Re: [PATCH] tools: selftests - create a separate hotplug target

[Shuah Khan]

On 06/27/2014 01:45 PM, Andrew Morton wrote:
> On Fri, 27 Jun 2014 11:10:37 -0600 Shuah Khan <shuah.kh@xxxxxxxxxxx> wrote:
>
> > On 06/26/2014 03:51 PM, Andrew Morton wrote:
> > > On Thu, 26 Jun 2014 14:33:56 -0600 Shuah Khan <shuah.kh@xxxxxxxxxxx> 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?
>
> I don't know really.  You know more about this than I - what advantages
> does the separate-make-target approach have over this approach?

Currently these tests run with full range - i.e try to offline
all cpus that are hotpluggable and try to offline all memory
that is hotpluggable. This results in hangs.

Creating a separate target the way I did it in this patch excludes these
tests all together. i.e when somebody runs:

make -C tools/testing/selftests run_tests

hotplug tests don't run.

Instead, with a few changes, tests can be run with a reduced scope so
a % of the memory gets offlined as opposed to all of it and the same
thing with cpus. This way hotplug code gets tested as opposed to
being excluded in a default test run case.

However, if limited scope testing isn't useful, separate target is
better until tests can be made safe to run without hangs.

-- Shuah

--
Shuah Khan
Senior Linux Kernel Developer - Open Source Group
Samsung Research America(Silicon Valley)
shuah.kh@xxxxxxxxxxx | (970) 672-0658
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/