linux-kernel - Re: [RFC] Extend mwait idle to optimize away IPIs when possible

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Date:	Mon, 06 Feb 2012 17:24:21 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	David Daney <david.daney@...ium.com>
CC:	Venkatesh Pallipadi <venki@...gle.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Aaron Durbin <adurbin@...gle.com>,
	Paul Turner <pjt@...gle.com>, linux-kernel@...r.kernel.org
Subject: Re: [RFC] Extend mwait idle to optimize away IPIs when possible

On 02/06/2012 04:26 PM, David Daney wrote:
> On 02/06/2012 12:42 PM, Venkatesh Pallipadi wrote:
> [...]
>> index 5bed94e..6a56cb0 100644
>> --- a/arch/x86/Kconfig
>> +++ b/arch/x86/Kconfig
>> @@ -170,6 +170,11 @@ config GENERIC_TIME_VSYSCALL
>>       bool
>>       default X86_64
>>
>> +config AVOID_IPI_ON_IDLE
>> +    bool
>> +    depends on X86_64
>> +    default X86_64
>> +
> 
> Can you get rid of this part...
> 
>>   config ARCH_HAS_CPU_RELAX
>>       def_bool y
>>
> [...]
>> diff --git a/arch/x86/kernel/acpi/cstate.c
>> b/arch/x86/kernel/acpi/cstate.c
>> index f50e7fb..340c4e9 100644
>> --- a/arch/x86/kernel/acpi/cstate.c
>> +++ b/arch/x86/kernel/acpi/cstate.c
>> @@ -161,6 +161,14 @@ EXPORT_SYMBOL_GPL(acpi_processor_ffh_cstate_probe);
>>    */
>>   void mwait_idle_with_hints(unsigned long ax, unsigned long cx)
>>   {
>> +#ifdef CONFIG_AVOID_IPI_ON_IDLE
> 
> 
> ... and change all of these to #ifdef CONFIG_64BIT
> 
>> +    int oldval, cpu = smp_processor_id();
>> +

Why should this be 64-bit specific??

	-hpa


-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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