linux-kernel - Re: [patch 02/14] remove clocksource inline functions

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Date:	Fri, 14 Aug 2009 10:17:01 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Martin Schwidefsky <schwidefsky@...ibm.com>
cc:	john stultz <johnstul@...ibm.com>, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...e.hu>, Daniel Walker <dwalker@...o99.com>
Subject: Re: [patch 02/14] remove clocksource inline functions

On Fri, 14 Aug 2009, Martin Schwidefsky wrote:
> On Thu, 13 Aug 2009 15:14:34 -0700
> john stultz <johnstul@...ibm.com> wrote:
> > So you'll need to preserve the cycle_last = 0 line.
> 
> Whoa, now that is subtle. Good spotting. I would prefer to reset the 
> cycle_last in a resume function though:
> 
> Index: linux-2.6/arch/x86/kernel/tsc.c
> ===================================================================
> --- linux-2.6.orig/arch/x86/kernel/tsc.c
> +++ linux-2.6/arch/x86/kernel/tsc.c
> @@ -744,10 +744,16 @@ static cycle_t __vsyscall_fn vread_tsc(v
>  }
>  #endif
> 
> +static void resume_tsc(void)
> +{
> +       clocksource_tsc.cycle_last = 0;
> +}
> +
>  static struct clocksource clocksource_tsc = {
>         .name                   = "tsc",
>         .rating                 = 300,
>         .read                   = read_tsc,
> +       .resume                 = resume_tsc,
>         .mask                   = CLOCKSOURCE_MASK(64),
>         .shift                  = 22,
>         .flags                  = CLOCK_SOURCE_IS_CONTINUOUS |
> 
> That puts the subtlety where it belongs.

Ack.

	tglx
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