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>

1 files changed, 1 insertions, 3 deletions

diff --git a/kernel/softirq.c b/kernel/softirq.c
index b50990a5bea0..b9b2d4906848 100644
--- 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();