From: Thomas Gleixner <tglx@linutronix.de>
To: LKML <linux-kernel@vger.kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Ingo Molnar <mingo@kernel.org>, Will Deacon <will@kernel.org>,
"Paul E . McKenney" <paulmck@kernel.org>,
Joel Fernandes <joel@joelfernandes.org>,
Steven Rostedt <rostedt@goodmis.org>,
Randy Dunlap <rdunlap@infradead.org>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
Logan Gunthorpe <logang@deltatee.com>,
Kurt Schwemmer <kurt.schwemmer@microsemi.com>,
Bjorn Helgaas <bhelgaas@google.com>,
linux-pci@vger.kernel.org, Felipe Balbi <balbi@kernel.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
linux-usb@vger.kernel.org, Kalle Valo <kvalo@codeaurora.org>,
"David S. Miller" <davem@davemloft.net>,
linux-wireless@vger.kernel.org, netdev@vger.kernel.org,
Oleg Nesterov <oleg@redhat.com>,
Davidlohr Bueso <dave@stgolabs.net>,
Michael Ellerman <mpe@ellerman.id.au>,
Arnd Bergmann <arnd@arndb.de>,
linuxppc-dev@lists.ozlabs.org
Subject: [patch V2 09/15] timekeeping: Split jiffies seqlock
Date: Wed, 18 Mar 2020 21:43:11 +0100 [thread overview]
Message-ID: <20200318204408.319891308@linutronix.de> (raw)
In-Reply-To: 20200318204302.693307984@linutronix.de
From: Thomas Gleixner <tglx@linutronix.de>
seqlock consists of a sequence counter and a spinlock_t which is used to
serialize the writers. spinlock_t is substituted by a "sleeping" spinlock
on PREEMPT_RT enabled kernels which breaks the usage in the timekeeping
code as the writers are executed in hard interrupt and therefore
non-preemptible context even on PREEMPT_RT.
The spinlock in seqlock cannot be unconditionally replaced by a
raw_spinlock_t as many seqlock users have nesting spinlock sections or
other code which is not suitable to run in truly atomic context on RT.
Instead of providing a raw_seqlock API for a single use case, open code the
seqlock for the jiffies use case and implement it with a raw_spinlock_t and
a sequence counter.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
kernel/time/jiffies.c | 7 ++++---
kernel/time/tick-common.c | 10 ++++++----
kernel/time/tick-sched.c | 19 ++++++++++++-------
kernel/time/timekeeping.c | 6 ++++--
kernel/time/timekeeping.h | 3 ++-
5 files changed, 28 insertions(+), 17 deletions(-)
--- a/kernel/time/jiffies.c
+++ b/kernel/time/jiffies.c
@@ -58,7 +58,8 @@ static struct clocksource clocksource_ji
.max_cycles = 10,
};
-__cacheline_aligned_in_smp DEFINE_SEQLOCK(jiffies_lock);
+__cacheline_aligned_in_smp DEFINE_RAW_SPINLOCK(jiffies_lock);
+__cacheline_aligned_in_smp seqcount_t jiffies_seq;
#if (BITS_PER_LONG < 64)
u64 get_jiffies_64(void)
@@ -67,9 +68,9 @@ u64 get_jiffies_64(void)
u64 ret;
do {
- seq = read_seqbegin(&jiffies_lock);
+ seq = read_seqcount_begin(&jiffies_seq);
ret = jiffies_64;
- } while (read_seqretry(&jiffies_lock, seq));
+ } while (read_seqcount_retry(&jiffies_seq, seq));
return ret;
}
EXPORT_SYMBOL(get_jiffies_64);
--- a/kernel/time/tick-common.c
+++ b/kernel/time/tick-common.c
@@ -84,13 +84,15 @@ int tick_is_oneshot_available(void)
static void tick_periodic(int cpu)
{
if (tick_do_timer_cpu == cpu) {
- write_seqlock(&jiffies_lock);
+ raw_spin_lock(&jiffies_lock);
+ write_seqcount_begin(&jiffies_seq);
/* Keep track of the next tick event */
tick_next_period = ktime_add(tick_next_period, tick_period);
do_timer(1);
- write_sequnlock(&jiffies_lock);
+ write_seqcount_end(&jiffies_seq);
+ raw_spin_unlock(&jiffies_lock);
update_wall_time();
}
@@ -162,9 +164,9 @@ void tick_setup_periodic(struct clock_ev
ktime_t next;
do {
- seq = read_seqbegin(&jiffies_lock);
+ seq = read_seqcount_begin(&jiffies_seq);
next = tick_next_period;
- } while (read_seqretry(&jiffies_lock, seq));
+ } while (read_seqcount_retry(&jiffies_seq, seq));
clockevents_switch_state(dev, CLOCK_EVT_STATE_ONESHOT);
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -65,7 +65,8 @@ static void tick_do_update_jiffies64(kti
return;
/* Reevaluate with jiffies_lock held */
- write_seqlock(&jiffies_lock);
+ raw_spin_lock(&jiffies_lock);
+ write_seqcount_begin(&jiffies_seq);
delta = ktime_sub(now, last_jiffies_update);
if (delta >= tick_period) {
@@ -91,10 +92,12 @@ static void tick_do_update_jiffies64(kti
/* Keep the tick_next_period variable up to date */
tick_next_period = ktime_add(last_jiffies_update, tick_period);
} else {
- write_sequnlock(&jiffies_lock);
+ write_seqcount_end(&jiffies_seq);
+ raw_spin_unlock(&jiffies_lock);
return;
}
- write_sequnlock(&jiffies_lock);
+ write_seqcount_end(&jiffies_seq);
+ raw_spin_unlock(&jiffies_lock);
update_wall_time();
}
@@ -105,12 +108,14 @@ static ktime_t tick_init_jiffy_update(vo
{
ktime_t period;
- write_seqlock(&jiffies_lock);
+ raw_spin_lock(&jiffies_lock);
+ write_seqcount_begin(&jiffies_seq);
/* Did we start the jiffies update yet ? */
if (last_jiffies_update == 0)
last_jiffies_update = tick_next_period;
period = last_jiffies_update;
- write_sequnlock(&jiffies_lock);
+ write_seqcount_end(&jiffies_seq);
+ raw_spin_unlock(&jiffies_lock);
return period;
}
@@ -676,10 +681,10 @@ static ktime_t tick_nohz_next_event(stru
/* Read jiffies and the time when jiffies were updated last */
do {
- seq = read_seqbegin(&jiffies_lock);
+ seq = read_seqcount_begin(&jiffies_seq);
basemono = last_jiffies_update;
basejiff = jiffies;
- } while (read_seqretry(&jiffies_lock, seq));
+ } while (read_seqcount_retry(&jiffies_seq, seq));
ts->last_jiffies = basejiff;
ts->timer_expires_base = basemono;
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -2397,8 +2397,10 @@ EXPORT_SYMBOL(hardpps);
*/
void xtime_update(unsigned long ticks)
{
- write_seqlock(&jiffies_lock);
+ raw_spin_lock(&jiffies_lock);
+ write_seqcount_begin(&jiffies_seq);
do_timer(ticks);
- write_sequnlock(&jiffies_lock);
+ write_seqcount_end(&jiffies_seq);
+ raw_spin_unlock(&jiffies_lock);
update_wall_time();
}
--- a/kernel/time/timekeeping.h
+++ b/kernel/time/timekeeping.h
@@ -25,7 +25,8 @@ static inline void sched_clock_resume(vo
extern void do_timer(unsigned long ticks);
extern void update_wall_time(void);
-extern seqlock_t jiffies_lock;
+extern raw_spinlock_t jiffies_lock;
+extern seqcount_t jiffies_seq;
#define CS_NAME_LEN 32
next prev parent reply other threads:[~2020-03-18 20:47 UTC|newest]
Thread overview: 72+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-18 20:43 [patch V2 00/15] Lock ordering documentation and annotation for lockdep Thomas Gleixner
2020-03-18 20:43 ` [patch V2 01/15] PCI/switchtec: Fix init_completion race condition with poll_wait() Thomas Gleixner
2020-03-18 21:25 ` Bjorn Helgaas
2020-03-18 20:43 ` [patch V2 02/15] pci/switchtec: Replace completion wait queue usage for poll Thomas Gleixner
2020-03-18 21:26 ` Bjorn Helgaas
2020-03-18 22:11 ` Logan Gunthorpe
2020-03-18 20:43 ` [patch V2 03/15] usb: gadget: Use completion interface instead of open coding it Thomas Gleixner
2020-03-19 8:41 ` Greg Kroah-Hartman
2020-03-18 20:43 ` [patch V2 04/15] orinoco_usb: Use the regular completion interfaces Thomas Gleixner
2020-03-19 8:40 ` Greg Kroah-Hartman
2020-03-18 20:43 ` [patch V2 05/15] acpi: Remove header dependency Thomas Gleixner
2020-03-18 20:43 ` [patch V2 06/15] rcuwait: Add @state argument to rcuwait_wait_event() Thomas Gleixner
2020-03-20 5:36 ` Davidlohr Bueso
2020-03-20 8:45 ` Sebastian Andrzej Siewior
2020-03-20 8:58 ` Davidlohr Bueso
2020-03-20 9:48 ` [PATCH 0/5] Remove mm.h from arch/*/include/asm/uaccess.h Sebastian Andrzej Siewior
2020-03-20 9:48 ` [PATCH 1/5] nds32: Remove mm.h from asm/uaccess.h Sebastian Andrzej Siewior
2020-03-20 9:48 ` [PATCH 2/5] csky: " Sebastian Andrzej Siewior
2020-03-21 11:24 ` Guo Ren
2020-03-21 12:08 ` Thomas Gleixner
2020-03-21 14:11 ` Guo Ren
2020-03-20 9:48 ` [PATCH 3/5] hexagon: " Sebastian Andrzej Siewior
2020-03-20 9:48 ` [PATCH 4/5] ia64: " Sebastian Andrzej Siewior
2020-03-20 9:48 ` [PATCH 5/5] microblaze: " Sebastian Andrzej Siewior
2020-03-18 20:43 ` [patch V2 07/15] powerpc/ps3: Convert half completion to rcuwait Thomas Gleixner
2020-03-19 9:00 ` Sebastian Andrzej Siewior
2020-03-19 9:18 ` Peter Zijlstra
2020-03-19 9:21 ` Davidlohr Bueso
2020-03-19 10:04 ` Christoph Hellwig
2020-03-19 10:26 ` Sebastian Andrzej Siewior
2020-03-20 0:01 ` Geoff Levand
2020-03-20 0:45 ` Michael Ellerman
2020-03-21 10:41 ` Thomas Gleixner
2020-03-18 20:43 ` [patch V2 08/15] Documentation: Add lock ordering and nesting documentation Thomas Gleixner
2020-03-18 22:31 ` Paul E. McKenney
2020-03-19 18:02 ` Thomas Gleixner
2020-03-20 16:01 ` Paul E. McKenney
2020-03-20 19:51 ` Thomas Gleixner
2020-03-20 21:02 ` Paul E. McKenney
2020-03-20 22:36 ` Thomas Gleixner
2020-03-21 2:29 ` Paul E. McKenney
2020-03-21 10:26 ` Thomas Gleixner
2020-03-21 17:23 ` Paul E. McKenney
2020-03-19 8:51 ` Davidlohr Bueso
2020-03-19 15:04 ` Jonathan Corbet
2020-03-19 18:04 ` Thomas Gleixner
2020-03-21 21:21 ` Joel Fernandes
2020-03-21 21:49 ` Thomas Gleixner
2020-03-22 1:36 ` Joel Fernandes
2020-03-18 20:43 ` Thomas Gleixner [this message]
2020-03-18 20:43 ` [patch V2 10/15] sched/swait: Prepare usage in completions Thomas Gleixner
2020-03-18 20:43 ` [patch V2 11/15] completion: Use simple wait queues Thomas Gleixner
2020-03-18 22:28 ` Logan Gunthorpe
2020-03-19 0:33 ` Joel Fernandes
2020-03-19 0:44 ` Thomas Gleixner
2020-03-19 8:42 ` Greg Kroah-Hartman
2020-03-19 17:12 ` Linus Torvalds
2020-03-19 23:25 ` Julian Calaby
2020-03-20 6:59 ` Christoph Hellwig
2020-03-20 9:01 ` Davidlohr Bueso
2020-03-20 8:50 ` [patch V2 00/15] Lock ordering documentation and annotation for lockdep Davidlohr Bueso
2020-03-20 8:55 ` [PATCH 16/15] rcuwait: Get rid of stale name comment Davidlohr Bueso
2020-03-20 8:55 ` [PATCH 17/15] rcuwait: Inform rcuwait_wake_up() users if a wakeup was attempted Davidlohr Bueso
2020-03-20 9:13 ` Sebastian Andrzej Siewior
2020-03-20 10:44 ` Peter Zijlstra
2020-03-20 8:55 ` [PATCH 18/15] kvm: Replace vcpu->swait with rcuwait Davidlohr Bueso
2020-03-20 11:20 ` Paolo Bonzini
2020-03-20 12:54 ` Peter Zijlstra
2020-03-22 16:33 ` Davidlohr Bueso
2020-03-22 22:32 ` Peter Zijlstra
2020-03-20 8:55 ` [PATCH 19/15] sched/swait: Reword some of the main description Davidlohr Bueso
2020-03-20 9:19 ` Sebastian Andrzej Siewior
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