When invoke synchronize_srcu(), in the srcu_might_be_idle(), the current CPU's sdp->lock will be acquired to check whether there are pending callbacks in the sdp->srcu_cblist, if there are no pending callbacks, probabilistically probe global state to decide whether to convert to synchronize_srcu_expedited() call. however, for the rcupdate.rcu_normal=1 kernels and after the rcu_set_runtime_mode() is called, invoke the rcu_gp_is_normal() is always return true, this mean that invoke the synchronize_srcu_expedited() always fall back to synchronize_srcu(), so there is no need to acquire sdp->lock to check sdp->srcu_cblist and probe global state in srcu_might_be_idle(). This commit therefore make srcu_might_be_idle() return immediately if the rcu_gp_is_normal() return true. Signed-off-by: Zqiang <qiang.zhang1211@xxxxxxxxx> --- kernel/rcu/srcutree.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c index 20d7a238d675..aea49cb60a45 100644 --- a/kernel/rcu/srcutree.c +++ b/kernel/rcu/srcutree.c @@ -1172,6 +1172,8 @@ static bool srcu_might_be_idle(struct srcu_struct *ssp) unsigned long tlast; check_init_srcu_struct(ssp); + if (rcu_gp_is_normal()) + return false; /* If the local srcu_data structure has callbacks, not idle. */ sdp = raw_cpu_ptr(ssp->sda); spin_lock_irqsave_rcu_node(sdp, flags); -- 2.17.1
