[GIT pull] scheduler fix for 4.11

[Thomas Gleixner]

Linus,

please pull the latest sched-urgent-for-linus git tree from:

   git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git 
sched-urgent-for-linus

A single fix for a cputime accounting regression whihc got introduced in
the 4.11 cycle.

Thanks,

        tglx

------------------>
Frederic Weisbecker (1):
      sched/cputime: Fix ksoftirqd cputime accounting regression


 kernel/sched/cputime.c | 27 ++++++++++++++++-----------
 kernel/sched/sched.h   |  9 +++++++--
 2 files changed, 23 insertions(+), 13 deletions(-)

diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
index f3778e2b46c8..aea3135c5d90 100644
--- a/kernel/sched/cputime.c
+++ b/kernel/sched/cputime.c
@@ -34,6 +34,18 @@ void disable_sched_clock_irqtime(void)
        sched_clock_irqtime = 0;
 }
 
+static void irqtime_account_delta(struct irqtime *irqtime, u64 delta,
+                                 enum cpu_usage_stat idx)
+{
+       u64 *cpustat = kcpustat_this_cpu->cpustat;
+
+       u64_stats_update_begin(&irqtime->sync);
+       cpustat[idx] += delta;
+       irqtime->total += delta;
+       irqtime->tick_delta += delta;
+       u64_stats_update_end(&irqtime->sync);
+}
+
 /*
  * Called before incrementing preempt_count on {soft,}irq_enter
  * and before decrementing preempt_count on {soft,}irq_exit.
@@ -41,7 +53,6 @@ void disable_sched_clock_irqtime(void)
 void irqtime_account_irq(struct task_struct *curr)
 {
        struct irqtime *irqtime = this_cpu_ptr(&cpu_irqtime);
-       u64 *cpustat = kcpustat_this_cpu->cpustat;
        s64 delta;
        int cpu;
 
@@ -52,22 +63,16 @@ void irqtime_account_irq(struct task_struct *curr)
        delta = sched_clock_cpu(cpu) - irqtime->irq_start_time;
        irqtime->irq_start_time += delta;
 
-       u64_stats_update_begin(&irqtime->sync);
        /*
         * We do not account for softirq time from ksoftirqd here.
         * We want to continue accounting softirq time to ksoftirqd thread
         * in that case, so as not to confuse scheduler with a special task
         * that do not consume any time, but still wants to run.
         */
-       if (hardirq_count()) {
-               cpustat[CPUTIME_IRQ] += delta;
-               irqtime->tick_delta += delta;
-       } else if (in_serving_softirq() && curr != this_cpu_ksoftirqd()) {
-               cpustat[CPUTIME_SOFTIRQ] += delta;
-               irqtime->tick_delta += delta;
-       }
-
-       u64_stats_update_end(&irqtime->sync);
+       if (hardirq_count())
+               irqtime_account_delta(irqtime, delta, CPUTIME_IRQ);
+       else if (in_serving_softirq() && curr != this_cpu_ksoftirqd())
+               irqtime_account_delta(irqtime, delta, CPUTIME_SOFTIRQ);
 }
 EXPORT_SYMBOL_GPL(irqtime_account_irq);
 
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 5cbf92214ad8..767aab3505a8 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1869,6 +1869,7 @@ static inline void nohz_balance_exit_idle(unsigned int 
cpu) { }
 
 #ifdef CONFIG_IRQ_TIME_ACCOUNTING
 struct irqtime {
+       u64                     total;
        u64                     tick_delta;
        u64                     irq_start_time;
        struct u64_stats_sync   sync;
@@ -1876,16 +1877,20 @@ struct irqtime {
 
 DECLARE_PER_CPU(struct irqtime, cpu_irqtime);
 
+/*
+ * Returns the irqtime minus the softirq time computed by ksoftirqd.
+ * Otherwise ksoftirqd's sum_exec_runtime is substracted its own runtime
+ * and never move forward.
+ */
 static inline u64 irq_time_read(int cpu)
 {
        struct irqtime *irqtime = &per_cpu(cpu_irqtime, cpu);
-       u64 *cpustat = kcpustat_cpu(cpu).cpustat;
        unsigned int seq;
        u64 total;
 
        do {
                seq = __u64_stats_fetch_begin(&irqtime->sync);
-               total = cpustat[CPUTIME_SOFTIRQ] + cpustat[CPUTIME_IRQ];
+               total = irqtime->total;
        } while (__u64_stats_fetch_retry(&irqtime->sync, seq));
 
        return total;