linux-kernel - Re: [PATCH 1/2] Add another clock for use with the soft lockup watchdog.

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Date:	Mon, 5 Jan 2015 14:09:59 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Cyril Bur <cyrilbur@...il.com>
Cc:	linux-kernel@...r.kernel.org, mpe@...erman.id.au,
	drjones@...hat.com, dzickus@...hat.com, mingo@...nel.org,
	uobergfe@...hat.com, chaiw.fnst@...fujitsu.com, cl@...u.com,
	fabf@...net.be, atomlin@...hat.com, benzh@...omium.org
Subject: Re: [PATCH 1/2] Add another clock for use with the soft lockup
 watchdog.

On Mon, 22 Dec 2014 16:06:03 +1100 Cyril Bur <cyrilbur@...il.com> wrote:

> This permits the use of arch specific clocks for which virtualised kernels can
> use their notion of 'running' time, not the elpased wall time which will
> include host execution time.
> 
> ...
>
> --- a/kernel/sched/clock.c
> +++ b/kernel/sched/clock.c
> @@ -74,6 +74,20 @@ unsigned long long __weak sched_clock(void)
>  }
>  EXPORT_SYMBOL_GPL(sched_clock);
>  
> +/*
> + * Running clock - returns the time that has elapsed while a guest has been
> + * running.
> + * On a guest this value should be sched_clock minus the time the
> + * guest was suspended by the hypervisor (for any reason).
> + * On bare metal this function should return the same as sched_clock.
> + * Architectures and sub-architectures can override this.
> + */
> +unsigned long long __weak running_clock(void)
> +{
> +	return sched_clock();
> +}
> +EXPORT_SYMBOL_GPL(running_clock);

Exporting a weak symbol seems a bit strange, but I guess it will work. 
However nothing *uses* this export and it seems unlikely to me that
anything will do so.

So I'm inclined to zap it, OK?

--- a/kernel/sched/clock.c~add-another-clock-for-use-with-the-soft-lockup-watchdog-fix
+++ a/kernel/sched/clock.c
@@ -86,7 +86,6 @@ unsigned long long __weak running_clock(
 {
 	return sched_clock();
 }
-EXPORT_SYMBOL_GPL(running_clock);
 
 __read_mostly int sched_clock_running;
 
_

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