linux-kernel - Re: [RFC PATCH v1 15/31] ARC: Process/scheduling/clock/Timers/Delay Management

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Message-ID: <CAFTL4hz95LF0qetu+tjR3ZyHf0PWKwc40Sx-puJaUdrsSXgvKw@mail.gmail.com>
Date:	Fri, 4 Jan 2013 14:01:42 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Vineet Gupta <Vineet.Gupta1@...opsys.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>, linux-arch@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v1 15/31] ARC: Process/scheduling/clock/Timers/Delay Management

2013/1/2 Vineet Gupta <Vineet.Gupta1@...opsys.com>:
> On Tuesday 13 November 2012 01:59 AM, Thomas Gleixner wrote:
>> On Wed, 7 Nov 2012, Vineet Gupta wrote:
>>> +void cpu_idle(void)
>>> +{
>>> +    /* Since we SLEEP in idle loop, TIF_POLLING_NRFLAG can't be set */
>>> +
>>> +    /* endless idle loop with no priority at all */
>>> +    while (1) {
>>> +            tick_nohz_idle_enter();
>>> +
>>> +            while (!need_resched())
>>> +                    arch_idle();
>>> +
>>> +            tick_nohz_idle_exit();
>>> +
>>> +            preempt_enable_no_resched();
>>> +            schedule();
>>> +            preempt_disable();
>>
>>               schedule_preempt_disabled() please
>
>
> OK ! And it seems I was also missing the calls to rcu_idle_enter()/exit() to track
> commit 1268fbc746ea  "nohz: Remove tick_nohz_idle_enter_norcu() / ..."

Right!

They must be placed around the code that sets the low power mode, when
you know there is no use of RCU between rcu_idle_enter() /
rcu_idle_exit(). Here this would be likely:

while (1) {
        tick_nohz_idle_enter();

+      rcu_idle_enter();
        while (!need_resched())
                arch_idle();
+      rcu_idle_exit()

        tick_nohz_idle_exit();
        schedule_preempt_disabled();
}
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