linux-kernel - Re: [PATCH] timer: Lazily wakup nohz CPU when adding new timer.

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Message-ID: <20151023021951.GP3897@ubuntu>
Date:	Fri, 23 Oct 2015 07:49:51 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Yunhong Jiang <yunhong.jiang@...ux.intel.com>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] timer: Lazily wakup nohz CPU when adding new timer.

On 22-10-15, 14:40, Yunhong Jiang wrote:
> A naive question is, why it's sure a tick will happen when the tickless 
> processor is in idle?

How do you get this impression? I don't think anyone has said that.

We are talking about deferrable timers, which by design are only
required if the target CPU is not-idle. If it is idle, then the timer
isn't required to be serviced until the CPU wakes up. And the CPU can
take whatever time it wants to wake up again.

> Is it because scheduler load balance is sure to send a 
> tick to the processor in future?

No. We aren't expecting the CPU to wake up any time soon. Just ignore
the deferrable timer.

-- 
viresh
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