linux-kernel - Re: [PATCH] nohz1: Documentation

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Message-ID: <CAFTL4hyfQ_R=FA92aFWBmKA_4yp6CtStgz1fR71mJOKCbiCQAQ@mail.gmail.com>
Date:	Mon, 25 Mar 2013 16:20:50 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Christoph Lameter <cl@...ux.com>
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Rob Landley <rob@...dley.net>, linux-kernel@...r.kernel.org,
	josh@...htriplett.org, zhong@...ux.vnet.ibm.com,
	khilman@...aro.org, geoff@...radead.org, tglx@...utronix.de
Subject: Re: [PATCH] nohz1: Documentation

2013/3/25 Christoph Lameter <cl@...ux.com>:
> On Mon, 25 Mar 2013, Frederic Weisbecker wrote:
>
>> > The vm kernel threads do no useful work if no system calls are being done.
>> > If there is no kernel action then they can be deferred indefinitely.
>> >
>>
>> We can certainly add some user deferrable timer_list. But that's going
>> to be for extreme usecases (those who require pure isolation) because
>> we'll need to settle that with a timer reprogramming into user/kernel
>> boundaries. That won't be free.
>
> These timers are already marked deferrable and are deferred for the idle
> dynticks case. Could we reuse the same logic? See timer.h around the
> define of TIMER_DEFERRABLE. I just assumed so far that the dyntick idle
> logic would have been used for this case.

We need to audit all deferreable timers to check if their
deferrability in idle also applies for userspace. If so may be we can
consider that.
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