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From:   Daniel Latypov <dlatypov@google.com>
Date:   Wed, 18 May 2022 08:39:16 -0700
Message-ID: <CAGS_qxr4vTSEtcGGFyoZibga2Q_Avp9pFD78GOA3W9o6F9RVRQ@mail.gmail.com>
Subject: Re: [PATCH 1/2] kunit: tool: Add x86_64-smp architecture for SMP testing
To:     Marco Elver <elver@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, May 18, 2022 at 8:36 AM Marco Elver <elver@google.com> wrote:
>
> 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.
>

Ack.
Let me clean up what I have for --qemu_args and send it out for discussion.

One downside I see to adding more qemu_configs is that --arch now
becomes more kunit-specific.
Before, a user could assume "oh, it's just what I pass in to make ARCH=...".
This new "--arch=x86_64-smp" violates that. I don't personally see it
being that confusing, but I still worry.