> 在 2016年6月26日，18:41，Pan Xinhui <xinhui....@linux.vnet.ibm.com> 写道：
>
> 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 <xinhui....@linux.vnet.ibm.com>
> ---
> 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));
> +
OK, one mistake ,
should be
if (prev != prev_old) {
prev_old = prev;
yield_count = vcpu_get_yield_count(node_cpu(prev));
}
> cpu_relax_lowlatency();
> }
> return true;
> --
> 2.4.11
>
