v2: - Use the simple trylock loop as suggested by PeterZ. The current allows up to 4 levels of nested slowpath spinlock calls. That should be enough for the process, soft irq, hard irq, and nmi. With the unfortunate event of nested NMIs happening with slowpath spinlock call in each of the previous level, we are going to run out of useable MCS node for queuing. In this case, we fall back to a simple TAS lock and spin on the lock cacheline until the lock is free. This is not most elegant solution but is simple enough. Patch 1 implements the TAS loop when all the existing MCS nodes are occupied. Patches 2-4 enhances the locking statistics code to track the new code as well as enabling it on other architectures such as ARM64. By setting MAX_NODES to 1, we can have some usage of the new code path during the booting process as demonstrated by the stat counter values shown below on an 1-socket 22-core 44-thread x86-64 system after booting up the new kernel. lock_no_node=20 lock_pending=29660 lock_slowpath=172714 Waiman Long (4): locking/qspinlock: Handle > 4 slowpath nesting levels locking/qspinlock_stat: Track the no MCS node available case locking/qspinlock_stat: Separate out the PV specific stat counts locking/qspinlock_stat: Allow QUEUED_LOCK_STAT for all archs arch/Kconfig | 7 ++ arch/x86/Kconfig | 8 --- kernel/locking/qspinlock.c | 18 ++++- kernel/locking/qspinlock_stat.h | 150 +++++++++++++++++++++++++--------------- 4 files changed, 120 insertions(+), 63 deletions(-) -- 1.8.3.1
