this warning:
kernel/hrtimer.c: In function ‘hrtimer_cpu_notify’:
kernel/hrtimer.c:1574: warning: unused variable ‘dcpu’
is caused because 'dcpu' is only used in the CONFIG_HOTPLUG_CPU case.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
> Ingo, this addition fixes the hotplug issue on my machine
And because we're all human...
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: fix hrtimer locking (reported by lockdep) in the CPU hotplug case
This addition fixes the hotplug locking issue on my machine
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: cleanup, move all hrtimer processing into hardirq context
This is an attempt at removing some of the hrtimer complexity by
reducing the number of callback modes to 1.
This means that all hrtimer callback functions will be ran from HARD-irq
context.
I went through all the 30 odd hrtimer callback functions in the kernel
and saw only one that I'm not quite sure of, which is the one in
net/can/bcm.c - hence I'm CC-ing the folks responsible for that code.
Furthermore, the hrtimer core now calls callbacks directly with IRQs
disabled in case you try to enqueue an expired timer. If this timer is a
periodic timer (which should use hrtimer_forward() to advance its time)
then it might be possible to end up in an inf. recursive loop due to the
fact that hrtimer_forward() doesn't round up to the next timer
granularity, and therefore keeps on calling the callback - obviously
this needs a fix.
Aside from that, this seems to compile and actually boot on my dual core
test box - although I'm sure there are some bugs in, me not hitting any
makes me certain :-)
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: fix incorrect locking triggered during hotplug-intense stress-tests
While migrating the the CB_IRQSAFE_UNLOCKED timers during a cpu-offline,
we queue them on the cb_pending list, so that they won't go
stale.
Thus, when the callbacks of the timers run from the softirq context,
they could run into potential deadlocks, since these callbacks
assume that they're running with irq's disabled, thereby annoying
lockdep!
Fix this by emulating hardirq context while running these callbacks from
the hrtimer softirq.
=================================
[ INFO: inconsistent lock state ]
2.6.27 #2
--------------------------------
inconsistent {in-hardirq-W} -> {hardirq-on-W} usage.
ksoftirqd/0/4 [HC0[0]:SC1[1]:HE1:SE0] takes:
(&rq->lock){++..}, at: [<c011db84>] sched_rt_period_timer+0x9e/0x1fc
{in-hardirq-W} state was registered at:
[<c014103c>] __lock_acquire+0x549/0x121e
[<c0107890>] native_sched_clock+0x88/0x99
[<c013aa12>] clocksource_get_next+0x39/0x3f
[<c0139abc>] update_wall_time+0x616/0x7df
[<c0141d6b>] lock_acquire+0x5a/0x74
[<c0121724>] scheduler_tick+0x3a/0x18d
[<c047ed45>] _spin_lock+0x1c/0x45
[<c0121724>] scheduler_tick+0x3a/0x18d
[<c0121724>] scheduler_tick+0x3a/0x18d
[<c012c436>] update_process_times+0x3a/0x44
[<c013c044>] tick_periodic+0x63/0x6d
[<c013c062>] tick_handle_periodic+0x14/0x5e
[<c010568c>] timer_interrupt+0x44/0x4a
[<c0150c9f>] handle_IRQ_event+0x13/0x3d
[<c0151c14>] handle_level_irq+0x79/0xbd
[<c0105634>] do_IRQ+0x69/0x7d
[<c01041e4>] common_interrupt+0x28/0x30
[<c047007b>] aac_probe_one+0x1a3/0x3f3
[<c047ec2d>] _spin_unlock_irqrestore+0x36/0x39
[<c01512b4>] setup_irq+0x1be/0x1f9
[<c065d70b>] start_kernel+0x259/0x2c5
[<ffffffff>] 0xffffffff
irq event stamp: 50102
hardirqs last enabled at (50102): [<c047ebf4>] _spin_unlock_irq+0x20/0x23
hardirqs last disabled at (50101): [<c047edc2>] _spin_lock_irq+0xa/0x4b
softirqs last enabled at (50088): [<c0128ba6>] do_softirq+0x37/0x4d
softirqs last disabled at (50099): [<c0128ba6>] do_softirq+0x37/0x4d
other info that might help us debug this:
no locks held by ksoftirqd/0/4.
stack backtrace:
Pid: 4, comm: ksoftirqd/0 Not tainted 2.6.27 #2
[<c013f6cb>] print_usage_bug+0x13e/0x147
[<c013fef5>] mark_lock+0x493/0x797
[<c01410b1>] __lock_acquire+0x5be/0x121e
[<c0141d6b>] lock_acquire+0x5a/0x74
[<c011db84>] sched_rt_period_timer+0x9e/0x1fc
[<c047ed45>] _spin_lock+0x1c/0x45
[<c011db84>] sched_rt_period_timer+0x9e/0x1fc
[<c011db84>] sched_rt_period_timer+0x9e/0x1fc
[<c01210fd>] finish_task_switch+0x41/0xbd
[<c0107890>] native_sched_clock+0x88/0x99
[<c011dae6>] sched_rt_period_timer+0x0/0x1fc
[<c0136dda>] run_hrtimer_pending+0x54/0xe5
[<c011dae6>] sched_rt_period_timer+0x0/0x1fc
[<c0128afb>] __do_softirq+0x7b/0xef
[<c0128ba6>] do_softirq+0x37/0x4d
[<c0128c12>] ksoftirqd+0x56/0xc5
[<c0128bbc>] ksoftirqd+0x0/0xc5
[<c0134649>] kthread+0x38/0x5d
[<c0134611>] kthread+0x0/0x5d
[<c0104477>] kernel_thread_helper+0x7/0x10
=======================
Signed-off-by: Gautham R Shenoy <ego@in.ibm.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
There's a small race/chance that, while hrtimers are enabled globally,
they're later not enabled when we're calling the hrtimer_interrupt() function,
which then BUG_ON()'s for that. This patch closes that race/gap.
Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Impact: per CPU hrtimers can be migrated from a dead CPU
The hrtimer code has no knowledge about per CPU timers, but we need to
prevent the migration of such timers and warn when such a timer is
active at migration time.
Explicitely mark the timers as per CPU and use a more understandable
mode descriptor for the interrupts safe unlocked callback mode, which
is used by hrtimer_sleeper and the scheduler code.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Impact: during migration active hrtimers can be seen as inactive
The migration code removes the hrtimers from the queues of the dead
CPU and sets the state temporary to INACTIVE. The enqueue code sets it
to ACTIVE/PENDING again.
Prevent that the wrong state can be seen by using a separate migration
state bit.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Impact: Stale timers after a CPU went offline.
commit 37bb6cb409
hrtimer: unlock hrtimer_wakeup
changed the hrtimer sleeper callback mode to CB_IRQSAFE_NO_SOFTIRQ due
to locking problems. A result of this change is that when enqueue is
called for an already expired hrtimer the callback function is not
longer called directly from the enqueue code. The normal callers have
been fixed in the code, but the migration code which moves hrtimers
from a dead CPU to a live CPU was not made aware of this.
This can be fixed by checking the timer state after the call to
enqueue in the migration code.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Impact: hrtimers which are on the pending list are not migrated at cpu
offline and can be stale forever
Add the pending list migration when CONFIG_HIGH_RES_TIMERS is enabled
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Peter Zijlstra noticed this 8 months ago and I just noticed
it again.
hrtimer_clock_base::get_softirq_time() is currently unused
in the entire tree. In fact, looking at the logs, it appears
as if it was never used. Remove it.
Signed-off-by: Mark McLoughlin <markmc@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
As part of going idle, we already look at the time of the next timer event to determine
which C-state to select etc.
This patch adds functionality that causes the timers that are past their
soft expire time, to fire at this time, before we calculate the next wakeup
time. This functionality will thus avoid wakeups by running timers before
going idle rather than specially waking up for it.
Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
This patch makes the nanosleep() system call use the per process
slack value; with this users are able to externally control existing
applications to reduce the wakeup rate.
Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
this patch adds a _range version of hrtimer_start() so that range timers
can be created; the hrtimer_start() function is just a wrapper around this.
In addition, hrtimer_start_expires() will now preserve existing ranges.
Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
this patch turns hrtimers into range timers; they have 2 expire points
1) the soft expire point
2) the hard expire point
the kernel will do it's regular best effort attempt to get the timer run
at the hard expire point. However, if some other time fires after the soft
expire point, the kernel now has the freedom to fire this timer at this point,
and thus grouping the events and preventing a power-expensive wakeup in the
future.
Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
In order to be able to do range hrtimers we need to use accessor functions
to the "expire" member of the hrtimer struct.
This patch converts kernel/* to these accessors.
Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
This patch adds a schedule_hrtimeout() function, to be used by select() and
poll() in a later patch. This function works similar to schedule_timeout()
in most ways, but takes a timespec rather than jiffies.
With a lot of contributions/fixes from Thomas
Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Add the comment to explain why the double lock in migrate_timers()
can't deadlock.
Change the code to use spinlock_irq() instead of local_irq_disable()
+ spin_lock().
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Acked-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
