| Age | Commit message (Collapse) | Author |
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Introduce managed counterparts for alloc_percpu() and free_percpu().
Add devm_alloc_percpu() and devm_free_percpu() into the managed
interfaces list.
Signed-off-by: Madalin Bucur <madalin.bucur@freescale.com>
Change-Id: I93546348e7b0e1974fda8b6c7a3b3710ce45b724
Reviewed-on: http://git.am.freescale.net:8181/24140
Reviewed-by: Madalin-Cristian Bucur <madalin.bucur@freescale.com>
Tested-by: Madalin-Cristian Bucur <madalin.bucur@freescale.com>
Conflicts:
Documentation/driver-model/devres.txt
drivers/base/devres.c
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Signed-off-by: Madalin Bucur <madalin.bucur@freescale.com>
Change-Id: I6a27c4300890d8c3a2f892bbbc254ebc9ce6d538
Reviewed-on: http://git.am.freescale.net:8181/16879
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Support for multiple drivers per kernel module comes in kernel 3.14
so we are forced to generate several modules for the advanced drivers.
This patch can be dropped when the code is rebased on a kernel newer
than 3.14. The problem is with the MODULE_DEVICE_TABLE macro that only
from 3.14 generates different named structured based on the name
parameter. The change that introduces that also needs a synchronized
change in scripts/mod/file2alias.c.
Signed-off-by: Madalin Bucur <madalin.bucur@freescale.com>
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Signed-off-by: Madalin Bucur <madalin.bucur@freescale.com>
Change-Id: I24f7b9c39c1cf24dbb78987c491ab9a56c22eb10
Reviewed-on: http://git.am.freescale.net:8181/15302
Tested-by: Review Code-CDREVIEW <CDREVIEW@freescale.com>
Reviewed-by: Cristian Bercaru <cristian.bercaru@freescale.com>
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Add symbol exports required by the advanced drivers.
Signed-off-by: Madalin Bucur <madalin.bucur@freescale.com>
Change-Id: I66f280f8ec9fb1da73dc2db772c0287360fa5417
Reviewed-on: http://git.am.freescale.net:8181/15300
Tested-by: Review Code-CDREVIEW <CDREVIEW@freescale.com>
Reviewed-by: Cristian Bercaru <cristian.bercaru@freescale.com>
Conflicts:
drivers/net/ethernet/freescale/dpa/dpaa_eth_common.c
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Signed-off-by: Madalin Bucur <madalin.bucur@freescale.com>
Change-Id: I4bb6955baf63962dbb5dda09fd2302dbaba9c85a
Reviewed-on: http://git.am.freescale.net:8181/15299
Tested-by: Review Code-CDREVIEW <CDREVIEW@freescale.com>
Reviewed-by: Cristian Bercaru <cristian.bercaru@freescale.com>
Conflicts:
drivers/net/ethernet/freescale/dpa/Makefile
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Group DPAA Ethernet generic driver code under one Kconfig option.
Signed-off-by: Madalin Bucur <madalin.bucur@freescale.com>
Change-Id: I96061198d022d344280f8b52b14f25e9b3daf2ba
Reviewed-on: http://git.am.freescale.net:8181/15298
Reviewed-by: Cristian Bercaru <cristian.bercaru@freescale.com>
Conflicts:
drivers/net/ethernet/freescale/dpa/Makefile
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Group the DPAA Ethernet advanced drivers under one Kconfig option.
Signed-off-by: Madalin Bucur <madalin.bucur@freescale.com>
Change-Id: I832e0dd99e18087fa0b091373f023c67ea69a434
Reviewed-on: http://git.am.freescale.net:8181/15297
Tested-by: Review Code-CDREVIEW <CDREVIEW@freescale.com>
Reviewed-by: Cristian Bercaru <cristian.bercaru@freescale.com>
Conflicts:
drivers/net/ethernet/freescale/dpa/Kconfig
drivers/net/ethernet/freescale/dpa/Makefile
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Use a common initialization function for MACless, shared and proxy
Ethernet drivers.
Signed-off-by: Madalin Bucur <madalin.bucur@freescale.com>
Change-Id: I7a0ec70b33ad7ad92cb559dbd828572f83b5c98e
Reviewed-on: http://git.am.freescale.net:8181/15296
Tested-by: Review Code-CDREVIEW <CDREVIEW@freescale.com>
Reviewed-by: Cristian Bercaru <cristian.bercaru@freescale.com>
Conflicts:
drivers/net/ethernet/freescale/dpa/dpaa_eth_base.c
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Initialize debugfs from the DPAA generic driver.
Signed-off-by: Madalin Bucur <madalin.bucur@freescale.com>
Change-Id: I032589647a56a6704b4044078a8468ca786149fc
Reviewed-on: http://git.am.freescale.net:8181/15295
Tested-by: Review Code-CDREVIEW <CDREVIEW@freescale.com>
Reviewed-by: Cristian Bercaru <cristian.bercaru@freescale.com>
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Move dpaa_debugfs.h header inclusion where needed.
Signed-off-by: Madalin Bucur <madalin.bucur@freescale.com>
Change-Id: I2d85c4bc3822987d019bde07b7539875872b9125
Reviewed-on: http://git.am.freescale.net:8181/15294
Tested-by: Review Code-CDREVIEW <CDREVIEW@freescale.com>
Reviewed-by: Cristian Bercaru <cristian.bercaru@freescale.com>
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DPAA Ethernet debugfs is initialized from the Ethernet driver.
Signed-off-by: Madalin Bucur <madalin.bucur@freescale.com>
Change-Id: Ia42ee938286cede2e60837388f376b477bc28c62
Reviewed-on: http://git.am.freescale.net:8181/15293
Tested-by: Review Code-CDREVIEW <CDREVIEW@freescale.com>
Reviewed-by: Cristian Bercaru <cristian.bercaru@freescale.com>
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Removed empty code.
Signed-off-by: Madalin Bucur <madalin.bucur@freescale.com>
Change-Id: I0abc82f3a49b073044d5cabd704ff4771990dcfb
Reviewed-on: http://git.am.freescale.net:8181/15292
Tested-by: Review Code-CDREVIEW <CDREVIEW@freescale.com>
Reviewed-by: Cristian Bercaru <cristian.bercaru@freescale.com>
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Tristate option in Kconfig is not supported for those features.
Signed-off-by: Madalin Bucur <madalin.bucur@freescale.com>
Change-Id: I2215749c57b56a5f6bb1b426a819beda97926e81
Reviewed-on: http://git.am.freescale.net:8181/15291
Reviewed-by: Cristian Bercaru <cristian.bercaru@freescale.com>
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Signed-off-by: Madalin Bucur <madalin.bucur@freescale.com>
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Exported API is used by the Ethernet driver.
Signed-off-by: Madalin Bucur <madalin.bucur@freescale.com>
Conflicts:
drivers/net/ethernet/freescale/dpa/mac-api.c
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Signed-off-by: Scott Wood <scottwood@freescale.com>
Conflicts:
arch/arm/kvm/mmu.c
arch/arm/mm/proc-v7-3level.S
arch/powerpc/kernel/vdso32/getcpu.S
drivers/crypto/caam/error.c
drivers/crypto/caam/sg_sw_sec4.h
drivers/usb/host/ehci-fsl.c
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Austin reported a XFS deadlock/stall on RT where scheduled work gets
never exececuted and tasks are waiting for each other for ever.
The underlying problem is the modification of the RT code to the
handling of workers which are about to go to sleep. In mainline a
worker thread which goes to sleep wakes an idle worker if there is
more work to do. This happens from the guts of the schedule()
function. On RT this must be outside and the accessed data structures
are not protected against scheduling due to the spinlock to rtmutex
conversion. So the naive solution to this was to move the code outside
of the scheduler and protect the data structures by the pool
lock. That approach turned out to be a little naive as we cannot call
into that code when the thread blocks on a lock, as it is not allowed
to block on two locks in parallel. So we dont call into the worker
wakeup magic when the worker is blocked on a lock, which causes the
deadlock/stall observed by Austin and Mike.
Looking deeper into that worker code it turns out that the only
relevant data structure which needs to be protected is the list of
idle workers which can be woken up.
So the solution is to protect the list manipulation operations with
preempt_enable/disable pairs on RT and call unconditionally into the
worker code even when the worker is blocked on a lock. The preemption
protection is safe as there is nothing which can fiddle with the list
outside of thread context.
Reported-and_tested-by: Austin Schuh <austin@peloton-tech.com>
Reported-and_tested-by: Mike Galbraith <umgwanakikbuti@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: http://vger.kernel.org/r/alpine.DEB.2.10.1406271249510.5170@nanos
Cc: Richard Weinberger <richard.weinberger@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: stable-rt@vger.kernel.org
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
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I talked with Peter Zijlstra about this, and he told me that the clearing
of the PF_NO_SETAFFINITY flag was to deal with the optimization of
migrate_disable/enable() that ignores tasks that have that flag set. But
that optimization was removed when I did a rework of the cpu hotplug code.
I found that ignoring tasks that had that flag set would cause those tasks
to not sync with the hotplug code and cause the kernel to crash. Thus it
needed to not treat them special and those tasks had to go though the same
work as tasks without that flag set.
Now that those tasks are not treated special, there's no reason to clear the
flag.
May still need to be tested as the migrate_me() code does not ignore those
flags.
Cc: stable-rt@vger.kernel.org
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Clark Williams <williams@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20140701111444.0cfebaa1@gandalf.local.home
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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switch_hrtimer_base()"
In an rt-kernel with CONFIG_MISSED_TIMER_OFFSETS_HIST enabled,
__hrtimer_start_range_ns() now crashes, as new_base is not assigned
before it is used.
Tested-by: Carsten Emde <C.Emde@osadl.org>
Cc: stable-rt@vger.kernel.org
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
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This will void a warning comming from the spin-lock debugging code. The
lock avoiding idea is from Steven Rostedt.
Cc: stable-rt@vger.kernel.org
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
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This reverts commit ff9c870c3e27d58c9512fad122e91436681fee5a.
Cc: stable-rt@vger.kernel.org
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
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This reverts commit 4a77edc195f0b03644e84dda00fcfe9827868e8e.
This commit was added to the -rt tree and submitted to stable. But because
the stable version inserted pci_disable_device() in a slightly different
location, when stable was merged it caused this to be duplicated.
Remove the version that was added to -rt and keep the stable one.
Link: http://lkml.kernel.org/r/1403149603.5189.10.camel@marge.simpson.net
Reported-by: Mike Galbraith <umgwanakikbuti@gmail.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
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The patch "net: gianfar: do not try to cleanup TX packets if they are
not done" for 3.12-rt left out the return value for gfar_clean_tx_ring().
This would cause an error when building this module. Note, this module
does not build on x86 and was not tested because of that.
Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
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The changes to move the migrate_disable() down in the trylocks()
caused race conditions to appear in the cpu hotplug code. The
migrate disables must be done before any of the rtmutexes are
taken, otherwise a lock may be held that prevents hotplug from
moving forward.
Link: http://lkml.kernel.org/r/20140429201308.63292691@gandalf.local.home
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Nicholas Mc Guire <der.herr@hofr.at>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: linux-rt-users <linux-rt-users@vger.kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: John Kacur <jkacur@redhat.com>
Cc: Clark Williams <williams@redhat.com>
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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/n/tip-8vdw4bfcsds27cvox6rpb334@git.kernel.org
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It uses anon semaphores
|drivers/md/bcache/request.c: In function ‘cached_dev_write_complete’:
|drivers/md/bcache/request.c:1007:2: error: implicit declaration of function ‘up_read_non_owner’ [-Werror=implicit-function-declaration]
| up_read_non_owner(&dc->writeback_lock);
| ^
|drivers/md/bcache/request.c: In function ‘request_write’:
|drivers/md/bcache/request.c:1033:2: error: implicit declaration of function ‘down_read_non_owner’ [-Werror=implicit-function-declaration]
| down_read_non_owner(&dc->writeback_lock);
| ^
either we get rid of those or we have to introduce them…
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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The ntp code for notify_cmos_timer() is called from a hard interrupt
context. schedule_delayed_work() under PREEMPT_RT_FULL calls spinlocks
that have been converted to mutexes, thus calling schedule_delayed_work()
from interrupt is not safe.
Add a helper thread that does the call to schedule_delayed_work and wake
up that thread instead of calling schedule_delayed_work() directly.
This is only for CONFIG_PREEMPT_RT_FULL, otherwise the code still calls
schedule_delayed_work() directly in irq context.
Note: There's a few places in the kernel that do this. Perhaps the RT
code should have a dedicated thread that does the checks. Just register
a notifier on boot up for your check and wake up the thread when
needed. This will be a todo.
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
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Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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Completions have no long lasting callbacks and therefor do not need
the complex waitqueue variant. Use simple waitqueues which reduces the
contention on the waitqueue lock.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Merged Steven's
static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp) {
- swait_wake(&rnp->nocb_gp_wq[rnp->completed & 0x1]);
+ wake_up_all(&rnp->nocb_gp_wq[rnp->completed & 0x1]);
}
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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The function "swait_head_has_waiters()" was internalized into
wait-simple.c but it parallels the waitqueue_active of normal
waitqueue support. Given that there are over 150 waitqueue_active
users in drivers/ fs/ kernel/ and the like, lets make it globally
visible, and rename it to parallel the waitqueue_active accordingly.
We'll need to do this if we expect to expand its usage beyond RT.
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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wait_queue is a swiss army knife and in most of the cases the
complexity is not needed. For RT waitqueues are a constant source of
trouble as we can't convert the head lock to a raw spinlock due to
fancy and long lasting callbacks.
Provide a slim version, which allows RT to replace wait queues. This
should go mainline as well, as it lowers memory consumption and
runtime overhead.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
smp_mb() added by Steven Rostedt to fix a race condition with swait
wakeups vs adding items to the list.
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| CC init/main.o
|In file included from include/linux/mmzone.h:9:0,
| from include/linux/gfp.h:4,
| from include/linux/kmod.h:22,
| from include/linux/module.h:13,
| from init/main.c:15:
|include/linux/wait.h: In function ‘wait_on_atomic_t’:
|include/linux/wait.h:982:2: error: implicit declaration of function ‘atomic_read’ [-Werror=implicit-function-declaration]
| if (atomic_read(val) == 0)
| ^
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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This tracepoint is responsible for:
|[<814cc358>] __schedule_bug+0x4d/0x59
|[<814d24cc>] __schedule+0x88c/0x930
|[<814d3b90>] ? _raw_spin_unlock_irqrestore+0x40/0x50
|[<814d3b95>] ? _raw_spin_unlock_irqrestore+0x45/0x50
|[<810b57b5>] ? task_blocks_on_rt_mutex+0x1f5/0x250
|[<814d27d9>] schedule+0x29/0x70
|[<814d3423>] rt_spin_lock_slowlock+0x15b/0x278
|[<814d3786>] rt_spin_lock+0x26/0x30
|[<a00dced9>] gen6_gt_force_wake_get+0x29/0x60 [i915]
|[<a00e183f>] gen6_ring_get_irq+0x5f/0x100 [i915]
|[<a00b2a33>] ftrace_raw_event_i915_gem_ring_dispatch+0xe3/0x100 [i915]
|[<a00ac1b3>] i915_gem_do_execbuffer.isra.13+0xbd3/0x1430 [i915]
|[<810f8943>] ? trace_buffer_unlock_commit+0x43/0x60
|[<8113e8d2>] ? ftrace_raw_event_kmem_alloc+0xd2/0x180
|[<8101d063>] ? native_sched_clock+0x13/0x80
|[<a00acf29>] i915_gem_execbuffer2+0x99/0x280 [i915]
|[<a00114a3>] drm_ioctl+0x4c3/0x570 [drm]
|[<8101d0d9>] ? sched_clock+0x9/0x10
|[<a00ace90>] ? i915_gem_execbuffer+0x480/0x480 [i915]
|[<810f1c18>] ? rb_commit+0x68/0xa0
|[<810f1c6c>] ? ring_buffer_unlock_commit+0x1c/0xa0
|[<81197467>] do_vfs_ioctl+0x97/0x540
|[<81021318>] ? ftrace_raw_event_sys_enter+0xd8/0x130
|[<811979a1>] sys_ioctl+0x91/0xb0
|[<814db931>] tracesys+0xe1/0xe6
Chris Wilson does not like to move i915_trace_irq_get() out of the macro
|No. This enables the IRQ, as well as making a number of
|very expensively serialised read, unconditionally.
so it is gone now on RT.
Cc: stable-rt@vger.kernel.org
Reported-by: Joakim Hernberg <jbh@alchemy.lu>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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The opencode part is gone in 1f83fee0 ("drm/i915: clear up wedged transitions")
the owner check is still there.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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Luis captured the following:
| BUG: sleeping function called from invalid context at kernel/rtmutex.c:659
| in_atomic(): 1, irqs_disabled(): 0, pid: 517, name: Xorg
| 2 locks held by Xorg/517:
| #0:
| (
| &dev->vbl_lock
| ){......}
| , at:
| [<ffffffffa0024c60>] drm_vblank_get+0x30/0x2b0 [drm]
| #1:
| (
| &dev->vblank_time_lock
| ){......}
| , at:
| [<ffffffffa0024ce1>] drm_vblank_get+0xb1/0x2b0 [drm]
| Preemption disabled at:
| [<ffffffffa008bc95>] i915_get_vblank_timestamp+0x45/0xa0 [i915]
| CPU: 3 PID: 517 Comm: Xorg Not tainted 3.10.10-rt7+ #5
| Call Trace:
| [<ffffffff8164b790>] dump_stack+0x19/0x1b
| [<ffffffff8107e62f>] __might_sleep+0xff/0x170
| [<ffffffff81651ac4>] rt_spin_lock+0x24/0x60
| [<ffffffffa0084e67>] i915_read32+0x27/0x170 [i915]
| [<ffffffffa008a591>] i915_pipe_enabled+0x31/0x40 [i915]
| [<ffffffffa008a6be>] i915_get_crtc_scanoutpos+0x3e/0x1b0 [i915]
| [<ffffffffa00245d4>] drm_calc_vbltimestamp_from_scanoutpos+0xf4/0x430 [drm]
| [<ffffffffa008bc95>] i915_get_vblank_timestamp+0x45/0xa0 [i915]
| [<ffffffffa0024998>] drm_get_last_vbltimestamp+0x48/0x70 [drm]
| [<ffffffffa0024db5>] drm_vblank_get+0x185/0x2b0 [drm]
| [<ffffffffa0025d03>] drm_wait_vblank+0x83/0x5d0 [drm]
| [<ffffffffa00212a2>] drm_ioctl+0x552/0x6a0 [drm]
| [<ffffffff811a0095>] do_vfs_ioctl+0x325/0x5b0
| [<ffffffff811a03a1>] SyS_ioctl+0x81/0xa0
| [<ffffffff8165a342>] tracesys+0xdd/0xe2
After a longer thread it was decided to drop the preempt_disable()/
enable() invocations which were meant for -RT and Mario Kleiner looks
for a replacement.
Cc: stable-rt@vger.kernel.org
Reported-By: Luis Claudio R. Goncalves <lclaudio@uudg.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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On RT the trans_pcie->irq_lock lock is converted into a sleeping lock
and can't be used in primary irq handler. The lock is used in mutliple
places which means turning it into a raw lock could increase the
latency of the system.
For now both handlers are moved into the thread.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Clark Williams <clark.williams@gmail.com>
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On !RT interrupt runs with interrupts disabled. On RT it's in a
thread, so no need to disable interrupts at all.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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The lock is taken while reading two registers. On RT the first lock is
taken in hard irq where it might sleep and in the threaded irq.
The threaded irq runs in oneshot mode so the hard irq does not run until
the thread the completes so there is no reason to grab the lock.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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as it triggers:
|CPU: 0 PID: 0 Comm: swapper Not tainted 3.12.8-rt10 #141
|[<c0014aa4>] (unwind_backtrace+0x0/0xf8) from [<c0012788>] (show_stack+0x1c/0x20)
|[<c0012788>] (show_stack+0x1c/0x20) from [<c043c8dc>] (dump_stack+0x20/0x2c)
|[<c043c8dc>] (dump_stack+0x20/0x2c) from [<c004c5e8>] (__might_sleep+0x13c/0x170)
|[<c004c5e8>] (__might_sleep+0x13c/0x170) from [<c043f270>] (__rt_spin_lock+0x28/0x38)
|[<c043f270>] (__rt_spin_lock+0x28/0x38) from [<c043fa00>] (rt_read_lock+0x68/0x7c)
|[<c043fa00>] (rt_read_lock+0x68/0x7c) from [<c036cf74>] (led_trigger_event+0x2c/0x5c)
|[<c036cf74>] (led_trigger_event+0x2c/0x5c) from [<c036e0bc>] (ledtrig_cpu+0x54/0x5c)
|[<c036e0bc>] (ledtrig_cpu+0x54/0x5c) from [<c000ffd8>] (arch_cpu_idle_exit+0x18/0x1c)
|[<c000ffd8>] (arch_cpu_idle_exit+0x18/0x1c) from [<c00590b8>] (cpu_startup_entry+0xa8/0x234)
|[<c00590b8>] (cpu_startup_entry+0xa8/0x234) from [<c043b2cc>] (rest_init+0xb8/0xe0)
|[<c043b2cc>] (rest_init+0xb8/0xe0) from [<c061ebe0>] (start_kernel+0x2c4/0x380)
Cc: stable-rt@vger.kernel.org
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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It has become an obsession to mitigate the determinism vs. throughput
loss of RT. Looking at the mainline semantics of preemption points
gives a hint why RT sucks throughput wise for ordinary SCHED_OTHER
tasks. One major issue is the wakeup of tasks which are right away
preempting the waking task while the waking task holds a lock on which
the woken task will block right after having preempted the wakee. In
mainline this is prevented due to the implicit preemption disable of
spin/rw_lock held regions. On RT this is not possible due to the fully
preemptible nature of sleeping spinlocks.
Though for a SCHED_OTHER task preempting another SCHED_OTHER task this
is really not a correctness issue. RT folks are concerned about
SCHED_FIFO/RR tasks preemption and not about the purely fairness
driven SCHED_OTHER preemption latencies.
So I introduced a lazy preemption mechanism which only applies to
SCHED_OTHER tasks preempting another SCHED_OTHER task. Aside of the
existing preempt_count each tasks sports now a preempt_lazy_count
which is manipulated on lock acquiry and release. This is slightly
incorrect as for lazyness reasons I coupled this on
migrate_disable/enable so some other mechanisms get the same treatment
(e.g. get_cpu_light).
Now on the scheduler side instead of setting NEED_RESCHED this sets
NEED_RESCHED_LAZY in case of a SCHED_OTHER/SCHED_OTHER preemption and
therefor allows to exit the waking task the lock held region before
the woken task preempts. That also works better for cross CPU wakeups
as the other side can stay in the adaptive spinning loop.
For RT class preemption there is no change. This simply sets
NEED_RESCHED and forgoes the lazy preemption counter.
Initial test do not expose any observable latency increasement, but
history shows that I've been proven wrong before :)
The lazy preemption mode is per default on, but with
CONFIG_SCHED_DEBUG enabled it can be disabled via:
# echo NO_PREEMPT_LAZY >/sys/kernel/debug/sched_features
and reenabled via
# echo PREEMPT_LAZY >/sys/kernel/debug/sched_features
The test results so far are very machine and workload dependent, but
there is a clear trend that it enhances the non RT workload
performance.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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Since it is no longer invoked from the softirq people run into OOM more
often if the priority of the RCU thread is too low. Making boosting
default on RT should help in those case and it can be switched off if
someone knows better.
Cc: stable-rt@vger.kernel.org
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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Running RCU out of softirq is a problem for some workloads that would
like to manage RCU core processing independently of other softirq work,
for example, setting kthread priority. This commit therefore moves the
RCU core work from softirq to a per-CPU/per-flavor SCHED_OTHER kthread
named rcuc. The SCHED_OTHER approach avoids the scalability problems
that appeared with the earlier attempt to move RCU core processing to
from softirq to kthreads. That said, kernels built with RCU_BOOST=y
will run the rcuc kthreads at the RCU-boosting priority.
Reported-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Mike Galbraith <bitbucket@online.de>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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