An over-committed guest with more vCPUs than pCPUs has a heavy overload in osq_lock().
This is because vCPU A hold the osq lock and yield out, vCPU B wait per_cpu node->locked to be set. IOW, vCPU B wait vCPU A to run and unlock the osq lock. So lets also use neet_yield_to() to detect if we need stop the spinning Signed-off-by: Pan Xinhui <[email protected]> --- kernel/locking/osq_lock.c | 18 +++++++++++++++--- 1 file changed, 15 insertions(+), 3 deletions(-) diff --git a/kernel/locking/osq_lock.c b/kernel/locking/osq_lock.c index 05a3785..4287603 100644 --- a/kernel/locking/osq_lock.c +++ b/kernel/locking/osq_lock.c @@ -21,6 +21,11 @@ static inline int encode_cpu(int cpu_nr) return cpu_nr + 1; } +static inline int node_cpu(struct optimistic_spin_node *node) +{ + return node->cpu - 1; +} + static inline struct optimistic_spin_node *decode_cpu(int encoded_cpu_val) { int cpu_nr = encoded_cpu_val - 1; @@ -84,9 +89,10 @@ osq_wait_next(struct optimistic_spin_queue *lock, bool osq_lock(struct optimistic_spin_queue *lock) { struct optimistic_spin_node *node = this_cpu_ptr(&osq_node); - struct optimistic_spin_node *prev, *next; + struct optimistic_spin_node *prev, *next, *prev_old; int curr = encode_cpu(smp_processor_id()); int old; + unsigned int yield_count; node->locked = 0; node->next = NULL; @@ -114,14 +120,20 @@ bool osq_lock(struct optimistic_spin_queue *lock) * guaranteed their existence -- this allows us to apply * cmpxchg in an attempt to undo our queueing. */ - + prev_old = prev; + yield_count = vcpu_get_yield_count(node_cpu(prev)); while (!READ_ONCE(node->locked)) { /* * If we need to reschedule bail... so we can block. */ - if (need_resched()) + if (need_resched() || + need_yield_to(node_cpu(prev), yield_count)) goto unqueue; + prev = READ_ONCE(node->prev); + if (prev != prev_old) + yield_count = vcpu_get_yield_count(node_cpu(prev)); + cpu_relax_lowlatency(); } return true; -- 2.4.11
