From 25e2d8c1b9e327ed260edd13169cc22bc7a78bc6 Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Tue, 25 Apr 2017 16:10:48 +0200 Subject: [PATCH] sched/cputime: Fix ksoftirqd cputime accounting regression 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 Signed-off-by: Frederic Weisbecker Reviewed-by: Rik van Riel Acked-by: Jesper Dangaard Brouer Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Stanislaw Gruszka Cc: Thomas Gleixner Cc: Wanpeng Li Link: http://lkml.kernel.org/r/1493129448-5356-1-git-send-email-fweisbec@gmail.com Signed-off-by: Ingo Molnar --- 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; -- 2.20.1