3 files changed, 76 insertions, 19 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 75205391b335..bad5987c4727 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1284,6 +1284,19 @@ running once the system is up.
                         New name for the ramdisk parameter.
                         See Documentation/ramdisk.txt.
 
+        rcu.blimit=     [KNL,BOOT] Set maximum number of finished
+                        RCU callbacks to process in one batch.
+
+        rcu.qhimark=    [KNL,BOOT] Set threshold of queued
+                        RCU callbacks over which batch limiting is disabled.
+
+        rcu.qlowmark=   [KNL,BOOT] Set threshold of queued
+                        RCU callbacks below which batch limiting is re-enabled.
+
+        rcu.rsinterval= [KNL,BOOT,SMP] Set the number of additional
+                        RCU callbacks to queued before forcing reschedule
+                        on all cpus.
+
         rdinit=         [KNL]
                         Format: <full_path>
                         Run specified binary instead of /init from the ramdisk,
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index b87aefa082e2..c2ec6c77874e 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -98,13 +98,17 @@ struct rcu_data {
         long            batch;           /* Batch # for current RCU batch */
         struct rcu_head *nxtlist;
         struct rcu_head **nxttail;
-        long            count; /* # of queued items */
+        long            qlen;            /* # of queued callbacks */
         struct rcu_head *curlist;
         struct rcu_head **curtail;
         struct rcu_head *donelist;
         struct rcu_head **donetail;
+        long            blimit;          /* Upper limit on a processed batch */
         int cpu;
         struct rcu_head barrier;
+#ifdef CONFIG_SMP
+        long            last_rs_qlen;    /* qlen during the last resched */
+#endif
 };
 
 DECLARE_PER_CPU(struct rcu_data, rcu_data);
diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c
index 0cf8146bd585..8cf15a569fcd 100644
--- a/kernel/rcupdate.c
+++ b/kernel/rcupdate.c
@@ -67,7 +67,43 @@ DEFINE_PER_CPU(struct rcu_data, rcu_bh_data) = { 0L };
 
 /* Fake initialization required by compiler */
 static DEFINE_PER_CPU(struct tasklet_struct, rcu_tasklet) = {NULL};
-static int maxbatch = 10000;
+static int blimit = 10;
+static int qhimark = 10000;
+static int qlowmark = 100;
+#ifdef CONFIG_SMP
+static int rsinterval = 1000;
+#endif
+
+static atomic_t rcu_barrier_cpu_count;
+static struct semaphore rcu_barrier_sema;
+static struct completion rcu_barrier_completion;
+
+#ifdef CONFIG_SMP
+static void force_quiescent_state(struct rcu_data *rdp,
+                        struct rcu_ctrlblk *rcp)
+{
+        int cpu;
+        cpumask_t cpumask;
+        set_need_resched();
+        if (unlikely(rdp->qlen - rdp->last_rs_qlen > rsinterval)) {
+                rdp->last_rs_qlen = rdp->qlen;
+                /*
+                 * Don't send IPI to itself. With irqs disabled,
+                 * rdp->cpu is the current cpu.
+                 */
+                cpumask = rcp->cpumask;
+                cpu_clear(rdp->cpu, cpumask);
+                for_each_cpu_mask(cpu, cpumask)
+                        smp_send_reschedule(cpu);
+        }
+}
+#else
+static inline void force_quiescent_state(struct rcu_data *rdp,
+                        struct rcu_ctrlblk *rcp)
+{
+        set_need_resched();
+}
+#endif
 
 /**
  * call_rcu - Queue an RCU callback for invocation after a grace period.
@@ -92,17 +128,13 @@ void fastcall call_rcu(struct rcu_head *head,
         rdp = &__get_cpu_var(rcu_data);
         *rdp->nxttail = head;
         rdp->nxttail = &head->next;
-
-        if (unlikely(++rdp->count > 10000))
-                set_need_resched();
-
+        if (unlikely(++rdp->qlen > qhimark)) {
+                rdp->blimit = INT_MAX;
+                force_quiescent_state(rdp, &rcu_ctrlblk);
+        }
         local_irq_restore(flags);
 }
 
-static atomic_t rcu_barrier_cpu_count;
-static struct semaphore rcu_barrier_sema;
-static struct completion rcu_barrier_completion;
-
 /**
  * call_rcu_bh - Queue an RCU for invocation after a quicker grace period.
  * @head: structure to be used for queueing the RCU updates.
@@ -131,12 +163,12 @@ void fastcall call_rcu_bh(struct rcu_head *head,
         rdp = &__get_cpu_var(rcu_bh_data);
         *rdp->nxttail = head;
         rdp->nxttail = &head->next;
-        rdp->count++;
-/*
- *  Should we directly call rcu_do_batch() here ?
- *  if (unlikely(rdp->count > 10000))
- *      rcu_do_batch(rdp);
- */
+
+        if (unlikely(++rdp->qlen > qhimark)) {
+                rdp->blimit = INT_MAX;
+                force_quiescent_state(rdp, &rcu_bh_ctrlblk);
+        }
+
         local_irq_restore(flags);
 }
 
@@ -199,10 +231,12 @@ static void rcu_do_batch(struct rcu_data *rdp)
                 next = rdp->donelist = list->next;
                 list->func(list);
                 list = next;
-                rdp->count--;
-                if (++count >= maxbatch)
+                rdp->qlen--;
+                if (++count >= rdp->blimit)
                         break;
         }
+        if (rdp->blimit == INT_MAX && rdp->qlen <= qlowmark)
+                rdp->blimit = blimit;
         if (!rdp->donelist)
                 rdp->donetail = &rdp->donelist;
         else
@@ -473,6 +507,7 @@ static void rcu_init_percpu_data(int cpu, struct rcu_ctrlblk *rcp,
         rdp->quiescbatch = rcp->completed;
         rdp->qs_pending = 0;
         rdp->cpu = cpu;
+        rdp->blimit = blimit;
 }
 
 static void __devinit rcu_online_cpu(int cpu)
@@ -567,7 +602,12 @@ void synchronize_kernel(void)
         synchronize_rcu();
 }
 
-module_param(maxbatch, int, 0);
+module_param(blimit, int, 0);
+module_param(qhimark, int, 0);
+module_param(qlowmark, int, 0);
+#ifdef CONFIG_SMP
+module_param(rsinterval, int, 0);
+#endif
 EXPORT_SYMBOL_GPL(rcu_batches_completed);
 EXPORT_SYMBOL(call_rcu);  /* WARNING: GPL-only in April 2006. */
 EXPORT_SYMBOL(call_rcu_bh);  /* WARNING: GPL-only in April 2006. */