linux-kernel - Re: unwind_init() takes 100 ms

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Message-ID: <20181009061234.GA116930@gmail.com>
Date:   Tue, 9 Oct 2018 08:12:34 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     Paul Menzel <pmenzel@...gen.mpg.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: unwind_init() takes 100 ms

* Josh Poimboeuf <jpoimboe@...hat.com> wrote:

> > 4.  Would a command line parameter be reasonable `disable_unwind`, so people
> > could decrease their boot time with distribution kernels, and easily turn it
> > back on, when they need a stacktrace without having to rebuild the Linux
> > kernel?
> 
> I think a boot cmdline option to disable ORC would be ok.

I don't agree with such a kludge: 100 msecs isn't the end of the world for a
distro kernel bootup which takes a lot longer than that typically, and we'd like to
see the build time sorting implemented as well.

Let's fix this for real intstead of a workaround that is going to decrease
the debuggability of the kernel *significantly*.

> I'm not sure about a runtime toggle though.  It might be racy and I'd
> rather avoid that completely, unless there's a solid justification for
> it.

No, just no ...

Debug facilities need to be robust, dependable and as simple as possible.

Thanks,

	Ingo