linux-kernel - Re: [PATCH] sched: fix cpu utilization account error

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Message-ID: <51D24708.1060206@linux.vnet.ibm.com>
Date:	Tue, 02 Jul 2013 11:20:40 +0800
From:	Michael Wang <wangyun@...ux.vnet.ibm.com>
To:	Xie XiuQi <xiexiuqi@...wei.com>
CC:	Mike Galbraith <efault@....de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	stable@...r.kernel.org, Li Zefan <lizefan@...wei.com>,
	Zhang Hang <bob.zhanghang@...wei.com>,
	Li Bin <huawei.libin@...wei.com>
Subject: Re: [PATCH] sched: fix cpu utilization account error

Hi, Xie

On 07/01/2013 07:26 PM, Xie XiuQi wrote:
[snip]
> Here is the kthread main logic. Although it's not a good idea, but it does
> exist:
> while (!kthread_should_stop()) {
> 	/* call schedule every 1 sec */
> 	if (HZ <= jiffies - last) {
> 		last = jiffies;
> 		schedule();
> 	}
> 
> 	/* get data and sent it */
> 	get_msg();
> 	send_msg();

What about use cond_resched() here? Isn't that more gentle?

Regards,
Michael Wang

> 
> 	if (kthread_should_stop())
> 		break;
> }
> 
>> That said, accounting funnies induced by skipped update are possible,
>> which could trump the cycle savings I suppose, so maybe savings (sniff)
>> should just go away?
> 
> Indeed, removing the skip_clock_update could resolve the issue, but I found
> there is no this issue in preempt mode. However, if remove skip_clock_update
> we'll get more precise time account.
> 
> So, what's your opinion, Mike.
> 
> 
> 
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