linux-kernel - Re: [PATCH 17/25] hrtimer: Implementation of softirq hrtimer handling

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Message-ID: <20170928081501.pmleqw3gr6cftgrx@hirez.programming.kicks-ass.net>
Date:   Thu, 28 Sep 2017 10:15:01 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Anna-Maria Gleixner <anna-maria@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Christoph Hellwig <hch@....org>, keescook@...omium.org,
        John Stultz <john.stultz@...aro.org>
Subject: Re: [PATCH 17/25] hrtimer: Implementation of softirq hrtimer handling

On Thu, Sep 28, 2017 at 09:59:50AM +0200, Thomas Gleixner wrote:
> On Wed, 27 Sep 2017, Peter Zijlstra wrote:
> > On Thu, Aug 31, 2017 at 12:23:42PM -0000, Anna-Maria Gleixner wrote:
> >  static void __run_hrtimer(struct hrtimer_cpu_base *cpu_base,
> >  			  struct hrtimer_clock_base *base,
> >  			  struct hrtimer *timer, ktime_t *now,
> > -			  bool hardirq)
> > +			  unsigned long flags)
> >  {
> >  	enum hrtimer_restart (*fn)(struct hrtimer *);
> >  	int restart;
> > @@ -1298,19 +1323,13 @@ static void __run_hrtimer(struct hrtimer
> >  	 * protected against migration to a different CPU even if the lock
> >  	 * is dropped.
> >  	 */
> > -	if (hardirq)
> > -		raw_spin_unlock(&cpu_base->lock);
> > -	else
> > -		raw_spin_unlock_irq(&cpu_base->lock);
> > +	raw_spin_unlock_irqrestore(&cpu_base->lock, flags);
> >  
> >  	trace_hrtimer_expire_entry(timer, now);
> >  	restart = fn(timer);
> >  	trace_hrtimer_expire_exit(timer);
> >  
> > -	if (hardirq)
> > -		raw_spin_lock(&cpu_base->lock);
> > -	else
> > -		raw_spin_lock_irq(&cpu_base->lock);
> > +	raw_spin_lock_irqsave(&cpu_base->lock, flags);
> 
> No point in irqsave() here. _irq() is sufficient as we leave the function
> right after that.

True, I wasn't entirely sure on the irq tracing assumptions (if any) and
was too lazy to double check.