linux-kernel - Re: [PATCH 2/5] irqtime: Remove needless IRQs disablement on kcpustat update

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Message-ID: <20160907075913.GR10153@twins.programming.kicks-ass.net>
Date:   Wed, 7 Sep 2016 09:59:13 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Frederic Weisbecker <fweisbec@...il.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Wanpeng Li <wanpeng.li@...mail.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Ingo Molnar <mingo@...nel.org>, Mike Galbraith <efault@....de>,
        Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH 2/5] irqtime: Remove needless IRQs disablement on
 kcpustat update

On Fri, Sep 02, 2016 at 04:03:02PM +0200, Frederic Weisbecker wrote:

> diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
> index f111076..d4d12a9 100644
> --- a/kernel/sched/cputime.c
> +++ b/kernel/sched/cputime.c
> @@ -78,30 +78,26 @@ EXPORT_SYMBOL_GPL(irqtime_account_irq);
>  static cputime_t irqtime_account_hi_update(cputime_t maxtime)
>  {
>  	u64 *cpustat = kcpustat_this_cpu->cpustat;
> -	unsigned long flags;
>  	cputime_t irq_cputime;
>  
+	lockdep_assert_irqs_disabled();

> -	local_irq_save(flags);
>  	irq_cputime = nsecs_to_cputime64(__this_cpu_read(cpu_hardirq_time)) -
>  		      cpustat[CPUTIME_IRQ];
>  	irq_cputime = min(irq_cputime, maxtime);
>  	cpustat[CPUTIME_IRQ] += irq_cputime;
> -	local_irq_restore(flags);
> +
>  	return irq_cputime;
>  }
>  
>  static cputime_t irqtime_account_si_update(cputime_t maxtime)
>  {
>  	u64 *cpustat = kcpustat_this_cpu->cpustat;
> -	unsigned long flags;
>  	cputime_t softirq_cputime;
>  
+	lockdep_assert_irqs_disabled();

> -	local_irq_save(flags);
>  	softirq_cputime = nsecs_to_cputime64(__this_cpu_read(cpu_softirq_time)) -
>  			  cpustat[CPUTIME_SOFTIRQ];
>  	softirq_cputime = min(softirq_cputime, maxtime);
>  	cpustat[CPUTIME_SOFTIRQ] += softirq_cputime;
> -	local_irq_restore(flags);
> +
>  	return softirq_cputime;
>  }

---
Subject: locking/lockdep: Provide IRQ state assertion helpers

Provide a cheap alternative to:

	WARN_ON(!irqs_disabled());

This patch provides:

	lockdep_assert_irqs_disabled();
	lockdep_assert_softirqs_disabled();

Which compile away for CONFIG_LOCKDEP=n kernels.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -526,6 +526,23 @@ static inline void print_irqtrace_events
 }
 #endif
 
+#if defined(CONFIG_LOCKDEP) && defined(CONFIG_TRACE_IRQFLAGS)
+
+#define lockdep_assert_irqs_disabled() do {				\
+		WARN_ON(debug_locks && current->hardirqs_enabled);	\
+	} while (0)
+
+#define lockdep_assert_softirqs_disabled() do {				\
+		WARN_ON(debug_locks && current->softirqs_enabled);	\
+	} while (0)
+
+#else
+
+#define lockdep_assert_irqs_disabled()		do { } while (0)
+#define lockdep_assert_softirqs_disabled()	do { } while (0)
+
+#endif
+
 /*
  * For trivial one-depth nesting of a lock-class, the following
  * global define can be used. (Subsystems with multiple levels