linux-kernel - Re: [Query]: sched/fair: prio_changed

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Message-ID: <509A1438.7020008@linux.vnet.ibm.com>
Date:	Wed, 07 Nov 2012 15:56:40 +0800
From:	Michael Wang <wangyun@...ux.vnet.ibm.com>
To:	Viresh Kumar <viresh.kumar@...aro.org>
CC:	mingo@...hat.com, Peter Zijlstra <peterz@...radead.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Lists linaro-dev <linaro-dev@...ts.linaro.org>,
	PDSW-power-team <pdsw-power-team@....com>
Subject: Re: [Query]: sched/fair: prio_changed_fair()

On 11/07/2012 03:49 PM, Viresh Kumar wrote:
Hi, Viresh
> Hi Ingo/Peter,
> 
> I am trying to understand the complex scheduler code and just found
> something incorrect (maybe i am not reading it well):
> 
> File: kernel/sched/fair.c
> 
> static void
> prio_changed_fair(struct rq *rq, struct task_struct *p, int oldprio)
> {
> 	if (!p->se.on_rq)
> 		return;
> 
> 	/*
> 	 * Reschedule if we are currently running on this runqueue and
> 	 * our priority decreased, or if we are not currently running on
> 	 * this runqueue and our priority is higher than the current's
> 	 */
> 	if (rq->curr == p) {
> 		if (p->prio > oldprio)
> 			resched_task(rq->curr);
> 	} else
> 		check_preempt_curr(rq, p, 0);
> }
> 
> 
> Comment says that we must mark the task to be rescheduled, if we
> are currently running and our priority has decreased. But in code we
> are checking (p->prio > oldprio). i.e. reschedule if we were currently
> running and our priority increased.

It's the user nice value I suppose, so it should be reversed when we are
talking about weight.

Regards,
Michael Wang

> 
> Sorry if i am wrong :(
> 
> --
> viresh
> --
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