linux-kernel - RE: + restore-missing-sysfs-max_cstate-attr.patch added to -mm tree

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Date:	Fri, 4 Jan 2008 13:59:01 -0800
From:	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>
To:	"Mark Lord" <lkml@....ca>
Cc:	"Arjan van de Ven" <arjan@...radead.org>,
	"Andrew Morton" <akpm@...ux-foundation.org>, <abelay@...ell.com>,
	<lenb@...nel.org>, "Ingo Molnar" <mingo@...e.hu>,
	<linux-kernel@...r.kernel.org>, <linux-acpi@...r.kernel.org>,
	<rjw@...k.pl>
Subject: RE: + restore-missing-sysfs-max_cstate-attr.patch added to -mm tree


>-----Original Message-----
>From: Mark Lord [mailto:lkml@....ca] 
>Sent: Friday, January 04, 2008 1:53 PM
>To: Pallipadi, Venkatesh
>Cc: Arjan van de Ven; Andrew Morton; abelay@...ell.com; 
>lenb@...nel.org; Ingo Molnar; linux-kernel@...r.kernel.org; 
>linux-acpi@...r.kernel.org; rjw@...k.pl
>Subject: Re: + restore-missing-sysfs-max_cstate-attr.patch 
>added to -mm tree
>
>Mark Lord wrote:
>> Venki Pallipadi wrote:
>>> Reintroduce run time configurable max_cstate for !CPU_IDLE case.
>>>
>>> Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>
>>>
>>> Index: linux-2.6.24-rc/drivers/acpi/processor_idle.c
>>> ===================================================================
>>> --- linux-2.6.24-rc.orig/drivers/acpi/processor_idle.c
>>> +++ linux-2.6.24-rc/drivers/acpi/processor_idle.c
>>> @@ -76,7 +76,11 @@ static void (*pm_idle_save) (void) __rea
>>>  #define PM_TIMER_TICKS_TO_US(p)        (((p) * 
>>> 1000)/(PM_TIMER_FREQUENCY/1000))
>>>  
>>>  static unsigned int max_cstate __read_mostly = 
>ACPI_PROCESSOR_MAX_POWER;
>>> +#ifdef CONFIG_CPU_IDLE
>>>  module_param(max_cstate, uint, 0000);
>>> +#else
>>> +module_param(max_cstate, uint, 0644);
>>> +#endif
>>>  static unsigned int nocst __read_mostly;
>>>  module_param(nocst, uint, 0000);
>>>  
>> ..
>> 
>> I'll try and re-test with this on Friday.
>..
>
>Okay, with !CONFIG_CPU_IDLE, this works fine -- same as 2.6.23 
>and earlier.
>

Good to know. Atleast we do not have a regression for 2.6.24 now.

>> Meanwhile, can you give a short summary of how behaviour differs
>> between CONFIG_CPU_IDLE and !CONFIG_CPU_IDLE  ??
>> 
>> I'm not at all clear on how this really affects things.
>

With CPU_IDLE, the C-state policy is removed from acpi driver. Ideally
policy should have nothing to do with ACPI, as ACPI only provides the
C-state mechanisms. So, with CPU_IDLE, it is not easy to control this
variable through a acpi driver module at run time. Also, the latency
interface that was mentioned before is to serve the same purpose in a
more clear manner (based on the wakeup latency) instead of a C-state
number which may not mean much from the end user point of view.

I will look at why latency does not work on a single core system
soon(Was that with UP kernel or SMP kernel?). That way we will have a
proper cover for this with CPU_IDLE in future.

Thanks,
Venki
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