Use the local_irq_*_nort variants to reduce latencies in RT. The code
is serialized by the locks. No need to disable interrupts.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Fixes in_atomic stack-dump, when Mellanox module is loaded into the RT
Kernel.
Michael S. Tsirkin <mst@dev.mellanox.co.il> sayeth:
"Basically, if you just make spin_lock_irqsave (and spin_lock_irq) not disable
interrupts for non-raw spinlocks, I think all of infiniband will be fine without
changes."
Signed-off-by: Sven-Thorsten Dietrich <sven@thebigcorporation.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Use the local_irq_*_nort variants.
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
RT needs a few preempt_disable/enable points which are not necessary
otherwise. Implement variants to avoid #ifdeffery.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Add local_irq_*_(no)rt variant which are mainly used to break
interrupt disabled sections on PREEMPT_RT or to explicitely disable
interrupts on PREEMPT_RT.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
If the user specified a threshold at module load time, use it.
Cc: stable-rt@vger.kernel.org
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Mike Galbraith <bitbucket@online.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
There's no reason to use stop machine to search for hardware latency.
Simply disabling interrupts while running the loop will do enough to
check if something comes in that wasn't disabled by interrupts being
off, which is exactly what stop machine does.
Instead of using stop machine, just have the thread disable interrupts
while it checks for hardware latency.
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
As ktime_get() calls into the timing code which does a read_seq(), it
may be affected by other CPUS that touch that lock. To remove this
dependency, use the trace_clock_local() which is already exported
for module use. If CONFIG_TRACING is enabled, use that as the clock,
otherwise use ktime_get().
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
The hwlat_detector reads two timestamps in a row, then reports any
gap between those calls. The problem is, it misses everything between
the second reading of the time stamp to the first reading of the time stamp
in the next loop. That's were most of the time is spent, which means,
chances are likely that it will miss all hardware latencies. This
defeats the purpose.
By also testing the first time stamp from the previous loop second
time stamp (the outer loop), we are more likely to find a latency.
Setting the threshold to 1, here's what the report now looks like:
1347415723.0232202770 0 2
1347415725.0234202822 0 2
1347415727.0236202875 0 2
1347415729.0238202928 0 2
1347415731.0240202980 0 2
1347415734.0243203061 0 2
1347415736.0245203113 0 2
1347415738.0247203166 2 0
1347415740.0249203219 0 3
1347415742.0251203272 0 3
1347415743.0252203299 0 3
1347415745.0254203351 0 2
1347415747.0256203404 0 2
1347415749.0258203457 0 2
1347415751.0260203510 0 2
1347415754.0263203589 0 2
1347415756.0265203642 0 2
1347415758.0267203695 0 2
1347415760.0269203748 0 2
1347415762.0271203801 0 2
1347415764.0273203853 2 0
There's some hardware latency that takes 2 microseconds to run.
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Jon Masters developed this wonderful SMI detector. For details please
consult Documentation/hwlat_detector.txt. It could be ported to Linux
3.0 RT without any major change.
Signed-off-by: Carsten Emde <C.Emde@osadl.org>
This patch provides a recording mechanism to store data of potential
sources of system latencies. The recordings separately determine the
latency caused by a delayed timer expiration, by a delayed wakeup of the
related user space program and by the sum of both. The histograms can be
enabled and reset individually. The data are accessible via the debug
filesystem. For details please consult Documentation/trace/histograms.txt.
Signed-off-by: Carsten Emde <C.Emde@osadl.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
The waitqueue is protected by the pci_lock, so we can just avoid to
lock the waitqueue lock itself. That prevents the
might_sleep()/scheduling while atomic problem on RT
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable-rt@vger.kernel.org
Preemption must be disabled before enabling interrupts in do_trap
on x86_64 because the stack in use for int3 and debug is a per CPU
stack set by th IST. But 32bit does not have an IST and the stack
still belongs to the current task and there is no problem in scheduling
out the task.
Keep preemption enabled on X86_32 when enabling interrupts for
do_trap().
The name of the function is changed from preempt_conditional_sti/cli()
to conditional_sti/cli_ist(), to annotate that this function is used
when the stack is on the IST.
Cc: stable-rt@vger.kernel.org
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
With threaded interrupts we might see an interrupt in progress on
migration. Do not unmask it when this is the case.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
On PREEMPT_RT enabled systems the interrupt handler run as threads at prio 50
(by default). If a high priority userspace process tries to shut down a busy
network interface it might spin in a yield loop waiting for the device to
become idle. With the interrupt thread having a lower priority than the
looping process it might never be scheduled and so result in a deadlock on UP
systems.
With Magic SysRq the following backtrace can be produced:
> test_app R running 0 174 168 0x00000000
> [<c02c7070>] (__schedule+0x220/0x3fc) from [<c02c7870>] (preempt_schedule_irq+0x48/0x80)
> [<c02c7870>] (preempt_schedule_irq+0x48/0x80) from [<c0008fa8>] (svc_preempt+0x8/0x20)
> [<c0008fa8>] (svc_preempt+0x8/0x20) from [<c001a984>] (local_bh_enable+0x18/0x88)
> [<c001a984>] (local_bh_enable+0x18/0x88) from [<c025316c>] (dev_deactivate_many+0x220/0x264)
> [<c025316c>] (dev_deactivate_many+0x220/0x264) from [<c023be04>] (__dev_close_many+0x64/0xd4)
> [<c023be04>] (__dev_close_many+0x64/0xd4) from [<c023be9c>] (__dev_close+0x28/0x3c)
> [<c023be9c>] (__dev_close+0x28/0x3c) from [<c023f7f0>] (__dev_change_flags+0x88/0x130)
> [<c023f7f0>] (__dev_change_flags+0x88/0x130) from [<c023f904>] (dev_change_flags+0x10/0x48)
> [<c023f904>] (dev_change_flags+0x10/0x48) from [<c024c140>] (do_setlink+0x370/0x7ec)
> [<c024c140>] (do_setlink+0x370/0x7ec) from [<c024d2f0>] (rtnl_newlink+0x2b4/0x450)
> [<c024d2f0>] (rtnl_newlink+0x2b4/0x450) from [<c024cfa0>] (rtnetlink_rcv_msg+0x158/0x1f4)
> [<c024cfa0>] (rtnetlink_rcv_msg+0x158/0x1f4) from [<c0256740>] (netlink_rcv_skb+0xac/0xc0)
> [<c0256740>] (netlink_rcv_skb+0xac/0xc0) from [<c024bbd8>] (rtnetlink_rcv+0x18/0x24)
> [<c024bbd8>] (rtnetlink_rcv+0x18/0x24) from [<c02561b8>] (netlink_unicast+0x13c/0x198)
> [<c02561b8>] (netlink_unicast+0x13c/0x198) from [<c025651c>] (netlink_sendmsg+0x264/0x2e0)
> [<c025651c>] (netlink_sendmsg+0x264/0x2e0) from [<c022af98>] (sock_sendmsg+0x78/0x98)
> [<c022af98>] (sock_sendmsg+0x78/0x98) from [<c022bb50>] (___sys_sendmsg.part.25+0x268/0x278)
> [<c022bb50>] (___sys_sendmsg.part.25+0x268/0x278) from [<c022cf08>] (__sys_sendmsg+0x48/0x78)
> [<c022cf08>] (__sys_sendmsg+0x48/0x78) from [<c0009320>] (ret_fast_syscall+0x0/0x2c)
This patch works around the problem by replacing yield() by msleep(1), giving
the interrupt thread time to finish, similar to other changes contained in the
rt patch set. Using wait_for_completion() instead would probably be a better
solution.
Cc: stable-rt@vger.kernel.org
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
timekeeping suspend/resume calls read_persistant_clock() which takes
rtc_lock. That results in might sleep warnings because at that point
we run with interrupts disabled.
We cannot convert rtc_lock to a raw spinlock as that would trigger
other might sleep warnings.
As a temporary workaround we disable the might sleep warnings by
setting system_state to SYSTEM_SUSPEND before calling sysdev_suspend()
and restoring it to SYSTEM_RUNNING afer sysdev_resume().
Needs to be revisited.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Add a pagefault_disabled variable to task_struct to allow decoupling
the pagefault-disabled logic from the preempt count.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Use disable_irq_nosync() instead of disable_irq() as this might be
called in atomic context with netpoll.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
As default the TCLIB uses the 32KiHz base clock rate for clock events.
Add a compile time selection to allow higher clock resulution.
(fixed up by Sami Pietikäinen <Sami.Pietikainen@wapice.com>)
Signed-off-by: Benedikt Spranger <b.spranger@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Setup and remove the interrupt handler in clock event mode selection.
This avoids calling the (shared) interrupt handler when the device is
not used.
Signed-off-by: Benedikt Spranger <b.spranger@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
[bigeasy: redo the patch with NR_IRQS_LEGACY which is probably required since
commit 8fe82a55 ("ARM: at91: sparse irq support") which is included since v3.6.
Patch based on what Sami Pietikäinen <Sami.Pietikainen@wapice.com> suggested].
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
No need to keep preemption disabled across the whole function.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
On x86_64 we must disable preemption before we enable interrupts
for stack faults, int3 and debugging, because the current task is using
a per CPU debug stack defined by the IST. If we schedule out, another task
can come in and use the same stack and cause the stack to be corrupted
and crash the kernel on return.
When CONFIG_PREEMPT_RT_FULL is enabled, spin_locks become mutexes, and
one of these is the spin lock used in signal handling.
Some of the debug code (int3) causes do_trap() to send a signal.
This function calls a spin lock that has been converted to a mutex
and has the possibility to sleep. If this happens, the above issues with
the corrupted stack is possible.
Instead of calling the signal right away, for PREEMPT_RT and x86_64,
the signal information is stored on the stacks task_struct and
TIF_NOTIFY_RESUME is set. Then on exit of the trap, the signal resume
code will send the signal when preemption is enabled.
[ rostedt: Switched from #ifdef CONFIG_PREEMPT_RT_FULL to
ARCH_RT_DELAYS_SIGNAL_SEND and added comments to the code. ]
Cc: stable-rt@vger.kernel.org
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
The arm boot_lock is used by the secondary processor startup code. The locking
task is the idle thread, which has idle->sched_class == &idle_sched_class.
idle_sched_class->enqueue_task == NULL, so if the idle task blocks on the
lock, the attempt to wake it when the lock becomes available will fail:
try_to_wake_up()
...
activate_task()
enqueue_task()
p->sched_class->enqueue_task(rq, p, flags)
Fix by converting boot_lock to a raw spin lock.
Signed-off-by: Frank Rowand <frank.rowand@am.sony.com>
Link: http://lkml.kernel.org/r/4E77B952.3010606@am.sony.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
As explained by Alexander Fyodorov <halcy@yandex.ru>:
|read_lock(&tasklist_lock) in ptrace_stop() is converted to mutex on RT kernel,
|and it can remove __TASK_TRACED from task->state (by moving it to
|task->saved_state). If parent does wait() on child followed by a sys_ptrace
|call, the following race can happen:
|
|- child sets __TASK_TRACED in ptrace_stop()
|- parent does wait() which eventually calls wait_task_stopped() and returns
| child's pid
|- child blocks on read_lock(&tasklist_lock) in ptrace_stop() and moves
| __TASK_TRACED flag to saved_state
|- parent calls sys_ptrace, which calls ptrace_check_attach() and wait_task_inactive()
The patch is based on his initial patch where an additional check is
added in case the __TASK_TRACED moved to ->saved_state. The pi_lock is
taken in case the caller is interrupted between looking into ->state and
->saved_state.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
The preempt_schedule() uses the preempt_disable_notrace() version
because it can cause infinite recursion by the function tracer as
the function tracer uses preempt_enable_notrace() which may call
back into the preempt_schedule() code as the NEED_RESCHED is still
set and the PREEMPT_ACTIVE has not been set yet.
See commit: d1f74e20b5 that made this
change.
The preemptoff and preemptirqsoff latency tracers require the first
and last preempt count modifiers to enable tracing. But this skips
the checks. Since we can not convert them back to the non notrace
version, we can use the idle() hooks for the latency tracers here.
That is, the start/stop_critical_timings() works well to manually
start and stop the latency tracer for preempt off timings.
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Clark Williams <williams@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Moving the blk_sched_flush_plug() call out of the interrupt/preempt
disabled region in the scheduler allows us to replace
local_irq_save/restore(flags) by local_irq_disable/enable() in
blk_flush_plug().
Now instead of doing this we disable interrupts explicitely when we
lock the request_queue and reenable them when we drop the lock. That
allows interrupts to be handled when the plug list contains requests
for more than one queue.
Aside of that this change makes the scope of the irq disabled region
more obvious. The current code confused the hell out of me when
looking at:
local_irq_save(flags);
spin_lock(q->queue_lock);
...
queue_unplugged(q...);
scsi_request_fn();
spin_unlock(q->queue_lock);
spin_lock(shost->host_lock);
spin_unlock_irq(shost->host_lock);
-------------------^^^ ????
spin_lock_irq(q->queue_lock);
spin_unlock(q->lock);
local_irq_restore(flags);
Also add a comment to __blk_run_queue() documenting that
q->request_fn() can drop q->queue_lock and reenable interrupts, but
must return with q->queue_lock held and interrupts disabled.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/20110622174919.025446432@linutronix.de
Thomas Gleixner
Ingo Molnar
Sven-Thorsten Dietrich
Steven Rostedt
Peter Zijlstra
Mike Galbraith
Steven Rostedt
Carsten Emde
Marc Kleine-Budde
Peter Zijlstra
Benedikt Spranger
Oleg Nesterov
Frank Rowand
Sebastian Andrzej Siewior