linux-kernel - Re: [PATCH] x86: apic: disarm apic timer in deadline mode when shut down clockevent

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Message-ID: <20140416074027.GB5636@gmail.com>
Date:	Wed, 16 Apr 2014 09:40:27 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	"Wang, Biao" <biao.wang@...el.com>
Cc:	"hpa@...or.com" <hpa@...or.com>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Zhang, Di" <di.zhang@...el.com>
Subject: Re: [PATCH] x86: apic: disarm apic timer in deadline mode when shut
 down clockevent


* Wang, Biao <biao.wang@...el.com> wrote:

> For tsc deadline mode, when we shut down clockevent we should disarm
> local-APIC timer like count-down mode.
> 
> Signed-off-by: wang, biao <biao.wang@...el.com>
> Signed-off-by: Zhang Di <di.zhang@...el.com>
> ---
>  arch/x86/kernel/apic/apic.c |    4 ++++
>  1 files changed, 4 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
> index 7f26c9a..85889ba 100644
> --- a/arch/x86/kernel/apic/apic.c
> +++ b/arch/x86/kernel/apic/apic.c
> @@ -512,6 +512,10 @@ static void lapic_timer_setup(enum clock_event_mode mode,
>  		v |= (APIC_LVT_MASKED | LOCAL_TIMER_VECTOR);
>  		apic_write(APIC_LVTT, v);
>  		apic_write(APIC_TMICT, 0);
> +
> +		/*disarm timer in deadline mode*/
> +		if (boot_cpu_has(X86_FEATURE_TSC_DEADLINE_TIMER))
> +			wrmsrl(MSR_IA32_TSC_DEADLINE, 0);
>  		break;

Please fix the changelog to conform to the standard changelog style:

 - first describe the symptoms of the bug - how does a user notice?

 - then describe how the code behaves today and how that is causing the bug

 - and then only describe how it's fixed.

The first item is the most important one - while developers 
(naturally) tend to concentrate on the least important point,
the last one.

Thanks,

        Ingo
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