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From:   Daniel Latypov <dlatypov@google.com>
Date:   Wed, 18 May 2022 08:31:27 -0700
Message-ID: <CAGS_qxrOUYC5iycS436Rb-gEoEnYDa2OJLkQhEVXcDN0BEJ4YA@mail.gmail.com>
Subject: Re: [PATCH 1/2] kunit: tool: Add x86_64-smp architecture for SMP testing
To:     David Gow <davidgow@google.com>
Cc:     Brendan Higgins <brendanhiggins@google.com>,
        Marco Elver <elver@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, 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?

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.