linux-kernel - Re: [PATCH 2/2] x86/apic: check global clockevent in lapic timer setup

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Date:	Thu, 17 Dec 2009 14:34:24 -0800
From:	"H. Peter Anvin" <hpa@...ux.intel.com>
To:	"Pan, Jacob jun" <jacob.jun.pan@...el.com>
CC:	Cyrill Gorcunov <gorcunov@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"x86@...nel.org" <x86@...nel.org>
Subject: Re: [PATCH 2/2] x86/apic: check global clockevent in lapic timer
 setup

On 12/17/2009 02:31 PM, Pan, Jacob jun wrote:
>> Wouldn't be better to operate the same way as in case of "noapictimer"
>> boot option. I guess the non-pc x86 midplatforms you're mentioning
>> do not use SMP ever but just to be consistent in code.
>>
> [[JPAN]] We do use SMP with hyper threading in Moorestown.
> In that case we have a per cpu platform timer without global clockevent.
> so i think we don't want the dummy lapic event. we don't want to use the
> broadcast mechanism as mentioned in the comments before disabling lapic
> timer.
> 
> For moorestown, I can use x86_init.timers.setup_percpu_clockev
> abstraction function so that Moorestown platform does not need to call
> setup_boot_APIC_clock() if per cpu platform timer is used. so many IFs :).
> 
> But in the case of having constant and always on LAPIC timer, we still do
> not want the dummy lapic clockevent and the broadcast. we will just have
> per cpu always on local apic timers without global clockevent device.

OK, I'm not entirely sure I follow this, and I'm not sure someone trying
to understand the code in five years would, either.  I don't really see
the above translating into "we don't have a global clockevent, therefore
we shouldn't initialize (but should still not disable) the local APIC
timer."

	-hpa
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