linux-kernel - Re: [patch] CFS scheduler, -v14

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Message-ID: <46555886.4040408@linux.vnet.ibm.com>
Date:	Thu, 24 May 2007 14:49:02 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mike Galbraith <efault@....de>,
	Arjan van de Ven <arjan@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	pranith-kumar_d@...torg.com, Andi Kleen <andi@...stfloor.org>
Subject: Re: [patch] CFS scheduler, -v14

Ingo Molnar wrote:
> btw., i think some more consolidation could be done in this area. We've 
> now got the traditional /proc/PID/stat metrics, schedstats, taskstats 
> and delay accounting and with CFS we've got /proc/sched_debug and 
> /proc/PID/sched. There's a fair amount of overlap.
> 

Yes. true. schedstats and delay accounting share code and taskstats is
a transport mechansim. I'll try and look at /proc/PID/stat and /proc/PID/sched
and /proc/sched_debug.

> btw., CFS does this change to fs/proc/array.c:
> 
> @@ -410,6 +408,14 @@ static int do_task_stat(struct task_stru
>  	/* convert nsec -> ticks */
>  	start_time = nsec_to_clock_t(start_time);
> 
> +	/*
> +	 * Use CFS's precise accounting, if available:
> +	 */
> +	if (!has_rt_policy(task)) {
> +		utime = nsec_to_clock_t(task->sum_exec_runtime);
> +		stime = 0;
> +	}
> +
>  	res = sprintf(buffer,"%d (%s) %c %d %d %d %d %d %lu %lu \
>  %lu %lu %lu %lu %lu %ld %ld %ld %ld %d 0 %llu %lu %ld %lu %lu %lu %lu %lu \
>  %lu %lu %lu %lu %lu %lu %lu %lu %d %d %lu %lu %llu\n",
> 
> if you have some spare capacity to improve this code, it could be 
> further enhanced by not setting 'stime' to zero, but using the existing 
> jiffies based utime/stime statistics as a _ratio_ to split up the 
> precise p->sum_exec_runtime. That way we dont have to add precise 
> accounting to syscall entry/exit points (that would be quite expensive), 
> but still the sum of utime+stime would be very precise. (and that's what 
> matters most anyway)
> 
> 	Ingo

I'll start looking into splitting sum_exec_time into utime and stime
based on the ratio already present in the task structure. 

-- 
	Warm Regards,
	Balbir Singh
	Linux Technology Center
	IBM, ISTL
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