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From:   Marco Elver <elver@google.com>
Date:   Wed, 18 May 2022 17:35:40 +0200
Message-ID: <CANpmjNPSm8eZX7nAJyMts-4XdYB2ChXK17HApUpoHN-SOo7fRA@mail.gmail.com>
Subject: Re: [PATCH 1/2] kunit: tool: Add x86_64-smp architecture for SMP testing
To:     Daniel Latypov <dlatypov@google.com>
Cc:     David Gow <davidgow@google.com>,
        Brendan Higgins <brendanhiggins@google.com>,
        Shuah Khan <skhan@linuxfoundation.org>,
        Dmitry Vyukov <dvyukov@google.com>, kunit-dev@googlegroups.com,
        kasan-dev@googlegroups.com, linux-kselftest@vger.kernel.org,
        linux-kernel@vger.kernel.org
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On Wed, 18 May 2022 at 17:31, Daniel Latypov <dlatypov@google.com> wrote:
>
> On Wed, May 18, 2022 at 12:32 AM 'David Gow' via KUnit Development
> <kunit-dev@googlegroups.com> wrote:
> >
> > Add a new QEMU config for kunit_tool, x86_64-smp, which provides an
> > 8-cpu SMP setup. No other kunit_tool configurations provide an SMP
> > setup, so this is the best bet for testing things like KCSAN, which
> > require a multicore/multi-cpu system.
> >
> > The choice of 8 CPUs is pretty arbitrary: it's enough to get tests like
> > KCSAN to run with a nontrivial number of worker threads, while still
> > working relatively quickly on older machines.
> >
>
> Since it's arbitrary, I somewhat prefer the idea of leaving up
> entirely to the caller
> i.e.
> $ kunit.py run --kconfig_add=CONFIG_SMP=y --qemu_args '-smp 8'
>
> We could add CONFIG_SMP=y to the default qemu_configs/*.py and do
> $ kunit.py run --qemu_args '-smp 8'
> but I'd prefer the first, even if it is more verbose.
>
> Marco, does this seem reasonable from your perspective?

Either way works. But I wouldn't mind a sane default though, where
that default can be overridden with custom number of CPUs.

> I think that a new --qemu_args would be generically useful for adhoc
> use and light enough that people won't need to add qemu_configs much.
> E.g. I can see people wanting multiple NUMA nodes, a specific -cpu, and so on.