11-25 0:30 ` Paul E. McKenney
2021-12-02 18:10 ` Frederic Weisbecker
2021-12-01 9:26 ` Neeraj Upadhyay
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=20211117155637.363706-4-frederic@kernel.org \
--to=frederic@kernel.org \
--cc=boqun.feng@gmail.com \
--cc=joel@joelfernandes.org \
--cc=josh@joshtriplett.org \
--cc=linux-kernel@vger.kernel.org \
--cc=paulmck@kernel.org \
--cc=quic_neeraju@quicinc.com \
--cc=rcu@vger.kernel.org \
--cc=urezki@gmail.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
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
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).