From: Neeraj Upadhyay <quic_neeraju@quicinc.com>
To: "Paul E. McKenney" <paulmck@kernel.org>, <rcu@vger.kernel.org>
Cc: <linux-kernel@vger.kernel.org>, <kernel-team@fb.com>,
<rostedt@goodmis.org>, Zqiang <qiang1.zhang@intel.com>
Subject: Re: [PATCH rcu 08/12] rcu: Cleanup RCU urgency state for offline CPU
Date: Tue, 21 Jun 2022 12:33:12 +0530 [thread overview]
Message-ID: <5fa27044-9515-f8fa-511c-64014479e875@quicinc.com> (raw)
In-Reply-To: <20220620222032.3839547-8-paulmck@kernel.org>
On 6/21/2022 3:50 AM, Paul E. McKenney wrote:
> From: Zqiang <qiang1.zhang@intel.com>
>
> When a CPU is slow to provide a quiescent state for a given grace
> period, RCU takes steps to encourage that CPU to get with the
> quiescent-state program in a more timely fashion. These steps
> include these flags in the rcu_data structure:
>
> 1. ->rcu_urgent_qs, which causes the scheduling-clock interrupt to
> request an otherwise pointless context switch from the scheduler.
>
> 2. ->rcu_need_heavy_qs, which causes both cond_resched() and RCU's
> context-switch hook to do an immediate momentary quiscent state.
>
> 3. ->rcu_need_heavy_qs, which causes the scheduler-clock tick to
nit: s/->rcu_need_heavy_qs/->rcu_forced_tick/ ?
> be enabled even on nohz_full CPUs with only one runnable task.
>
> These flags are of course cleared once the corresponding CPU has passed
> through a quiescent state. Unless that quiescent state is the CPU
> going offline, which means that when the CPU comes back online, it will
> needlessly consume additional CPU time and incur additional latency,
> which constitutes a minor but very real performance bug.
>
> This commit therefore adds the call to rcu_disable_urgency_upon_qs()
> that clears these flags to the CPU-hotplug offlining code path.
>
> Signed-off-by: Zqiang <qiang1.zhang@intel.com>
> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
> ---
Reviewed-by: Neeraj Upadhyay <quic_neeraju@quicinc.com>
Thanks
Neeraj
> kernel/rcu/tree.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index f4a37f2032664..5445b19b48408 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -4446,6 +4446,7 @@ void rcu_report_dead(unsigned int cpu)
> rdp->rcu_ofl_gp_flags = READ_ONCE(rcu_state.gp_flags);
> if (rnp->qsmask & mask) { /* RCU waiting on outgoing CPU? */
> /* Report quiescent state -before- changing ->qsmaskinitnext! */
> + rcu_disable_urgency_upon_qs(rdp);
> rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
> raw_spin_lock_irqsave_rcu_node(rnp, flags);
> }
next prev parent reply other threads:[~2022-06-21 7:03 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-20 22:20 [PATCH rcu 0/12] Miscellaneous fixes for v5.20 Paul E. McKenney
2022-06-20 22:20 ` [PATCH rcu 01/12] rcu: Decrease FQS scan wait time in case of callback overloading Paul E. McKenney
2022-06-21 5:29 ` Neeraj Upadhyay
2022-06-21 22:19 ` Paul E. McKenney
2022-06-22 11:46 ` Neeraj Upadhyay
2022-06-20 22:20 ` [PATCH rcu 02/12] rcu: Avoid tracing a few functions executed in stop machine Paul E. McKenney
2022-06-21 5:47 ` Neeraj Upadhyay
2022-06-21 22:21 ` Paul E. McKenney
2022-06-22 11:50 ` Neeraj Upadhyay
2022-06-22 15:35 ` Paul E. McKenney
2022-06-22 15:49 ` Neeraj Upadhyay
2022-06-23 0:29 ` Paul E. McKenney
2022-06-20 22:20 ` [PATCH rcu 03/12] rcu: Add rnp->cbovldmask check in rcutree_migrate_callbacks() Paul E. McKenney
2022-06-21 5:57 ` Neeraj Upadhyay
2022-06-21 22:22 ` Paul E. McKenney
2022-06-20 22:20 ` [PATCH rcu 04/12] rcu: Immediately boost preempted readers for strict grace periods Paul E. McKenney
2022-06-21 6:00 ` Neeraj Upadhyay
2022-06-20 22:20 ` [PATCH rcu 05/12] rcu: Forbid RCU_STRICT_GRACE_PERIOD in TINY_RCU kernels Paul E. McKenney
2022-06-21 6:02 ` Neeraj Upadhyay
2022-06-20 22:20 ` [PATCH rcu 06/12] locking/csd_lock: Change csdlock_debug from early_param to __setup Paul E. McKenney
2022-06-20 22:20 ` [PATCH rcu 07/12] rcu: tiny: Record kvfree_call_rcu() call stack for KASAN Paul E. McKenney
2022-06-21 6:31 ` Neeraj Upadhyay
2022-06-21 19:31 ` Paul E. McKenney
2022-06-21 21:14 ` Marco Elver
2022-06-21 22:17 ` Paul E. McKenney
2022-06-20 22:20 ` [PATCH rcu 08/12] rcu: Cleanup RCU urgency state for offline CPU Paul E. McKenney
2022-06-21 7:03 ` Neeraj Upadhyay [this message]
2022-06-21 22:24 ` Paul E. McKenney
2022-06-20 22:20 ` [PATCH rcu 09/12] rcu/kvfree: Remove useless monitor_todo flag Paul E. McKenney
2022-06-21 10:02 ` Neeraj Upadhyay
2022-06-20 22:20 ` [PATCH rcu 10/12] rcu: Initialize first_gp_fqs at declaration in rcu_gp_fqs() Paul E. McKenney
2022-06-20 22:20 ` [PATCH rcu 11/12] rcu/tree: Add comment to describe GP-done condition in fqs loop Paul E. McKenney
2022-06-20 22:20 ` [PATCH rcu 12/12] srcu: Block less aggressively for expedited grace periods Paul E. McKenney
2022-06-21 2:00 ` Zhangfei Gao
2022-06-21 3:15 ` Paul E. McKenney
2022-06-21 7:43 ` Shameerali Kolothum Thodi
2022-06-21 19:36 ` Paul E. McKenney
2022-06-21 10:13 ` Neeraj Upadhyay
2022-06-21 22:25 ` 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:
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=5fa27044-9515-f8fa-511c-64014479e875@quicinc.com \
--to=quic_neeraju@quicinc.com \
--cc=kernel-team@fb.com \
--cc=linux-kernel@vger.kernel.org \
--cc=paulmck@kernel.org \
--cc=qiang1.zhang@intel.com \
--cc=rcu@vger.kernel.org \
--cc=rostedt@goodmis.org \
/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).