On Wed, 2019-10-16 at 13:08 +0000, Luis Chamberlain wrote:
On Wed, Oct 16, 2019 at 12:52:12PM +0200, Knut Omang wrote:
On Mon, 2019-10-14 at 13:01 -0600, shuah wrote:
On 10/14/19 12:38 PM, Knut Omang wrote:
On Mon, 2019-10-14 at 10:42 +0000, Luis Chamberlain wrote:
On Fri, Sep 13, 2019 at 02:02:47PM -0700, Brendan Higgins wrote:
Hey Knut and Shuah,
Following up on our offline discussion on Wednesday night:
We decided that it would make sense for Knut to try to implement Hybrid
Testing (testing that crosses the kernel userspace boundary) that he
introduced here[1] on top of the existing KUnit infrastructure.
We discussed several possible things in the kernel that Knut could test
with the new Hybrid Testing feature as an initial example. Those were
(in reverse order of expected difficulty):
1. RDS (Reliable Datagram Sockets) - We decided that, although this was
one of the more complicated subsystems to work with, it was probably
the best candidate for Knut to start with because it was in desperate
need of better testing, much of the testing would require crossing
the kernel userspace boundary to be effective, and Knut has access to
RDS (since he works at Oracle).
Any update on if you are able to explore this work.
I am working on this, but it's going to take some time, as this ties in
with internal projects at Oracle. Basing work on RDS or RDS related tests
(such as generic socket etc) is the best option for us, since that allows
progress on our internal deliverables as well ;-)
2. KMOD - Probably much simpler than RDS, and the maintainer, Luis
Chamberlain (CC'ed) would like to see better testing here, but
probably still not as good as RDS because it is in less dire need of
testing, collaboration on this would be more difficult, and Luis is
currently on an extended vacation. Luis and I had already been
discussing testing KMOD here[2].
I'm back!
I'm also happy and thrilled to help review the infrastructure in great
detail given I have lofty future objectives with testing in the kernel.
Also, kmod is a bit more complex to test, if Knut wants a simpler *easy*
target I think test_sysctl.c would be a good target. I think the goal
there would be to add probes for a few of the sysctl callers, and then
test them through userspace somehow, for instance?
That sounds like a good case for the hybrid tests.
The challenge in a kunit setting would be that it relies on a significant
part of KTF to work as we have used it so far:
- module support - Alan has been working on this
I see the patches. Thanks for working on this.
- netlink approach from KTF (to allow user space execution of kernel
part of test, and gathering reporting in one place)
- probe infrastructure
The complexities with testing kmod is the threading aspect. So that is
more of a challenge for a test infrastructure as a whole. However kmod
also already has a pretty sound kthread solution which could be used
as basis for any sound kernel multithread test solution.
Curious, what was decided with the regards to the generic netlink approach?
Can this work be be done without netlink approach? At least some of it.
I would like to see some patches and would like to get a better feel
for the dependency on generic netlink.
A flexible out-of-band communication channel is needed for several of the
features, and definitely for hybrid tests. It does not need to be netlink
in principle, but that has served the purpose well so far in KTF, and
reimplementing something will be at the cost of the core task of getting more
and better tests, which after all is the goal of this effort.
I don't think you did justice to *why* netlink would be good, but in
principle I suspect its the right thing long term if we want a nice
interface to decide what to test and how.
I tried to do that in my response here to Brendan:
https://lore.kernel.org/linux-kselftest/644ff48481f3dd7295798dcef88b4abcc8695260.camel@xxxxxxxxxx/
So kselftest today implicates you know what you want to test. Or rather
this is defined through what you enable and then you run *all* enabled
kselftests.
Similar logic follwos for kunit.
The same applies to KTF.
The trivial default user application for KTF
(see https://lkml.org/lkml/2019/8/13/101,
file tools/testing/selftests/ktf/user/ktfrun.cc)
would run all the kernel tests that has been enabled
(depending what test modules that have been inserted).
But if I just want to run a single test, or I want to randomize
the order the tests are run (to avoid unintended interdependencies),
or whatever other ideas people might have
outside the default setup, KTF offers that flexibility via netlink,
and allows use of a mature user land unit test suite to facilitate
those features, instead of having to reinvent the wheel in kernel code.
Yes, you can have scripts and your own tests infrastructure that knows
what to test or avoid, but this is not nice for autonegotiation.
We haven't really been setting out to do anything ambitions it this area
with KTF, except that we have been using simple naming of tests into
classes and used wilcards etc to run a subset of tests.
Consider also the complexity of dealing with testing new tests on older
kenrels. Today we address this on kselftests by striving to make sure
the old scripts / tests work or yield for old kernel who don't have
a feature. What if we want to really figure out what is there or not
concretely?
A generic netlink interface could easily allow for these
sorts of things to grow and be auto negotiated.
In general I agree that such types of negotiation is something that
can be explored. You can view the KTF code to set up network contexts as
something of a start in that sense. We have code in place that uses
such network context configuration to allow a unit test suite
to exchange address information as part of a single program multiple
data (SPMD) program, using MPI, to allow unit tests that requires
more than a single node to run.
Then, collection of results: we have each kselftest desiging its own
scatter/gather set of way to go and do what it can to test what it can
and expose what should be tested, or in what order, or to allow knobs.
A generic netlink interface allows a standard interface to be sketched
up.
I think we solve this by exposing flexibility to user space.
Why you would want to have the kernel involved in that instead of
just giving user mode enough info?
I don't think the generic netlink interface implemented in the KTF
patches accomplished any of this, but it at least moved the needle
forward IMHO in terms of what we should consider long term.
It would be really good if more people had a closer look at the KTF patch
set before we embark on significant work of porting it to Kunit.
For reference, the netlink code in KTF:
https://lkml.org/lkml/2019/8/13/92
I read it, and it seems like a lot of stuff implemented but without
a lot of proper justification and also without a lot of community
feedback. Kind of like: too much done in house without proper feedback.
Then it became bloated and once kunit was almost about to be merged
you guys knee-jerk reacted and wanted to merge your stuff too...
Again, just for the record, the fact is that we presented KTF
at LPC in 2017 (see https://lwn.net/Articles/735034/) and pushed
it to github for review and comments at the same time
(https://github.com/oracle/ktf).
Looking in the git repo, this was just a few weeks after the initial
refactoring from a project specific predecessor was complete.
I discussed collaboration with Brendan, who had a very early draft
of what later became Kunit with him, and expected from our conversation
that we would work together on a common proposal that covered both main
use cases.
As to the features we added to KTF, they were in response to real test needs
(multithreaded test execution, override of return values to verify
error codepaths, the need for environment/node specific configuration like
different device presence/capabilities, different network configurations
of the test nodes, and so on..
And the quality of code. Gosh, much to be said about that...
We're of course happy to take constructive critics - do you have
any specifics in mind?
So I think that asking to consolidate with kunit is the right thing
at this point. Because we need to grow it in *community*. kunit itself
has been heavily modifed to adjust to early feedback, for example, so
its an example of evolution needed.
Note that unlike kunit, in KTF no tests are executed by default,
instead KTF provides an API to query about, set up and trigger execution of
tests and test parts in the kernel, and leave the actual initiation
to user space tools.
This is all excellent. However baby steps. Let's demo it with a few
simple tests, rather than trying to ensure it works with *all* the
stuff you guys probably already have in house. That will probably have
to be phased out in the future with whatever we grow *together*.
Which brings me back to my original request for (constructive) feedback
on what we already have created.
