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    SubjectLinux/Pro [was Re: Coding style - a non-issue]
    On Fri, Nov 30, 2001 at 02:17:33PM -0800, Andrew Morton wrote:
    > Larry McVoy wrote:
    > >
    > > Linux isn't there yet
    > > and unless the development model changes somewhat, I'll stand behind my
    > > belief that it is unlikely to ever get there.
    > I am (genuinely) interested in what changes you think are needed.

    Well I have an opinion, not sure if it will be well received or not,
    but here goes.

    There is a choice which needs to be made up front, and that is this:

    do you want to try and turn the Linux kernel hackers into Sun style
    hackers or do you want to try something else?

    This assumes we have agreement that there is a difference between the
    two camps. I'd rather not get into a "this way is better than that way"
    discussion, let's just postulate that the Sun way has some pros/cons
    and so do the Linux way.

    If you want to try and make Linux people work like Sun people, I think
    that's going to be tough. First of all, Sun has a pretty small kernel
    group, they work closely with each other, and they are full time,
    highly paid, professionals working with a culture that is intolerant of
    anything but the best. It's a cool place to be, to learn, but I think
    it is virtually impossible to replicate in a distributed team, with way
    more people, who are not paid the same or working in the same way.

    Again, let's not argue the point, let's postulate for the time being
    that the Linux guys aren't going to work like the Sun guys any time soon.

    So what's the problem? The Sun guys fix more bugs, handle more corner
    cases, and scale up better (Linux is still better on the uniprocessors
    but the gap has narrowed considerably; Sun is getting better faster than
    Linux is getting better, performance wise. That's a bit unfair because
    Linux had, and has, better absolute numbers so there was less room to
    improve, but the point is that Sun is catching up fast.)

    As the source base increases in size, handles more devices, runs on more
    platforms, etc., it gets harder and harder to make the OS be reliable.
    Anyone can make a small amount of code work well, it's exponentially
    more difficult to make a large amount of code work well. There are lots
    of studies which show this to be true, the mythical man month is a good
    starting place.

    OK, so it sounds like I'm saying that the Linux guys are lame, Sun is
    great, and there isn't any chance that Linux is going to be as good
    as Solaris. That's not quite what I'm saying. *If* you want to play
    by the same rules as Sun, i.e., develop and build things the same way,
    then that is what I'm saying. The Linux team will never be as good
    as the Sun team unless the Sun team gets a lot worse. I think that's
    a fact of life, Sun has 100s of millions of dollars a year going into
    software development. ESR can spout off all he likes, but there is no
    way a team of people working for fun is going to compete with that.

    On the other hand, there is perhaps a way Linux could be better. But it
    requires changing the rules quite a bit.

    Instead of trying to make the Linux hackers compete with the Sun hackers,
    what would happen if you architected your way around the problem?
    For example, suppose I said we need to have a smaller, faster, more
    reliable uniprocessor kernel. Suppose I could wave a magic wand and
    make SMP go away (I can't, but bear with me for a second). The problem
    space just got at least an order of magnitude less complex than what Sun
    deals with. I think they are up to 32-64 way SMP and you can imagine,
    I hope, the additional complexity that added. OK, so *if* uniprocessor
    was the only thing we had to worry about, or say 2-4 way SMP with just
    a handful of locks, then can we agree that it is a lot more likely that
    we could produce a kernel which was in every way as good or better than
    Sun's kernel, on the same platform? If the answer is yes, keep reading,
    if the answer is no, then we're done because I don't know what to do if
    we can't get that far.

    For the sake of discussion, let's assume that you buy what I am saying
    so far. And let's say that we agree that if you were to toss the SMP
    stuff then we have a good chance at making a reliable kernel, albeit
    an uninteresting one when compared to big boxes. If you want me to go
    into what I think it would take to do that, I will.

    The problem is that we can't ignore the SMP issues, it drives hardware
    sales, gets press, it's cool, etc. We have to have both but the problem
    is that if we have both we really need Sun's level of professionalism
    to make it work, and it isn't realistic to expect that from a bunch of
    underpaid (or not at all paid) Linux hackers.

    Here's how you get both. Fork the development efforts into the SMP part
    and the uniprocessor part. The uniprocessor focus is on reliability,
    stability, performance. The SMP part is a whole new development effort,
    which is architected in such a way as to avoid the complexity of a
    traditional SMP implementation.

    The uniprocessor team owns the core architecture of the system. The
    abstractions provided, the baseline code, etc., that's all uni. The
    focus there is a small, fast, stable kernel.

    The SMP team doesn't get to touch the core code, or at least there is
    a very strong feedback loop against. In private converstations, we've
    started talking about the "punch in the nose" feedback loop, which means
    while it may be necessary to touch generic code for the benefit of SMP,
    someone has to feel strongly enough about it that they well sacrifice
    their nose.

    It would seem like I haven't solved anything here, just painted a nice
    but impossible picture. Maybe. I've actually thought long and hard
    about the approach needed to scale up without touching all the code
    and it is radically different from the traditional way (i.e., how
    Sun, SGI, Sequent, etc., did it). If you are interested in that, I'll
    talk about it but I'll wait to see if anyone cares.

    The summary over all of this is:

    If you want to solve all the problems that Sun does, run on the same
    range of UP to big SMP, Linux is never going to be as reliable as
    Solaris. My opinion, of course, but one that is starting to gain
    some traction as the OS becomes more complex.

    That leaves you with a choice: either give up on some things,
    magically turn the Linux hackers into Sun hackers, or
    architect your way around the problem.

    My vote is the last one, it fits better with the Linux effort, the answer
    is way more cool than anything Sun or anyone else has done, and it lets
    you have a simple mainline kernel source base.
    Larry McVoy lm at
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