linux-kernel - Re: [PATCH] nohz: make the idle_entrytime/idle

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Message-ID: <20150918184213.GA31162@jnakajim-build>
Date:	Fri, 18 Sep 2015 11:42:13 -0700
From:	Yunhong Jiang <yunhong.jiang@...ux.intel.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] nohz: make the idle_entrytime/idle_exittime correct

On Thu, Sep 17, 2015 at 11:45:37PM +0200, Thomas Gleixner wrote:
> On Wed, 16 Sep 2015, Yunhong Jiang wrote:
> 
> > Currently the idle_entrytime is updated on idle_entry, idle_exit and
> > get_cpu_idle/iowait_time_us() with non-NULL parameter. This makes the
> > idle_entrytime not the real entrytime anymore. The idle_exittiime is
> > updated when exit tickless state, which can be idle tickless or full
> > tickless.
> 
> If something calls one of the functions then the cpu is not idle. It's
> running code.

I think the get_cpu_idle/iowait_time_us() can be called from other CPUs.

Hmm, I should state this patch as "no idle_entrytime update on
get_cpu_idle/iowait_time_us()". If you think this statement is correct,
I will re-submit a patch for it.

>  
> > Change the idle_entrytime to be updated only when enter idle, the
> > idle_exittime to be updated only when exit idle. Update
> > the get_cpu_idle_iowait_time_us() accordingly.
> 
> And the rationale for this change is?

I tried to check /proc/timer_list for idle_entrytime/idle_exittime, and
noticed this when reading the corresponding code. So no special reason for
this change, just correctness.

Thanks
--jyh

> 
> Thanks,
> 
> 	tglx
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