This patchset modifies the x86 qspinlock and qrwlock code to allow it to store the lock holder cpu number (lock writer cpu number for qrwlock) in the lock itself if feasible. This lock holder cpu information is useful for debugging and crash dump analysis. It may also be useful to architectures like PowerPC that needs the lock holder cpu number for better paravirtual spinlock performance. This capability is enabled on a per-architecture basis by defining the macros __cpu_number_sadd1 (for qrwlock) and __cpu_number_sadd2 (for qspinlock). These macros define the architecture's way to get to a percpu saturated +1 and +2 cpu number that can be used in the lock byte of qspinlock and qrwlock. This patchset enables it for the x86 architecture only. Additional patches can be submitted later on to enable other architectures, if desired. I have run some locking microbenchmark with and without this patch. I saw about 1% peformance degradation at low lock contention level, but about 1% performance gain at high lock contention level. That slight performance may be caused by a slight difference in the generated code and may not be entirely due to the access of the percpu variable. Anyway, that performance difference should be negligible for most real workloads. Waiman Long (5): x86/smp: Add saturated +1/+2 1-byte cpu numbers locking/pvqspinlock: Make pvqsinlock code easier to read locking/qspinlock: Pass lock value as function argument locking/qspinlock: Make qspinhlock store lock holder cpu number locking/qrwlock: Make qrwlock store writer cpu number arch/x86/include/asm/qspinlock_paravirt.h | 42 +++++++++++------------ arch/x86/include/asm/spinlock.h | 5 +++ arch/x86/kernel/setup_percpu.c | 11 ++++++ include/asm-generic/qrwlock.h | 12 ++++++- include/asm-generic/qspinlock.h | 10 ++++++ include/asm-generic/qspinlock_types.h | 2 +- kernel/locking/qrwlock.c | 11 +++--- kernel/locking/qspinlock.c | 31 ++++++++--------- kernel/locking/qspinlock_paravirt.h | 35 ++++++++++--------- 9 files changed, 97 insertions(+), 62 deletions(-) -- 2.18.1
