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

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Message-ID: <CAPub14_S6swU_SPzZjx_OwyWhPBzXsfaoQ4Xc4qAKTDbtmjPSA@mail.gmail.com>
Date:	Thu, 21 Jan 2016 11:54:49 +0530
From:	Shiraz Hashim <shiraz.linux.kernel@...il.com>
To:	Christoph Lameter <cl@...ux.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 Wed, Jan 20, 2016 at 8:42 PM, Christoph Lameter <cl@...ux.com> wrote:
> On Wed, 20 Jan 2016, Shiraz Hashim wrote:
>
>> The patch makes vmstat_shepherd deferable which if is quiesed
>> would not schedule vmstat update on other cpus. Wouldn't this
>> aggravate the problem of vmstat for rest cpus not gettng updated.
>
> Its only "deferred" in order to make it at the next tick and not cause an
> extra event. This means that vmstat will run periodically from tick
> processing. It merely causes a synching so that we have one interruption
> that does both.
>
> 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 ?

-- 
regards
Shiraz Hashim