linux-kernel - Re: [PATCH v2] kvm: remove dependence on delay-accounting

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Date:	Mon, 16 Jan 2012 17:42:58 +0400
From:	Konstantin Khlebnikov <khlebnikov@...nvz.org>
To:	Marcelo Tosatti <mtosatti@...hat.com>
CC:	Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...e.hu>,
	Avi Kivity <avi@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>
Subject: Re: [PATCH v2] kvm: remove dependence on delay-accounting

Marcelo Tosatti wrote:
> On Sat, Jan 14, 2012 at 08:30:51PM +0400, Konstantin Khlebnikov wrote:
>> KVM selects delay-accounting only to get sched-info for steal-time accounting.
>> Meanwhile delay-accounting can be disabled by boot option. This is ridiculous.
>>
>> This patch adds internal boolean option CONFIG_TASK_SCHED_INFO to enable only
>> task->sched_info and its collecting inside scheduler.
>>

<cut>

>>   static inline int sched_info_on(void)
>>   {
>> -#ifdef CONFIG_SCHEDSTATS
>> +#if IS_ENABLED(CONFIG_SCHEDSTATS) || IS_ENABLED(CONFIG_KVM)
>>   	return 1;
>
> CONFIG_TASK_SCHED_INFO?
>

It makes it equal to constant 1, because all its callers are
under #ifdef CONFIG_TASK_SCHED_INFO =)

its current code:

static inline int sched_info_on(void)
{
#ifdef CONFIG_SCHEDSTATS
	return 1;
#elif defined(CONFIG_TASK_DELAY_ACCT)
	extern int delayacct_on;
	return delayacct_on;
#else
	return 0;
#endif
}

CONFIG_SCHEDSTATS == debug option in lib/Kconfig.debug for /proc/schedstat
CONFIG_TASK_DELAY_ACCT == wierd net-link based statistics collecting tool

Thus, may be better to remove this function, because it can return 0
only if delay-accounting is compiled but disabled by boot option
(delayacct_on =1 by default since 2.6.18)

patch follows...

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