linux-kernel - Re: [PATCH 18/25] hrtimer: Enable soft and hard hrtimer

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Date:   Wed, 27 Sep 2017 16:18:25 +0200 (CEST)
From:   Anna-Maria Gleixner <anna-maria@...utronix.de>
To:     Peter Zijlstra <peterz@...radead.org>
cc:     LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Christoph Hellwig <hch@....org>, keescook@...omium.org,
        John Stultz <john.stultz@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 18/25] hrtimer: Enable soft and hard hrtimer

On Tue, 26 Sep 2017, Peter Zijlstra wrote:

> On Thu, Aug 31, 2017 at 12:23:42PM -0000, Anna-Maria Gleixner wrote:
> > --- a/include/linux/hrtimer.h
> > +++ b/include/linux/hrtimer.h
> > @@ -23,6 +23,17 @@
> >  #include <linux/timer.h>
> >  #include <linux/timerqueue.h>
> >  
> > +/*
> > + * Clock ids for hrtimers which expire in softirq context. These clock ids
> > + * are kernel internal and never exported to user space.
> > + */
> > +#define HRTIMER_BASE_SOFT_MASK	MAX_CLOCKS
> > +
> > +#define CLOCK_REALTIME_SOFT	(CLOCK_REALTIME	 | HRTIMER_BASE_SOFT_MASK)
> > +#define CLOCK_MONOTONIC_SOFT	(CLOCK_MONOTONIC | HRTIMER_BASE_SOFT_MASK)
> > +#define CLOCK_BOOTTIME_SOFT	(CLOCK_BOOTTIME	 | HRTIMER_BASE_SOFT_MASK)
> > +#define CLOCK_TAI_SOFT		(CLOCK_TAI	 | HRTIMER_BASE_SOFT_MASK)
> > +
> >  struct hrtimer_clock_base;
> >  struct hrtimer_cpu_base;
> >  
> 
> > --- a/kernel/time/hrtimer.c
> > +++ b/kernel/time/hrtimer.c
> > @@ -1173,7 +1161,7 @@ u64 hrtimer_get_next_event(void)
> >  
> >  static inline int hrtimer_clockid_to_base(clockid_t clock_id)
> >  {
> > +	if (likely(clock_id < MAX_CLOCKS_HRT)) {
> >  		int base = hrtimer_clock_to_base_table[clock_id];
> >  
> >  		if (likely(base != HRTIMER_MAX_CLOCK_BASES))
> > @@ -1193,8 +1181,12 @@ static void __hrtimer_init(struct hrtime
> >  
> >  	cpu_base = raw_cpu_ptr(&hrtimer_bases);
> >  
> > +	if (mode != HRTIMER_MODE_ABS) {
> > +		if (clock_id == CLOCK_REALTIME)
> > +			clock_id = CLOCK_MONOTONIC;
> > +		else if (clock_id == CLOCK_REALTIME_SOFT)
> > +			clock_id = CLOCK_MONOTONIC_SOFT;
> > +	}
> >  
> >  	base = hrtimer_clockid_to_base(clock_id);
> >  	timer->base = &cpu_base->clock_base[base];
> 
> So why expose these extra bases at all, why not stick another flag in
> MODE? These extra bases is a pure implementation detail imo; you could
> equally implement the functionality without (albeit at extra cost).
> 

It was Thomas' request not to use a flag for this.

Anna-Maria