linux-kernel - Re: vmstat: make vmstat_updater deferrable again and shut down on idle

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Message-ID: <alpine.DEB.2.20.1601210940030.7063@east.gentwo.org>
Date:	Thu, 21 Jan 2016 09:41:28 -0600 (CST)
From:	Christoph Lameter <cl@...ux.com>
To:	Shiraz Hashim <shiraz.linux.kernel@...il.com>
cc:	Michal Hocko <mhocko@...nel.org>, akpm@...ux-foundation.org,
	linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org>,
	hannes@...xchg.org, penguin-kernel@...ove.sakura.ne.jp
Subject: Re: vmstat: make vmstat_updater deferrable again and shut down on
 idle

On Thu, 21 Jan 2016, Shiraz Hashim wrote:

> > On idle we fold counters immediately. So there is no loss of accuracy.
>
> vmstat is scheduled by shepherd or by itself (conditionally). In case shepherd
> is deferred and vmstat doesn't schedule itself, then vmstat needs to wait
> for shepherd to be up and then schedule it. This may end up in delayed status
> update for all live cpus. Isn't it ?

The shepherd runs on a processor with an active tick and thus should do
its duty every 2 seconds as scheduled. Small milisecond range deferrals do
not matter much.