From: "tip-bot2 for Thomas Gleixner" <tip-bot2@linutronix.de>
To: linux-tip-commits@vger.kernel.org
Cc: Thomas Gleixner <tglx@linutronix.de>,
x86@kernel.org, linux-kernel@vger.kernel.org
Subject: [tip: timers/core] tick: Document protections for tick related data
Date: Thu, 19 Nov 2020 09:55:10 -0000 [thread overview]
Message-ID: <160577971028.11244.17384834287904608390.tip-bot2@tip-bot2> (raw)
In-Reply-To: <20201117132006.197713794@linutronix.de>
The following commit has been merged into the timers/core branch of tip:
Commit-ID: c398960cd82b233886fbff163986f998b5a5c008
Gitweb: https://git.kernel.org/tip/c398960cd82b233886fbff163986f998b5a5c008
Author: Thomas Gleixner <tglx@linutronix.de>
AuthorDate: Tue, 17 Nov 2020 14:19:44 +01:00
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Thu, 19 Nov 2020 10:48:28 +01:00
tick: Document protections for tick related data
The protection rules for tick_next_period and last_jiffies_update are blury
at best. Clarify this.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20201117132006.197713794@linutronix.de
---
kernel/time/tick-common.c | 4 +++-
kernel/time/tick-sched.c | 4 +++-
2 files changed, 6 insertions(+), 2 deletions(-)
diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c
index 6c9c342..68504eb 100644
--- a/kernel/time/tick-common.c
+++ b/kernel/time/tick-common.c
@@ -27,7 +27,9 @@
*/
DEFINE_PER_CPU(struct tick_device, tick_cpu_device);
/*
- * Tick next event: keeps track of the tick time
+ * Tick next event: keeps track of the tick time. It's updated by the
+ * CPU which handles the tick and protected by jiffies_lock. There is
+ * no requirement to write hold the jiffies seqcount for it.
*/
ktime_t tick_next_period;
ktime_t tick_period;
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 81632cd..15360e6 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -44,7 +44,9 @@ struct tick_sched *tick_get_tick_sched(int cpu)
#if defined(CONFIG_NO_HZ_COMMON) || defined(CONFIG_HIGH_RES_TIMERS)
/*
- * The time, when the last jiffy update happened. Protected by jiffies_lock.
+ * The time, when the last jiffy update happened. Write access must hold
+ * jiffies_lock and jiffies_seq. tick_nohz_next_event() needs to get a
+ * consistent view of jiffies and last_jiffies_update.
*/
static ktime_t last_jiffies_update;
next prev parent reply other threads:[~2020-11-19 9:55 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-17 13:19 [patch 0/7] tick: Cleanups and reduce jiffies_seq held times Thomas Gleixner
2020-11-17 13:19 ` [patch 1/7] tick/broadcast: Serialize access to tick_next_period Thomas Gleixner
2020-11-19 9:55 ` [tip: timers/core] " tip-bot2 for Thomas Gleixner
2020-11-17 13:19 ` [patch 2/7] tick: Document protections for tick related data Thomas Gleixner
2020-11-19 9:55 ` tip-bot2 for Thomas Gleixner [this message]
2020-11-17 13:19 ` [patch 3/7] tick/sched: Use tick_next_period for lockless quick check Thomas Gleixner
2020-11-19 9:55 ` [tip: timers/core] " tip-bot2 for Thomas Gleixner
2020-11-17 13:19 ` [patch 4/7] tick/sched: Reduce seqcount held scope in tick_do_update_jiffies64() Thomas Gleixner
2020-11-19 9:55 ` [tip: timers/core] " tip-bot2 for Yunfeng Ye
2020-11-17 13:19 ` [patch 5/7] tick/sched: Optimize tick_do_update_jiffies64() further Thomas Gleixner
2020-11-19 9:55 ` [tip: timers/core] " tip-bot2 for Thomas Gleixner
2020-11-17 13:19 ` [patch 6/7] tick/sched: Release seqcount before invoking calc_load_global() Thomas Gleixner
2020-11-19 9:55 ` [tip: timers/core] " tip-bot2 for Yunfeng Ye
2020-11-17 13:19 ` [patch 7/7] tick: Get rid of tick_period Thomas Gleixner
2020-11-19 9:55 ` [tip: timers/core] " tip-bot2 for Thomas Gleixner
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