Hi Alex, On 2019/3/29 23:20, Alex Kogan wrote: > In CNA, spinning threads are organized in two queues, a main queue for > threads running on the same node as the current lock holder, and a > secondary queue for threads running on other nodes. At the unlock time, > the lock holder scans the main queue looking for a thread running on > the same node. If found (call it thread T), all threads in the main queue > between the current lock holder and T are moved to the end of the > secondary queue, and the lock is passed to T. If such T is not found, the > lock is passed to the first node in the secondary queue. Finally, if the > secondary queue is empty, the lock is passed to the next thread in the > main queue. For more details, see https://arxiv.org/abs/1810.05600. > > Note that this variant of CNA may introduce starvation by continuously > passing the lock to threads running on the same node. This issue > will be addressed later in the series. > > Enabling CNA is controlled via a new configuration option > (NUMA_AWARE_SPINLOCKS), which is enabled by default if NUMA is enabled. > > Signed-off-by: Alex Kogan <alex.kogan@xxxxxxxxxx> > Reviewed-by: Steve Sistare <steven.sistare@xxxxxxxxxx> > --- > arch/x86/Kconfig | 14 +++ > include/asm-generic/qspinlock_types.h | 13 +++ > kernel/locking/mcs_spinlock.h | 10 ++ > kernel/locking/qspinlock.c | 29 +++++- > kernel/locking/qspinlock_cna.h | 173 ++++++++++++++++++++++++++++++++++ > 5 files changed, 236 insertions(+), 3 deletions(-) > create mode 100644 kernel/locking/qspinlock_cna.h > (SNIP) > + > +static __always_inline int get_node_index(struct mcs_spinlock *node) > +{ > + return decode_count(node->node_and_count++); When nesting level is > 4, it won't return a index >= 4 here and the numa node number is changed by mistake. It will go into a wrong way instead of the following branch. /* * 4 nodes are allocated based on the assumption that there will * not be nested NMIs taking spinlocks. That may not be true in * some architectures even though the chance of needing more than * 4 nodes will still be extremely unlikely. When that happens, * we fall back to spinning on the lock directly without using * any MCS node. This is not the most elegant solution, but is * simple enough. */ if (unlikely(idx >= MAX_NODES)) { while (!queued_spin_trylock(lock)) cpu_relax(); goto release; } > +} > + > +static __always_inline void release_mcs_node(struct mcs_spinlock *node) > +{ > + __this_cpu_dec(node->node_and_count); > +} > + > +static __always_inline void cna_init_node(struct mcs_spinlock *node, int cpuid, > + u32 tail) > +{ Thanks, Wei
