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

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Message-ID: <87ehf7b6o7.fsf@linaro.org>
Date:	Fri, 22 Mar 2013 12:01:12 -0700
From:	Kevin Hilman <khilman@...aro.org>
To:	paulmck@...ux.vnet.ibm.com
Cc:	Christoph Lameter <cl@...ux.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Rob Landley <rob@...dley.net>, linux-kernel@...r.kernel.org,
	josh@...htriplett.org, zhong@...ux.vnet.ibm.com,
	geoff@...radead.org, tglx@...utronix.de
Subject: Re: [PATCH] nohz1: Documentation

[...]

>> >
>> > In the meantime, one approach is to bind all these SCHED_OTHER tasks
>> > to designated housekeeping CPU(s) that don't run your main workload.
>> 
>> One cannot bind kevent threads and other per cpu threads to another
>> processor. So right now there is no way to avoid this issue.
>
> Yep, my approach works only for those threads that are free to migrate.
> Of course, in some cases, you can avoid per-CPU threads running by pinning
> interrupts, avoiding certain operations in your workload, and so on.

Speaking of threads that are not free to migrate, you might add a bit to
the doc explaining that these various kernel threads that cannot migrate
are also potential sources of jitter and also reasons why a CPU may exit
(or not enter) full nohz mode.

And thanks a ton for writing up this detailed doc.  Speaking as someone
trying to get full nohz working on a new arch (ARM), getting my head
around all of this has been challenging, and your doc is a great help.

Kevin
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