user/sven/linux.git/kernel/locking/rtmutex.c, branch leds/master

Merge branch 'sched-locking-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2015-06-24T21:46:01Z

Pull locking updates from Thomas Gleixner: "These locking updates depend on the alreay merged sched/core branch: - Lockless top waiter wakeup for rtmutex (Davidlohr) - Reduce hash bucket lock contention for PI futexes (Sebastian) - Documentation update (Davidlohr)" * 'sched-locking-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: locking/rtmutex: Update stale plist comments futex: Lower the lock contention on the HB lock during wake up locking/rtmutex: Implement lockless top-waiter wakeup

Merge branch 'timers-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2015-06-23T01:57:44Z

Pull timer updates from Thomas Gleixner: "A rather largish update for everything time and timer related: - Cache footprint optimizations for both hrtimers and timer wheel - Lower the NOHZ impact on systems which have NOHZ or timer migration disabled at runtime. - Optimize run time overhead of hrtimer interrupt by making the clock offset updates smarter - hrtimer cleanups and removal of restrictions to tackle some problems in sched/perf - Some more leap second tweaks - Another round of changes addressing the 2038 problem - First step to change the internals of clock event devices by introducing the necessary infrastructure - Allow constant folding for usecs/msecs_to_jiffies() - The usual pile of clockevent/clocksource driver updates The hrtimer changes contain updates to sched, perf and x86 as they depend on them plus changes all over the tree to cleanup API changes and redundant code, which got copied all over the place. The y2038 changes touch s390 to remove the last non 2038 safe code related to boot/persistant clock" * 'timers-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (114 commits) clocksource: Increase dependencies of timer-stm32 to limit build wreckage timer: Minimize nohz off overhead timer: Reduce timer migration overhead if disabled timer: Stats: Simplify the flags handling timer: Replace timer base by a cpu index timer: Use hlist for the timer wheel hash buckets timer: Remove FIFO "guarantee" timers: Sanitize catchup_timer_jiffies() usage hrtimer: Allow hrtimer::function() to free the timer seqcount: Introduce raw_write_seqcount_barrier() seqcount: Rename write_seqcount_barrier() hrtimer: Fix hrtimer_is_queued() hole hrtimer: Remove HRTIMER_STATE_MIGRATE selftest: Timers: Avoid signal deadlock in leap-a-day timekeeping: Copy the shadow-timekeeper over the real timekeeper last clockevents: Check state instead of mode in suspend/resume path selftests: timers: Add leap-second timer edge testing to leap-a-day.c ntp: Do leapsecond adjustment in adjtimex read path time: Prevent early expiry of hrtimers[CLOCK_REALTIME] at the leap second edge ntp: Introduce and use SECS_PER_DAY macro instead of 86400 ...

Merge branch 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2015-06-22T21:54:22Z

Pull locking updates from Ingo Molnar: "The main changes are: - 'qspinlock' support, enabled on x86: queued spinlocks - these are now the spinlock variant used by x86 as they outperform ticket spinlocks in every category. (Waiman Long) - 'pvqspinlock' support on x86: paravirtualized variant of queued spinlocks. (Waiman Long, Peter Zijlstra) - 'qrwlock' support, enabled on x86: queued rwlocks. Similar to queued spinlocks, they are now the variant used by x86: CONFIG_ARCH_USE_QUEUED_SPINLOCKS=y CONFIG_QUEUED_SPINLOCKS=y CONFIG_ARCH_USE_QUEUED_RWLOCKS=y CONFIG_QUEUED_RWLOCKS=y - various lockdep fixlets - various locking primitives cleanups, further WRITE_ONCE() propagation" * 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (24 commits) locking/lockdep: Remove hard coded array size dependency locking/qrwlock: Don't contend with readers when setting _QW_WAITING lockdep: Do not break user-visible string locking/arch: Rename set_mb() to smp_store_mb() locking/arch: Add WRITE_ONCE() to set_mb() rtmutex: Warn if trylock is called from hard/softirq context arch: Remove __ARCH_HAVE_CMPXCHG locking/rtmutex: Drop usage of __HAVE_ARCH_CMPXCHG locking/qrwlock: Rename QUEUE_RWLOCK to QUEUED_RWLOCKS locking/pvqspinlock: Rename QUEUED_SPINLOCK to QUEUED_SPINLOCKS locking/pvqspinlock: Replace xchg() by the more descriptive set_mb() locking/pvqspinlock, x86: Enable PV qspinlock for Xen locking/pvqspinlock, x86: Enable PV qspinlock for KVM locking/pvqspinlock, x86: Implement the paravirt qspinlock call patching locking/pvqspinlock: Implement simple paravirt support for the qspinlock locking/qspinlock: Revert to test-and-set on hypervisors locking/qspinlock: Use a simple write to grab the lock locking/qspinlock: Optimize for smaller NR_CPUS locking/qspinlock: Extract out code snippets for the next patch locking/qspinlock: Add pending bit ...

locking/rtmutex: Update stale plist comments

2015-06-19T19:27:21Z

... as of fb00aca4744 (rtmutex: Turn the plist into an rb-tree) we no longer use plists for queuing any waiters. Update stale comments. Signed-off-by: Davidlohr Bueso Cc: Steven Rostedt Cc: Mike Galbraith Cc: Paul E. McKenney Cc: Sebastian Andrzej Siewior Cc: Davidlohr Bueso Cc: Peter Zijlstra Link: http://lkml.kernel.org/r/1432056298-18738-4-git-send-email-dave@stgolabs.net Signed-off-by: Thomas Gleixner

futex: Lower the lock contention on the HB lock during wake up

2015-06-19T19:26:38Z

wake_futex_pi() wakes the task before releasing the hash bucket lock (HB). The first thing the woken up task usually does is to acquire the lock which requires the HB lock. On SMP Systems this leads to blocking on the HB lock which is released by the owner shortly after. This patch rearranges the unlock path by first releasing the HB lock and then waking up the task. [ tglx: Fixed up the rtmutex unlock path ] Originally-from: Thomas Gleixner Signed-off-by: Sebastian Andrzej Siewior Cc: Peter Zijlstra Cc: Steven Rostedt Cc: Mike Galbraith Cc: Paul E. McKenney Cc: Davidlohr Bueso Link: http://lkml.kernel.org/r/20150617083350.GA2433@linutronix.de Signed-off-by: Thomas Gleixner

locking/rtmutex: Implement lockless top-waiter wakeup

2015-06-18T20:27:46Z

Mark the task for later wakeup after the wait_lock has been released. This way, once the next task is awoken, it will have a better chance to of finding the wait_lock free when continuing executing in __rt_mutex_slowlock() when trying to acquire the rtmutex, calling try_to_take_rt_mutex(). Upon contended scenarios, other tasks attempting take the lock may acquire it first, right after the wait_lock is released, but (a) this can also occur with the current code, as it relies on the spinlock fairness, and (b) we are dealing with the top-waiter anyway, so it will always take the lock next. Signed-off-by: Davidlohr Bueso Cc: Steven Rostedt Cc: Mike Galbraith Cc: Paul E. McKenney Cc: Sebastian Andrzej Siewior Cc: Davidlohr Bueso Cc: Peter Zijlstra Link: http://lkml.kernel.org/r/1432056298-18738-2-git-send-email-dave@stgolabs.net Signed-off-by: Thomas Gleixner

Merge branch 'linus' into timers/core

2015-05-19T14:12:32Z

Make sure the upstream fixes are applied before adding further modifications.

rtmutex: Warn if trylock is called from hard/softirq context

2015-05-13T20:49:12Z

rt_mutex_trylock() must be called from thread context. It can be called from atomic regions (preemption or interrupts disabled), but not from hard/softirq/nmi context. Add a warning to alert abusers. The reasons for this are: 1) There is a potential deadlock in the slowpath 2) Another cpu which blocks on the rtmutex will boost the task which allegedly locked the rtmutex, but that cannot work because the hard/softirq context borrows the task context. Signed-off-by: Thomas Gleixner Cc: Peter Zijlstra Cc: Sebastian Siewior

locking/rtmutex: Drop usage of __HAVE_ARCH_CMPXCHG

2015-05-13T08:51:28Z

The rtmutex code is the only user of __HAVE_ARCH_CMPXCHG and we have a few other user of cmpxchg() which do not care about __HAVE_ARCH_CMPXCHG. This define was first introduced in 23f78d4a0 ("[PATCH] pi-futex: rt mutex core") which is v2.6.18. The generic cmpxchg was introduced later in 068fbad288 ("Add cmpxchg_local to asm-generic for per cpu atomic operations") which is v2.6.25. Back then something was required to get rtmutex working with the fast path on architectures without cmpxchg and this seems to be the result. It popped up recently on rt-users because ARM (v6+) does not define __HAVE_ARCH_CMPXCHG (even that it implements it) which results in slower locking performance in the fast path. To put some numbers on it: preempt -RT, am335x, 10 loops of 100000 invocations of rt_spin_lock() + rt_spin_unlock() (time "total" is the average of the 10 loops for the 100000 invocations, "loop" is "total / 100000 * 1000"): cmpxchg | slowpath used || cmpxchg used | total | loop || total | loop --------|-----------|-------||------------|------- ARMv6 | 9129.4 us | 91 ns || 3311.9 us | 33 ns generic | 9360.2 us | 94 ns || 10834.6 us | 108 ns ----------------------------||-------------------- Forcing it to generic cmpxchg() made things worse for the slowpath and even worse in cmpxchg() path. It boils down to 14ns more per lock+unlock in a cache hot loop so it might not be that much in real world. The last test was a substitute for pre ARMv6 machine but then I was able to perform the comparison on imx28 which is ARMv5 and therefore is always is using the generic cmpxchg implementation. And the numbers: | total | loop -------- |----------- |-------- slowpath | 263937.2 us | 2639 ns cmpxchg | 16934.2 us | 169 ns -------------------------------- The numbers are larger since the machine is slower in general. However, letting rtmutex use cmpxchg() instead the slowpath seem to improve things. Since from the ARM (tested on am335x + imx28) point of view always using cmpxchg() in rt_mutex_lock() + rt_mutex_unlock() makes sense I would drop the define. Signed-off-by: Sebastian Andrzej Siewior Cc: Arnd Bergmann Cc: Peter Zijlstra Cc: will.deacon@arm.com Cc: linux-arm-kernel@lists.infradead.org Link: http://lkml.kernel.org/r/20150225175613.GE6823@linutronix.de Signed-off-by: Thomas Gleixner

sched: Handle priority boosted tasks proper in setscheduler()

2015-05-08T09:53:55Z

Ronny reported that the following scenario is not handled correctly: T1 (prio = 10) lock(rtmutex); T2 (prio = 20) lock(rtmutex) boost T1 T1 (prio = 20) sys_set_scheduler(prio = 30) T1 prio = 30 .... sys_set_scheduler(prio = 10) T1 prio = 30 The last step is wrong as T1 should now be back at prio 20. Commit c365c292d059 ("sched: Consider pi boosting in setscheduler()") only handles the case where a boosted tasks tries to lower its priority. Fix it by taking the new effective priority into account for the decision whether a change of the priority is required. Reported-by: Ronny Meeus Tested-by: Steven Rostedt Signed-off-by: Thomas Gleixner Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Steven Rostedt Cc: Cc: Borislav Petkov Cc: H. Peter Anvin Cc: Mike Galbraith Fixes: c365c292d059 ("sched: Consider pi boosting in setscheduler()") Link: http://lkml.kernel.org/r/alpine.DEB.2.11.1505051806060.4225@nanos Signed-off-by: Ingo Molnar