RE: [PATCH] sched: fix interactive ceiling code

[tim_c_chen@linux.intel.com]

The patch did recover the 4% regression for Volanomark which started the
whole thread in the first place.

Tim

> Con Kolivas wrote on Thursday, May 18, 2006 6:31 PM
>> Ingo, Andrew, I think these are minor logic fixes and comments that
>> correct
>> a patch that has already been pushed to 2.6.17- and I would like them
>> short
>> circuited to mainline if everyone is comfortable with it.
>>
>> Ken, Mike can I ask you to put a signed off on this patch for your
>> contributions please?
>
> Yup, looks good. Thanks for all the explanation and certainly your
> patience.
>
> Signed-off-by: Ken Chen <kenneth.w.chen@intel.com>
>
>
>
>> ---
>> The relationship between INTERACTIVE_SLEEP and the ceiling is not
>> perfect
>> and not explicit enough. The sleep boost is not supposed to be any
>> larger
>> than without this code and the comment is not clear enough about what
>> exactly
>> it does, just the reason it does it. Fix it.
>>
>> There is a ceiling to the priority beyond which tasks that only ever
>> sleep
>> for very long periods cannot surpass. Fix it.
>>
>> Prevent the on-runqueue bonus logic from defeating the idle sleep logic.
>>
>> Opportunity to micro-optimise.
>>
>> Signed-off-by: Con Kolivas <kernel@kolivas.org>
>>
>> ---
>>  kernel/sched.c |   52
>> +++++++++++++++++++++++++++-------------------------
>>  1 files changed, 27 insertions(+), 25 deletions(-)
>>
>> Index: linux-2.6.17-rc4/kernel/sched.c
>> ===================================================================
>> --- linux-2.6.17-rc4.orig/kernel/sched.c	2006-05-19 11:25:01.000000000
>> +1000
>> +++ linux-2.6.17-rc4/kernel/sched.c	2006-05-19 11:25:14.000000000 +1000
>> @@ -731,33 +731,35 @@ static inline void __activate_idle_task(
>>  static int recalc_task_prio(task_t *p, unsigned long long now)
>>  {
>>  	/* Caller must always ensure 'now >= p->timestamp' */
>> -	unsigned long long __sleep_time = now - p->timestamp;
>> -	unsigned long sleep_time;
>> +	unsigned long sleep_time = now - p->timestamp;
>>
>>  	if (batch_task(p))
>>  		sleep_time = 0;
>> -	else {
>> -		if (__sleep_time > NS_MAX_SLEEP_AVG)
>> -			sleep_time = NS_MAX_SLEEP_AVG;
>> -		else
>> -			sleep_time = (unsigned long)__sleep_time;
>> -	}
>>
>>  	if (likely(sleep_time > 0)) {
>>  		/*
>> -		 * User tasks that sleep a long time are categorised as
>> -		 * idle. They will only have their sleep_avg increased to a
>> -		 * level that makes them just interactive priority to stay
>> -		 * active yet prevent them suddenly becoming cpu hogs and
>> -		 * starving other processes.
>> +		 * This ceiling is set to the lowest priority that would allow
>> +		 * a task to be reinserted into the active array on timeslice
>> +		 * completion.
>>  		 */
>> -		if (p->mm && sleep_time > INTERACTIVE_SLEEP(p)) {
>> -				unsigned long ceiling;
>> +		unsigned long ceiling = INTERACTIVE_SLEEP(p);
>>
>> -				ceiling = JIFFIES_TO_NS(MAX_SLEEP_AVG -
>> -					DEF_TIMESLICE);
>> -				if (p->sleep_avg < ceiling)
>> -					p->sleep_avg = ceiling;
>> +		if (p->mm && sleep_time > ceiling && p->sleep_avg < ceiling) {
>> +			/*
>> +			 * Prevents user tasks from achieving best priority
>> +			 * with one single large enough sleep.
>> +			 */
>> +			p->sleep_avg = ceiling;
>> +			/*
>> +			 * Using INTERACTIVE_SLEEP() as a ceiling places a
>> +			 * nice(0) task 1ms sleep away from promotion, and
>> +			 * gives it 700ms to round-robin with no chance of
>> +			 * being demoted.  This is more than generous, so
>> +			 * mark this sleep as non-interactive to prevent the
>> +			 * on-runqueue bonus logic from intervening should
>> +			 * this task not receive cpu immediately.
>> +			 */
>> +			p->sleep_type = SLEEP_NONINTERACTIVE;
>>  		} else {
>>  			/*
>>  			 * Tasks waking from uninterruptible sleep are
>> @@ -765,12 +767,12 @@ static int recalc_task_prio(task_t *p, u
>>  			 * are likely to be waiting on I/O
>>  			 */
>>  			if (p->sleep_type == SLEEP_NONINTERACTIVE && p->mm) {
>> -				if (p->sleep_avg >= INTERACTIVE_SLEEP(p))
>> +				if (p->sleep_avg >= ceiling)
>>  					sleep_time = 0;
>>  				else if (p->sleep_avg + sleep_time >=
>> -						INTERACTIVE_SLEEP(p)) {
>> -					p->sleep_avg = INTERACTIVE_SLEEP(p);
>> -					sleep_time = 0;
>> +					 ceiling) {
>> +						p->sleep_avg = ceiling;
>> +						sleep_time = 0;
>>  				}
>>  			}
>>
>> @@ -784,9 +786,9 @@ static int recalc_task_prio(task_t *p, u
>>  			 */
>>  			p->sleep_avg += sleep_time;
>>
>> -			if (p->sleep_avg > NS_MAX_SLEEP_AVG)
>> -				p->sleep_avg = NS_MAX_SLEEP_AVG;
>>  		}
>> +		if (p->sleep_avg > NS_MAX_SLEEP_AVG)
>> +			p->sleep_avg = NS_MAX_SLEEP_AVG;
>>  	}
>>
>>  	return effective_prio(p);
>> --
>> -ck
>