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From:   David Gow <davidgow@google.com>
Date:   Thu, 19 May 2022 21:15:14 +0800
Message-ID: <CABVgOS=X51T_=hwTumnzL2yECgcshWBp1RT0F3GiT3+Fe_vang@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:     Daniel Latypov <dlatypov@google.com>,
        Brendan Higgins <brendanhiggins@google.com>,
        Shuah Khan <skhan@linuxfoundation.org>,
        Dmitry Vyukov <dvyukov@google.com>,
        KUnit Development <kunit-dev@googlegroups.com>,
        kasan-dev <kasan-dev@googlegroups.com>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Wed, May 18, 2022 at 11:36 PM 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.
>

I tend to agree that having both would be nice: I think there are
enough useful "machine configs" that trying to maintain, e.g, a 1:1
mapping with kernel architectures is going to leave a bunch of things
on the table, particularly as we add more tests for, e.g., drivers and
specific CPU models.

The problem, of course, is that the --kconfig_add flags don't allow us
to override anything explicitly stated in either the kunitconfig or
qemu_config (and I imagine there could be problems with --qemu_config,
too).

> > 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.

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