With volatile removed from arch_raw_cpu_ptr() the compiler no longer
creates the per-CPU reference. The usage of the macro can be reverted
now.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20220328145810.86783-3-bigeasy@linutronix.de
It has been said that local_lock() does not add any overhead compared to
preempt_disable() in a !LOCKDEP configuration. A micro benchmark showed
an unexpected result which can be reduced to the fact that local_lock()
was not entirely optimized away.
In the !LOCKDEP configuration local_lock_acquire() is an empty static
inline function. On x86 the this_cpu_ptr() argument of that function is
fully evaluated leading to an additional mov+add instructions which are
not needed and not used.
Replace the static inline function with a macro. The typecheck() macro
ensures that the argument is of proper type while the resulting
disassembly shows no traces of this_cpu_ptr().
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Waiman Long <longman@redhat.com>
Link: https://lkml.kernel.org/r/YgKjciR60fZft2l4@linutronix.de
On PREEMPT_RT enabled kernels local_lock maps to a per CPU 'sleeping'
spinlock which protects the critical section while staying preemptible. CPU
locality is established by disabling migration.
Provide the necessary types and macros to substitute the non-RT variant.
Co-developed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211306.023630962@linutronix.de
If CONFIG_DEBUG_LOCK_ALLOC=y is enabled then local_lock_t has an 'owner'
member which is checked for consistency, but nothing initialized it to
zero explicitly.
The static initializer does so implicit, and the run time allocated per CPU
storage is usually zero initialized as well, but relying on that is not
really good practice.
Fixes: 91710728d1 ("locking: Introduce local_lock()")
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211301.969975279@linutronix.de
The local_lock_t's are special, because they cannot form IRQ
inversions, make sure we can tell them apart from the rest of the
locks.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
preempt_disable() and local_irq_disable/save() are in principle per CPU big
kernel locks. This has several downsides:
- The protection scope is unknown
- Violation of protection rules is hard to detect by instrumentation
- For PREEMPT_RT such sections, unless in low level critical code, can
violate the preemptability constraints.
To address this PREEMPT_RT introduced the concept of local_locks which are
strictly per CPU.
The lock operations map to preempt_disable(), local_irq_disable/save() and
the enabling counterparts on non RT enabled kernels.
If lockdep is enabled local locks gain a lock map which tracks the usage
context. This will catch cases where an area is protected by
preempt_disable() but the access also happens from interrupt context. local
locks have identified quite a few such issues over the years, the most
recent example is:
b7d5dc2107 ("random: add a spinlock_t to struct batched_entropy")
Aside of the lockdep coverage this also improves code readability as it
precisely annotates the protection scope.
PREEMPT_RT substitutes these local locks with 'sleeping' spinlocks to
protect such sections while maintaining preemtability and CPU locality.
local locks can replace:
- preempt_enable()/disable() pairs
- local_irq_disable/enable() pairs
- local_irq_save/restore() pairs
They are also used to replace code which implicitly disables preemption
like:
- get_cpu()/put_cpu()
- get_cpu_var()/put_cpu_var()
with PREEMPT_RT friendly constructs.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20200527201119.1692513-2-bigeasy@linutronix.de
Sebastian Andrzej Siewior