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

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Message-ID: <20130821182646.GU239280@redhat.com>
Date:	Wed, 21 Aug 2013 14:26:46 -0400
From:	Don Zickus <dzickus@...hat.com>
To:	Frederic Weisbecker <fweisbec@...il.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 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.

Cheers,
Don
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