LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: "tip-bot2 for Quentin Perret" <tip-bot2@linutronix.de>
To: linux-tip-commits@vger.kernel.org
Cc: Rick Yiu <rickyiu@google.com>,
	Quentin Perret <qperret@google.com>,
	"Peter Zijlstra (Intel)" <peterz@infradead.org>,
	Qais Yousef <qais.yousef@arm.com>,
	Dietmar Eggemann <dietmar.eggemann@arm.com>,
	x86@kernel.org, linux-kernel@vger.kernel.org
Subject: [tip: sched/core] sched: Fix UCLAMP_FLAG_IDLE setting
Date: Fri, 06 Aug 2021 12:57:50 -0000	[thread overview]
Message-ID: <162825467066.395.3955621672709689514.tip-bot2@tip-bot2> (raw)
In-Reply-To: <20210805102154.590709-2-qperret@google.com>

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     ca4984a7dd863f3e1c0df775ae3e744bff24c303
Gitweb:        https://git.kernel.org/tip/ca4984a7dd863f3e1c0df775ae3e744bff24c303
Author:        Quentin Perret <qperret@google.com>
AuthorDate:    Thu, 05 Aug 2021 11:21:53 +01:00
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Fri, 06 Aug 2021 14:25:25 +02:00

sched: Fix UCLAMP_FLAG_IDLE setting

The UCLAMP_FLAG_IDLE flag is set on a runqueue when dequeueing the last
uclamp active task (that is, when buckets.tasks reaches 0 for all
buckets) to maintain the last uclamp.max and prevent blocked util from
suddenly becoming visible.

However, there is an asymmetry in how the flag is set and cleared which
can lead to having the flag set whilst there are active tasks on the rq.
Specifically, the flag is cleared in the uclamp_rq_inc() path, which is
called at enqueue time, but set in uclamp_rq_dec_id() which is called
both when dequeueing a task _and_ in the update_uclamp_active() path. As
a result, when both uclamp_rq_{dec,ind}_id() are called from
update_uclamp_active(), the flag ends up being set but not cleared,
hence leaving the runqueue in a broken state.

Fix this by clearing the flag in update_uclamp_active() as well.

Fixes: e496187da710 ("sched/uclamp: Enforce last task's UCLAMP_MAX")
Reported-by: Rick Yiu <rickyiu@google.com>
Signed-off-by: Quentin Perret <qperret@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Qais Yousef <qais.yousef@arm.com>
Tested-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Link: https://lore.kernel.org/r/20210805102154.590709-2-qperret@google.com
---
 kernel/sched/core.c | 25 +++++++++++++++++++------
 1 file changed, 19 insertions(+), 6 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 314f70d..df0480a 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1621,6 +1621,23 @@ static inline void uclamp_rq_dec(struct rq *rq, struct task_struct *p)
 		uclamp_rq_dec_id(rq, p, clamp_id);
 }
 
+static inline void uclamp_rq_reinc_id(struct rq *rq, struct task_struct *p,
+				      enum uclamp_id clamp_id)
+{
+	if (!p->uclamp[clamp_id].active)
+		return;
+
+	uclamp_rq_dec_id(rq, p, clamp_id);
+	uclamp_rq_inc_id(rq, p, clamp_id);
+
+	/*
+	 * Make sure to clear the idle flag if we've transiently reached 0
+	 * active tasks on rq.
+	 */
+	if (clamp_id == UCLAMP_MAX && (rq->uclamp_flags & UCLAMP_FLAG_IDLE))
+		rq->uclamp_flags &= ~UCLAMP_FLAG_IDLE;
+}
+
 static inline void
 uclamp_update_active(struct task_struct *p)
 {
@@ -1644,12 +1661,8 @@ uclamp_update_active(struct task_struct *p)
 	 * affecting a valid clamp bucket, the next time it's enqueued,
 	 * it will already see the updated clamp bucket value.
 	 */
-	for_each_clamp_id(clamp_id) {
-		if (p->uclamp[clamp_id].active) {
-			uclamp_rq_dec_id(rq, p, clamp_id);
-			uclamp_rq_inc_id(rq, p, clamp_id);
-		}
-	}
+	for_each_clamp_id(clamp_id)
+		uclamp_rq_reinc_id(rq, p, clamp_id);
 
 	task_rq_unlock(rq, p, &rf);
 }

  reply	other threads:[~2021-08-06 12:58 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-05 10:21 [PATCH v5 0/2] A couple of uclamp fixes Quentin Perret
2021-08-05 10:21 ` [PATCH v5 1/2] sched: Fix UCLAMP_FLAG_IDLE setting Quentin Perret
2021-08-06 12:57   ` tip-bot2 for Quentin Perret [this message]
2021-08-05 10:21 ` [PATCH v5 2/2] sched: Skip priority checks with SCHED_FLAG_KEEP_PARAMS Quentin Perret
2021-08-06 12:57   ` [tip: sched/core] " tip-bot2 for Quentin Perret

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=162825467066.395.3955621672709689514.tip-bot2@tip-bot2 \
    --to=tip-bot2@linutronix.de \
    --cc=dietmar.eggemann@arm.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-tip-commits@vger.kernel.org \
    --cc=peterz@infradead.org \
    --cc=qais.yousef@arm.com \
    --cc=qperret@google.com \
    --cc=rickyiu@google.com \
    --cc=x86@kernel.org \
    --subject='Re: [tip: sched/core] sched: Fix UCLAMP_FLAG_IDLE setting' \
    /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

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).