linux-kernel - [tip: timers/core] timers: Do not IPI for deferrable timers

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <170308794956.398.15756777803011185741.tip-bot2@tip-bot2>
Date: Wed, 20 Dec 2023 15:59:09 -0000
From: "tip-bot2 for Anna-Maria Behnsen" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: "Anna-Maria Behnsen" <anna-maria@...utronix.de>,
 Thomas Gleixner <tglx@...utronix.de>,
 Frederic Weisbecker <frederic@...nel.org>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject: [tip: timers/core] timers: Do not IPI for deferrable timers

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

Commit-ID:     d124c3393e798b1fb142ee728d5c8976d11e722d
Gitweb:        https://git.kernel.org/tip/d124c3393e798b1fb142ee728d5c8976d11e722d
Author:        Anna-Maria Behnsen <anna-maria@...utronix.de>
AuthorDate:    Fri, 01 Dec 2023 10:26:28 +01:00
Committer:     Thomas Gleixner <tglx@...utronix.de>
CommitterDate: Wed, 20 Dec 2023 16:49:38 +01:00

timers: Do not IPI for deferrable timers

Deferrable timers do not prevent CPU from going idle and are not taken into
account on idle path. Sending an IPI to a remote CPU when a new first
deferrable timer was enqueued will wake up the remote CPU but nothing will
be done regarding the deferrable timers.

Drop IPI completely when a new first deferrable timer was enqueued.

Signed-off-by: Anna-Maria Behnsen <anna-maria@...utronix.de>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Reviewed-by: Frederic Weisbecker <frederic@...nel.org>
Link: https://lore.kernel.org/r/20231201092654.34614-7-anna-maria@linutronix.de

---
 kernel/time/timer.c | 15 ++++++---------
 1 file changed, 6 insertions(+), 9 deletions(-)

diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index ed8d606..9188205 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -571,18 +571,15 @@ static int calc_wheel_index(unsigned long expires, unsigned long clk,
 static void
 trigger_dyntick_cpu(struct timer_base *base, struct timer_list *timer)
 {
-	if (!is_timers_nohz_active())
-		return;
-
 	/*
-	 * TODO: This wants some optimizing similar to the code below, but we
-	 * will do that when we switch from push to pull for deferrable timers.
+	 * Deferrable timers do not prevent the CPU from entering dynticks and
+	 * are not taken into account on the idle/nohz_full path. An IPI when a
+	 * new deferrable timer is enqueued will wake up the remote CPU but
+	 * nothing will be done with the deferrable timer base. Therefore skip
+	 * the remote IPI for deferrable timers completely.
 	 */
-	if (timer->flags & TIMER_DEFERRABLE) {
-		if (tick_nohz_full_cpu(base->cpu))
-			wake_up_nohz_cpu(base->cpu);
+	if (!is_timers_nohz_active() || timer->flags & TIMER_DEFERRABLE)
 		return;
-	}
 
 	/*
 	 * We might have to IPI the remote CPU if the base is idle and the