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Torvalds Explains Scheduler Decision
Firedog writes "There's been a lot of recent debate over why Linus Torvalds chose the new CFS process scheduler written by Ingo Molnar over the SD process scheduler written by Con Kolivas, ranging from discussing the quality of the code to favoritism and outright conspiracy theories. KernelTrap is now reporting Linus Torvalds' official stance as to why he chose the code that he did. 'People who think SD was "perfect" were simply ignoring reality,' Linus is quoted as saying. He goes on to explain that he selected the Completely Fair Scheduler because it had a maintainer who has proven himself willing and able to address problems as they are discovered. In the end, the relevance to normal Linux users is twofold: one is the question as to whether or not the Linux development model is working, and the other is the question as to whether the recently released 2.6.23 kernel will deliver an improved desktop experience."
As it seems many others don't agree to his opinions of Con, http://lkml.org/lkml/2007/7/27/426
Having had my fair share disagreements with customers over technical issues, it just isn't worth trying to "win." The damage to your working relationships is still there even if you are shown to be 100% right. Try and help them address their problems as much as you possibly can, while trying to compromise as little as possible of the design. It's called diplomacy, and it's the difference between being given huge amounts of responsibility, and wanting to quit. You don't even have to agree with them, you just have to make them think you care.
Finally, it is common for programmers to try to avoid a subset of the problems in an area because it gives them the ability to write something "correct." Certainly a very satisfying experience for a programmer. However, that is exactly why it can be a bad idea to let a programmer rewrite a messy module. Very soon you can find the users of that module asking why a laundry list of things don't work anymore and an idealist developer trying to argue that they shouldn't... And it is exactly those idealists that like to rewrite working code. Not that major rewrites are bad, just that they have to be approached by someone mature enough to both expect a list of things they overlooked, and be willing to work with customers to resolve them.
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I find Linus' comments very interesting, and very honest. He has good arguments, and to me it seems like he did the right thing. He is even open to change scheduler if someone can prove that SD does a better job than CFS, and get someone reliable to maintain it.
It's an interesting set of emails. In addition to admitting that he actually didn't have any problem with the SD code, Linus points out that he made a gut call that Con is difficult to deal with without even looking into it because, apparently on near religious grounds, he doesn't believe in reading "specialized" mailing lists. What i find of concern is that he'd express such strong opinions about people basically without having even spent an hour or two browsing some list archives. Further, he seems perfectly aware that he may have heard just one side of the story, and yet he STILL doesn't feel he needs to look into it further or to soften his view? WTF ?
... arbitrary ?
Has Linux kernel development always been this
From TFA (actually form the quoted emails) after several mails where Linus has been bashing this Con Kolivas guy for not taking feedback and being argumentative, and then offers some statements about the virtues of a good maintainer some guy "Kasper Sandberg" asks him:
"Okay, i wasn't going to ask, but i'll do it anyway, did you even read the
threads about SD?"
to which Linus responds:
"I don't _ever_ go on specialty mailing lists. I don't read -mm, and I
don't read the -fs mailing lists. I don't think they are interesting.
And I tried to explain why: people who concentrate on one thing tend to
become this self-selecting group that never looks at anything else, and
then rejects outside input from people who hadn't become part of the 'mind
meld'.
That's what I think I saw - I saw the reactions from where external people
were talking and cc'ing me.
And yes, it's quite possible that I also got a very one-sided picture of
it. I'm not disputing that.
"
That's not really fair. Slashdot pretty much covers all things science, be it computer science, or quantum physics. There are frequently articles posted which I, being in the field of computer science, do not necessarily understand or comprehend. I'm not going to tell all of the quantum physicists out there that "slashdot is not the place for them" because Slashdot IS for them. While it might have a technical slant to it, I think it's a place for anyone more interested in hearing news of advancements in various scientific fields, rather than what prison Paris Hilton is going to next.
For that matter, even when I don't understand what an article is talking about, I am still usually more than interested to read about it.
Whatever way you want to paint it, that's exactly what he did.
He believes that Ingo is a more reliable maintainer, so he chose Ingo's few-day old hack instead of Con's very mature and well tested scheduler.
Personally, I think that the person who is at fault here is Ingo, because he has a "Not Invented Here / By Me" mentality, and instead of developing Con's scheduler further, he totally objected to Con's work for ages (which prevented it from getting into mainline), and then suddenly saw the light and wrote his own quick hack based on the same design.
Ingo may be a good developer and maintainer, but he sure as hell isn't a friendly co-developer.
Well...
If we look at the core linux developers every single one of them has been flamed into a crisp by Linus on the average every few years (and some of them flamed back in turn). Every single one of them has had something turned down in flames and an alternative merged as well (in some cases Linus admitting that he made the wrong choice later). And I cannot recall anyone of them behaving like such a hissy primadonna.
Similarly, I have flamed people in a crips at work, I have been flamed back and I still work with this people 8+ years later. In some cases we have even come again to the same company and the same team to work together. It is just software, it is just a job and any code you have ever written can and would be ripped out by the project leader one day to be replaced by something else. Accepting this as a given is a sign of maturity. If you cannot do that, you are not mature enough to maintain a critical part of a software project. You should go away and play with toys in the sandpit for a while until you grow up.
Sorry, the guy does not get a bit of my sympathy.
Baker's Law: Misery no longer loves company. Nowadays it insists on it
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The situation for Linux is even simpler, since hardly anyone actually uses the stock kernel. Most Linux users use a kernel supplied by a distribution, which is compiled with a specific set of options and typically a few hundred patches. If one scheduler is good for desktops, and one good for servers, then merge them both and let desktop-focussed distros pick one and server-focussed ones pick the other.
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This is a nonsense idea of a way of life. Life's too short to carry on with a task that is thankless, has lost its enjoyment, and has taken a toll on your health and relationships. Have you even read Con's side?
There is no taking of balls home, just a clash with the monster egos of the Linux kernel. Don't question Con's maturity because he's made a decision to change his life. This in itself makes you sound seventeen and with no experience of life. There may be two sides to this story, so I won't make a judgement yet, but Linus has hardly shown himself to be broad and balanced in the past, has he?
The uncontrollable ego and senseless flaming that is associated with programming is nothing to be proud of and a block to new blood and new personality types (like Con's) getting involved, leaving us with this self-perpetuating industry of arrogant computer scientists attracting nothing but other arrogant computer scientists who are unmoved in by, and ignorant of, what their users want. Fine if you live in a bubble, but doomed by natural selection.
Furtunately, you're offering just an uninformed (and trivial at that) opinion. Unfortunately, you opinion seems to resonate with a large segment of similarly narrow-minded slashdot users. It is particularly tragic when folks here gravitate toward one steep world view without any desire to explore anything else outside of their comfort zone. It is a good thing that vocal narrow-minded elitist views (irritating as they are) are easy to ignore. The fact that diverse stories make it onto slashdot for all to discuss speaks volumes about that kind of site Slashdot actually is. We choose which stories we wish to participate in. The reality is that no one person (or even groups of persons) gets to define what slashdot is or isn't. Instead of helping to insulting others for not knowing much about the inner workings of the kernel, wouldn't it be more instructive to educate them on a subject which you (presumably) are more knowledgeble of? Instead of pushing your own agenda on a public community, why not take the time to look around and listen to what others may have to offer and then make the effort to make *your* contribution to other who need it? Please understand, I am not trying to attack you personally. I'm sure you're a decent upstanding guy. But the perspective of the opinion you've just expressed comes from a direction that hails from the most unsavory part of this great community, one that insults inteligent people and gives us all a bad name.
Stay sentient. Don't drink bad milk.
A few months before Ingo wrote the O(1) scheduler, he flamed anyone who dared to suggest that an O(n) scheduler is a bad idea. He was *very* aggressive about it, going on and on about why O(n) is best and how O(1) would be worthless. Using Linus's words (about Con), Ingo "ended up arguing against people who reported problems [scheduler linearity], rather than trying to work with them". It therefore seems a bit strange that Linus uses this statement to describe Con, arguing this is why he favors Ingo...
Importantly, Ingo was dead wrong back then (indeed, this is why months after, Ingo came up with the O(1), announcing it as if it was his idea and as if nothing ever happened, not *ever* saying something like "I was wrong, sorry for the flames").
In contrast, Con was right in refusing to pollute the design of SD with Ingo's unfairness discipline. (This is what Linus referred to when he made the "arguing against" statement.) And what do you know? A few years after, Ingo comes up with a "Completely Fair Scheduler"...
I'm in scheduling research for many years. I followed the long Linux scheduling saga, which actually started way before Con was in business. Please believe when I tell you: Linus comments about Con are ludicrous, and petty. This is not Linus's finest hour.
Note however that this does not mean that Linus made the wrong decision: Even though SD is somewhat better than CFS, Ingo is orders of magnitude a better programmer than Con, orders of magnitude more knowledgeable, he gets paid to do the work, has gotten along with Linus for years, and will eventually make CFS as good as SD and even better. This is the real reason for Linus's decision. (Or at least, it should be.)
But the stuff Linus said about Con... well, that's just Linus being small.
Don't worry, there are enough non-knowledgeable people here to mod you down. I must admit that this debate really boils down to Linus and Ingo taking a long time to reach Con's conclusions, and then not being as gracious about it as they could be. Con, of course, was insulted by this (who wouldn't be?) and all the while we had two major camps of Linux users: the pro-CK one (holy crap! My system works with this patchset!) and the anti-CK one (damn! My server doesn't need this, wtf?).
In the end this just demonstrates that having egotistical bastards running the show isn't always going to yield the best results. Linus and Ingo do fantastic work, and they do sub-par work. But when someone points the sub-par stuff out, head for the hills! They will always have a legion of fans defending them, more than willing to dumb-down the real issue in favor of pretending their infallible leaders are never wrong.
It's not that they are rude, its just that they don't care so much about being polite.
Um, no. It's that their definition of polite is not the same as yours.
This whole situation reminds me a lot of devfs. The developer of devfs (Richard Gooch) was maybe a bit of an outsider with good ideas and strong opinions that sometimes clashed with those of kernel developers that were more insiders or closer to Linus. The story is a little different in that devfs had actually made it into the mainline kernel, but then later was replaced by udev (the first draft of which was by Greg KH in a day or so... again very much like Ingo's whipping up the first draft of CFS).
/lot/ of energy into their work. But that energy was not lost to the rest of us, as without the experience of their groundbreaking we would not have gotten the solutions we eventually did. Even if Greg KH's udev and Ingo's CFS share no appreciable amount of code or algorithms with devfs and SD, if they are honorable, I'm sure they would admit that they could not have so quickly whipped up their solutions without the example and inspiration of RG and CK's work.
/Maybe/ instead of losing them in the long run we could have gotten some more innovation from talented developers like RG and CK. The problem, I think, wasn't the decision adopt CFS instead of SD. Rather, regardless of whether or not is true, the problem is Linus's public judgement that CK is not a "responsive maintainer". I didn't follow the CK or the lkml lists in that time frame enough to know if he is right... but a really good leader would not have made such a judgement public even if hed believed it, and instead would have worked to find a way to keep such talented persons contributing.
Then as now with CK, eventually Richard stopped doing linux kernel work altogether. I thought it was a sad loss of a talented kernel hacker, and I had been a devfs user, but I must say that in retrospect I do think udev is a better solution. It is simpler, has less impact on the rest of the kernel, but has proven itself to solve all the problems devfs tried to solve that actually mattered.
What's the moral of the story? That both sides are right... on the one hand, there's something sad here, because at least several times in linux history an outsider had to fight for innovation and in the end was pushed away even as his innovation was grudgingly adopted by reinventing it. On the other hand the actual results do seem to indicate that linux is NOT resistant to change, and maybe that the better, more maintainable solution tends to win out.
There's also another thing to keep in mind... it is a pattern in this history of technology that the first attempt to solve a problem is rarely the one that becomes dominant. Both Con Kolivas and Richard Gooch should be recognized for the innovators that they are... and if they were wise they should also not begrudge the fact that it wasn't their exact solution which eventually got adopted by the mainstream. I know this is difficult... they both put a
Finally, I would like to add that although the way I see all this, it has little if anything to do with Linus's personality, nevertheless I think Linus could have handled these cases better.
How we know is more important than what we know.
I love it when web denizens who know only how to code 'html' love to bring in their views of someones motives.
Con didnt take his ball and go home, he finished what he started, did a damn fine job and is now moving to something else in his life which is going to be hard for computer geeks to understand.
The man does not live and breath technology, its just a hobby. By profession he is a doctor; a specialist in anaesthesia.
I got to know him when he was working on a benchmarking tool called Contest and truly is a renaissance man. I appreciate Stallman's knowledge of french, spanish, and of literature but he is a computer geek first and foremost.
Con will probably take up some other intellectual challenge like he did coding and be good at it too. He doesnt NEED to do just this and many cannnot grasp that.
Life is really too short to deal with egos when you are talented and have full of interests.
Doctor Colivas will do just fine.
I think you mistake politeness for submissiveness. For example:
You can be polite and respectful without being a pushover. This is also commonly referred to as "tact".
Dewey, what part of this looks like authorities should be involved?