linux-kernel - Re: [RFC PATCH 2/6] x86: nsecs to cycles conversion

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Message-ID: <20130830103528.GA7806@somewhere>
Date:	Fri, 30 Aug 2013 12:35:29 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Don Zickus <dzickus@...hat.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	John Stultz <john.stultz@...aro.org>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [RFC PATCH 2/6] x86: nsecs to cycles conversion

On Wed, Aug 21, 2013 at 02:26:46PM -0400, Don Zickus wrote:
> On Wed, Aug 21, 2013 at 06:42:17PM +0200, Frederic Weisbecker wrote:
> > hw_nmi_get_sample_period() is simply a conversion from a period
> > to cycles. Lets generalize the API naming so that it can be used for
> > wider purpose than just watchdog perf event settings. Also it makes the
> > function name less opaque about what it really does.
> > 
> 
> <snip>
> 
> > diff --git a/arch/x86/include/asm/cycles.h b/arch/x86/include/asm/cycles.h
> > new file mode 100644
> > index 0000000..7dedeb3
> > --- /dev/null
> > +++ b/arch/x86/include/asm/cycles.h
> > @@ -0,0 +1,11 @@
> > +#ifndef _ASM_X86_CYCLES_H
> > +#define _ASM_X86_CYCLES_H
> > +
> > +#include <linux/time.h>
> > +#include <asm/tsc.h>
> > +
> > +static inline u64 nsecs_to_cycles(u64 nsecs)
> > +{
> > +	return (u64)((cpu_khz) * nsecs) / NSEC_PER_MSEC;
> > +}
> > +#endif /* #ifndef _ASM_X86_CYCLES_H */
> > diff --git a/arch/x86/kernel/apic/hw_nmi.c b/arch/x86/kernel/apic/hw_nmi.c
> > index a698d71..4015906 100644
> > --- a/arch/x86/kernel/apic/hw_nmi.c
> > +++ b/arch/x86/kernel/apic/hw_nmi.c
> > @@ -19,13 +19,6 @@
> >  #include <linux/module.h>
> >  #include <linux/delay.h>
> >  
> > -#ifdef CONFIG_HARDLOCKUP_DETECTOR
> > -u64 hw_nmi_get_sample_period(int watchdog_thresh)
> > -{
> > -	return (u64)(cpu_khz) * 1000 * watchdog_thresh;
> > -}
> > -#endif
> > -
> >  #ifdef arch_trigger_all_cpu_backtrace
> >  /* For reliability, we're prepared to waste bits here. */
> >  static DECLARE_BITMAP(backtrace_mask, NR_CPUS) __read_mostly;
> > diff --git a/kernel/watchdog.c b/kernel/watchdog.c
> > index 1241d8c..e04887c 100644
> > --- a/kernel/watchdog.c
> > +++ b/kernel/watchdog.c
> > @@ -26,6 +26,7 @@
> >  #include <linux/sched/rt.h>
> >  
> >  #include <asm/irq_regs.h>
> > +#include <asm/cycles.h>
> >  #include <linux/kvm_para.h>
> >  #include <linux/perf_event.h>
> 
> Do you have to wrap the above with #ifdef CONFIG_HARDLOCKUP_DETECTOR?
> Otherwise non-x86 boxes won't compile unless I missed stub
> nsecs_to_cycles() somewhere.

Good catch, I forgot that.

Thanks.

> 
> Cheers,
> Don
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