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Date:	Fri, 27 Jun 2014 11:10:37 -0600
From:	Shuah Khan <>
To:	Andrew Morton <>
	Shuah Khan <>
Subject: Re: [PATCH] tools: selftests - create a separate hotplug target

On 06/26/2014 03:51 PM, Andrew Morton wrote:
> On Thu, 26 Jun 2014 14:33:56 -0600 Shuah Khan <> wrote:
>> On some systems, hotplug tests could hang forever waiting for cpu and
>> memory to be ready to be offlined. A special hotplug target is created,
>> which will help run non-hotplug tests and run hotplug tests as a special
>> case. Individual hotplug tests can still be run as a special target
>> targeted for a single subsystem.
> This is a bit sad.  The general philosophy with selftests is that they
> should run to completion even if the kernel/hardware which they are
> testing isn't available - they should work it out for themselves.
> But that's obviously a problem with hotplug.  And with networking or
> anything else which needs external action.
> On the other hand, networking has loopback and the kernel supports cpu
> hotplug simulation via procfs.  So perhaps the cpu and memory hotplug
> tests should be redone so they do the plug/unplug injection themselves,
> so they can run without external intervention?

Changing/running the tests in a safe mode (least possibility of hang)
mode is another option. This way the tests are run in normal mode with
reduced scope. Memory hotplug test has the ratio option and when I
specified low ratio 1-5%, it completed in a few seconds.

cpu-hotplug test will require changes. I am working on a change to
offline a user specified # of cpus instead offlining all hotpluggable
cpus and then onlining them again at the end of the test.

When all selftests are run, safe mode hotplug tests will be run.

Does this approach sound reasonable?

-- Shuah

Shuah Khan
Senior Linux Kernel Developer - Open Source Group
Samsung Research America(Silicon Valley) | (970) 672-0658
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