4.9-stable review patch. If anyone has any objections, please let me know.
------------------
From: Frederic Weisbecker fweisbec@gmail.com
commit 25e2d8c1b9e327ed260edd13169cc22bc7a78bc6 upstream.
irq_time_read() returns the irqtime minus the ksoftirqd time. This is necessary because irq_time_read() is used to substract the IRQ time from the sum_exec_runtime of a task. If we were to include the softirq time of ksoftirqd, this task would substract its own CPU time everytime it updates ksoftirqd->sum_exec_runtime which would therefore never progress.
But this behaviour got broken by:
a499a5a14db ("sched/cputime: Increment kcpustat directly on irqtime account")
... which now includes ksoftirqd softirq time in the time returned by irq_time_read().
This has resulted in wrong ksoftirqd cputime reported to userspace through /proc/stat and thus "top" not showing ksoftirqd when it should after intense networking load.
ksoftirqd->stime happens to be correct but it gets scaled down by sum_exec_runtime through task_cputime_adjusted().
To fix this, just account the strict IRQ time in a separate counter and use it to report the IRQ time.
Reported-and-tested-by: Jesper Dangaard Brouer brouer@redhat.com Signed-off-by: Frederic Weisbecker fweisbec@gmail.com Reviewed-by: Rik van Riel riel@redhat.com Acked-by: Jesper Dangaard Brouer brouer@redhat.com Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Peter Zijlstra peterz@infradead.org Cc: Stanislaw Gruszka sgruszka@redhat.com Cc: Thomas Gleixner tglx@linutronix.de Cc: Wanpeng Li wanpeng.li@hotmail.com Link: http://lkml.kernel.org/r/1493129448-5356-1-git-send-email-fweisbec@gmail.com Signed-off-by: Ingo Molnar mingo@kernel.org Signed-off-by: Ivan Delalande colona@arista.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- kernel/sched/cputime.c | 27 ++++++++++++++++----------- kernel/sched/sched.h | 9 +++++++-- 2 files changed, 23 insertions(+), 13 deletions(-)
--- a/kernel/sched/cputime.c +++ b/kernel/sched/cputime.c @@ -37,6 +37,18 @@ 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. @@ -44,7 +56,6 @@ 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;
@@ -55,22 +66,16 @@ void irqtime_account_irq(struct task_str 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);
--- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -1743,6 +1743,7 @@ static inline void nohz_balance_exit_idl
#ifdef CONFIG_IRQ_TIME_ACCOUNTING struct irqtime { + u64 total; u64 tick_delta; u64 irq_start_time; struct u64_stats_sync sync; @@ -1750,16 +1751,20 @@ 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;