softirq: A single rcu_bh_qs() call per softirq set is enough

Calling rcu_bh_qs() after every softirq action is not really needed.
What RCU needs is at least one rcu_bh_qs() per softirq round to note a
quiescent state was passed for rcu_bh.

Note for Paul and myself : this could be inlined as a single instruction
and avoid smp_processor_id()
(sone this_cpu_write(rcu_bh_data.passed_quiesce, 1))

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>

diff --git a/kernel/softirq.c b/kernel/softirq.c
index b50990a..b9b2d49 100644 (file)
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -232,7 +232,6 @@ asmlinkage void __do_softirq(void)
        bool in_hardirq;
        __u32 pending;
        int softirq_bit;
-       int cpu;
 
        /*
         * Mask out PF_MEMALLOC s current task context is borrowed for the
@@ -247,7 +246,6 @@ asmlinkage void __do_softirq(void)
        __local_bh_disable_ip(_RET_IP_, SOFTIRQ_OFFSET);
        in_hardirq = lockdep_softirq_start();
 
-       cpu = smp_processor_id();
 restart:
        /* Reset the pending bitmask before enabling irqs */
        set_softirq_pending(0);
@@ -276,11 +274,11 @@ restart:
                               prev_count, preempt_count());
                        preempt_count_set(prev_count);
                }
-               rcu_bh_qs(cpu);
                h++;
                pending >>= softirq_bit;
        }
 
+       rcu_bh_qs(smp_processor_id());
        local_irq_disable();
 
        pending = local_softirq_pending();