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Torvalds Explains Scheduler Decision
Posted by
kdawson
on Sat Jul 28, 2007 02:24 PM
from the it's-the-guy-not-the-code dept.
from the it's-the-guy-not-the-code dept.
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."
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Why Linux Has Failed on the Desktop 995 comments
SlinkySausage writes "Linux is burdened with 'enterprise crap' that makes it run poorly on desktop PCs, says kernel developer Con Kolivas. Kolivas recently walked away from years of work on the kernel in despair. APCmag.com has a lengthy interview with Kolivas, who explains what he sees is wrong with Linux from a performance perspective and how Microsoft has succeeded in crushing innovation in personal computers."
[+]
IT: Torvalds On Pluggable Security Models 216 comments
eldavojohn writes "The KernelTrap highlights an interesting discussion on pluggable security models including some commentary by Linus Torvalds. While Torvalds argued against pluggable schedulers, he's all for pluggable security. Other members were voicing concerns with the pluggable nature of the Linux Security Model, but Torvalds put his foot down and said it stays. When asked why his stance was different between schedulers and security, he replied, 'Schedulers can be objectively tested. There's this thing called 'performance,' that can generally be quantified on a load basis. Yes, you can have crazy ideas in both schedulers and security. Yes, you can simplify both for a particular load. Yes, you can make mistakes in both. But the *discussion* on security seems to never get down to real numbers. So the difference between them is simple: one is hard science. The other one is people wanking around with their opinions.'"
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Torvalds Explains Scheduler Decision
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Linus as the benevolent dictator again (Score:5, Insightful)
Re:Linus as the benevolent dictator again (Score:4, Insightful)
Re:Linus as the benevolent dictator again (Score:4, Informative)
"People who think SD was 'perfect' were simply ignoring reality," Linus Torvalds began in a succinct explanation as to why he chose the CFS scheduler written by Ingo Molnar instead of the SD scheduler written by Con Kolivas. He continued, "sadly, that seemed to include Con too"
Re:Linus as the benevolent dictator again (Score:5, Informative)
lkml full quote of Linus:
> People who think SD was "perfect" were simply ignoring reality. Sadly,
> that seemed to include Con too, which was one of the main reasons that I
> never ended entertaining the notion of merging SD for very long at all:
> Con ended up arguing against people who reported problems, rather than
> trying to work with them.
(from Linus's post to lkml [lkml.org])
The other misrepresentation is in this quote
> As a long-term maintainer, trust me, I know what matters. And a person who
> can actually be bothered to follow up on problem reports is a *hell* of a
> lot more important than one who just argues with reporters.
Because Kolivas was quite good with feedback--arguably better than Ingo or Linus (for example with Linus vs. SCSI-emulation cdrecord)--and recently had the single instance to which Linus refers. Ironically, Kolivas rejected a request to have code renice X processes for the same reason Linus rejected a request to keep SCSI emulation as de-facto: the design and code is cleaner and more correct. In fact, while Con would argue about small design issues and change his views, this renicing instance (some people called out as trolling because of the insistence and seeming insincerity) is the only time I've seen Con (and I have followed his work since he started) flatly and repeatedly reject a request.
There is merit in Linus's argument that a comparison of CFS and SD showed no "significant difference" in performance.
My personal take is that several years of minor spats between Ingo and Con made a better -ck patchset and -mm patchset, but never brought -ck closer to mainline. It came down to the good-old-boy system where Linus knew and trusted Ingo better than Con, and if there was a major disagreement, Ingo's side would be favored. But, honestly, Linus could also be considering that Ingo's resume has always been a programmer's resume (even if Ingo was one of the youngest maintainers at his start) while Con is a self-taught programmer (just to improve kernel responsiveness nonetheless!) with a primary passion as a physician. If Con decides not to continue with the -ck patchset, I am sure he will refocus the extra dedication and time to new patients.
Re:Linus as the benevolent dictator again (Score:5, Interesting)
(http://freegamer.blogspot.com/)
I wrote this comment on kerneltrap [kerneltrap.org].
Christ, that's incredible. Nice one "bconway".
Re:Linus as the benevolent dictator again (Score:4, Interesting)
Re:Linus as the benevolent dictator again (Score:5, Insightful)
(http://www.mrnaz.com/)
If you're so hell bent on bringing MS's flaws into the bright light of community awareness, then stand up, be a fucking man, and apply that same attitude to Linux, or one day you'll wake up and Linux will be just as big a bug ridden piece of shit thanks to you stripping away the very system of honest objective peer review that has kept both the codebase and community bug free.
Re:Linus as the benevolent dictator again (Score:5, Funny)
(http://plaidphantom.livejournal.com/)
Re:Linus as the benevolent dictator again (Score:5, Insightful)
For those of us who are not kernel hackers, (Score:5, Interesting)
Re:For those of us who are not kernel hackers, (Score:5, Informative)
(Last Journal: Friday October 19, @09:21PM)
CFS = completely fair scheduler
SD = staircase deadline.
That probably didn't clarify anything :/
seeming to care is a big deal (Score:5, Insightful)
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.
Re:seeming to care is a big deal (Score:5, Insightful)
It also seems that Linus was tricked into torpedoing Con by people who gave him a very warped account of Con's actions. Either Linus got played and turned into a political tool of some anti-ck people, or he's making it appear that way to seem like an innocent victim. Linus evidently screwed up big-time here... but that should be expected from time to time.
ok, one step further then (Score:5, Informative)
Whether Con was aware of it, when he tried to integrate into mainline Ingo was his main customer. Specifically the person he was trying to deliver work to. And Con committed the cardinal sin of telling a customer that the customer was wrong about what he wanted. Even if Ingo were too coked up to operate a keyboard reliably and had it all wrong, trying that never seems to work.
Did Con gain anything by refusing to re-introduce the hack to get X working the way it had previously under load? Even if he'd just put in a #define that allowed it, and then spent the next year arguing to take it out, there wouldn't have been this breakdown.
Linus, Games are important! (Score:2, Redundant)
The only important points to me are:
1) Games are basic to linux desktops, we need linux games, so if Con scheduler was best on games, please, incorporate those changes.
2) EGO's are a pain in the ass, it seems that Con has been refused by Linus , because he didn't take the whole history into acount, too bad, that kind of things happend in any not trivial project management. Don't let EGO's rule the ball, that's the most basic point a manager (Linus) has to respect to keep people on the project.
Re:Linus, Games are important! (Score:5, Informative)
IIRC that is the reason Con together with another person, whose name I can't
can't be bothered to look up, wanted to merge plugsched to which they got a
reply along the lines of "too much choice will split contributors" [kerneltrap.org] or some such
And then Ingo turns around on himself, and claims something along the lines of
"Oh okay, you should work on plugsched, may be it'll get merged" [kerneltrap.org]
Re:Linus, Games are important! (Score:5, Insightful)
(http://theravensnest.org/ | Last Journal: Sunday October 07, @07:05AM)
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.
Linus wins by default (Score:2, Insightful)
(Last Journal: Sunday October 07, @01:01AM)
Re:Linus wins by default (Score:5, Insightful)
(http://www.sigsegv.cx/)
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.
Re:Linus wins by default (Score:5, Insightful)
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.
Re:Linus wins by default (Score:5, Insightful)
(http://rtfm.insomnia.org/~qg/ | Last Journal: Wednesday November 16 2005, @07:11AM)
Re:Linus wins by default (Score:5, Insightful)
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.
"desktop experience" (Score:3, Interesting)
(http://yro.slashdot.org/~drDugan/)
frankly, really high quality experiences take organizational planning and leveraging the expereince of huge groups in way that the "bazzaar" model of software developemnt in open source does not do well. Would someone please just build a mutual benefit corporation for open source users and maintainers? Let's start paying for project managers and the other experienced professionals required to make a "desktop experience" and you will see Linux take over.
recently released 2.6.23 kernel? (Score:2, Informative)
I find him rather rude (Score:4, Interesting)
Re:I find him rather rude (Score:5, Informative)
Linus is (as I am) a Finn by birth. No matter how long he has been abroad, he still follows Finnish habits and speech patterns at least to a degree. And they differ significantly from the west european tradition. For example, small talk is considered unnecessary or even rude in some situations. Getting to the point is a virtue in any conversation. To someone not familiar with this pattern, it will sound unfriendly! It's a two-way street: to me many english speakers sound terriby smarmy and guarded.
Of course, Linus is apparently also rather clever. The downside of cleverness is for many having little tolerance for fools, real or percieved.
An AFC (Anonymous Finnish Coward)
Re:I find him rather rude (Score:5, Interesting)
(http://alphakilo.com/)
During the same trip I saw the Gulf of Finnland freeze. First salt water body I've seen freeze. And the Finns were thrilled because now the drive to Tallinn was a mere 80 mi round trip, and the booze in Tallinn is tax free.
Ooksie isso olute kiitose...pardon my phonetic spelling
Re:I find him rather rude (Score:4, Informative)
And I don't know if it's only here in Finland, but generally whenever we fall we just try to get up as fast as possible, proceed with whatever we were doing acting like nothing happened, and hope that nobody noticed this embarrassing situation. So somebody helping us up and repeatedly saying how sorry he/she is would just make it worse
-- Another Anonymous Finnish Coward
Re:I find him rather rude (Score:5, Interesting)
(http://simpy.com/user/jkniiv)
Unfortunately the current generation, the kids of these baby boomers (the 20 and 30-somethings of today) don't have the same sense of community that their parents had when they grew up, so they have gone over the top and partially lost their moral compass wrt. what is polite enough to be acceptable. There are signs of a counter-phenomenon emerging as a result of the very good economic growth in Finland's telecommunications sector (read: Nokia) which has increased the number of well-off people considerably and made middle class values somewhat fashionable again. Whether this will make people less rude on icy boardwalks, remains to be seen.
Yksi kuiva siideri, kiitos. Pankille, kiitos.
Re:I find him rather rude (Score:4, Interesting)
This might trample on a few toes but it sure gets the job done.
Re:I find him rather rude (Score:4, Insightful)
Um, no. It's that their definition of polite is not the same as yours.
Re:I find him rather rude (Score:5, Funny)
All these years I thought I was a social misfit, but apparently I'm just Finnish.
Boy will my parents be surprised.
Re:I find him rather rude (Score:4, Funny)
Re:I find him rather rude (Score:5, Funny)
(http://honeypot.net/ | Last Journal: Friday April 07 2006, @09:33AM)
You're going to love this Theo guy, then.
I keed, I keed.
Re:I find him rather rude (Score:5, Insightful)
(http://honeypot.net/ | Last Journal: Friday April 07 2006, @09:33AM)
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".
RTFA and understand (Score:4, Insightful)
(http://datanytt.no/)
Linus admitted to favoritism (Score:5, Insightful)
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.
Re:RTFA and understand (Score:4, Interesting)
The -rt patch will:
- Make latencies deterministic
- Reduce latencies if used correctly
- Add slight over head to overall througput
I think once the -rt patch is merged into the mainline it will work wondersfor games and all sorts of other important things, like industrial automation,
automated stock trading, and other high-speed data acquisition and processing.
So there is a road map to improve scheduling. In fact it's actually a broader and
more appealing plan than just scheduling for the desktop, IMHO. I think this is what
Linus is trying to get at in terms of his why he doesn't want a perfect desktop scheduler.
tfa shows "interesting" view into Linus's outlook (Score:5, Insightful)
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.
"
Re:tfa shows "interesting" view into Linus's outlo (Score:4, Insightful)
(http://jargon-file.org/)
Con Kolivas's reaction to "losing" was not to continue to maintain SD and try to get it in later, or to try to improve CFS, but to quit kernel-hacking entirely. Which means he is not of a temperament that can accept that large projects will have arbitrary decisions that go against him, which means he would be a bad choice for the maintainer of a major kernel system. His actions in retrospect justify Torvalds's judgment that he couldn't trust him as a maintainer. Kolivas proved Torvalds correct on the management question, even if Torvalds is wrong on the technical one.
Re:tfa shows "interesting" view into Linus's outlo (Score:5, Informative)
I fully agree with the first part of your post, but I don't buy this 'Con's reaction justify Linus judgment' argument:
1) It seems clear on the mailing lists that Con was really a good maintainer (only one 'problem' reported).
2) Con's reaction seems quite understandable, after a very long time working on a project you see it not only refused by the maintainers (perfecty ok on that), but suddenly 'copied/inspired/wahtereryouwant' by that very same maintainer (not quite right).
EGO leads to sectarism, that's all. The problem is that it seems that Con's scheduler was very good at gamming, and it's a shame that Linux dimissed a good piece of code on a specially sensible area for personal motives.
Damn right the desktop experience is improved! (Score:3, Interesting)
Why does Linus appear so angry? (Score:2)
After reading over the article, I came away with the impression that Linus appears to be an angry person. I have also noticed this in past topics where emails from Linus have been mentioned. So I am asking the question as to why he appears this way. Is it because I always see such references at particular time like now with hot button issues? Or perhaps because English is not his native tongue? Or is it because he really does have an anger management issue?
Based on his own comments in those emails (and the standards that he seems to hold everyone to) it seems to me that Linus would not work with himself as he himself appears very pig-headed and stubborn.
Anyone care to explain?
Why not both? (Score:5, Interesting)
I know very little about operating systems, schedulers, and maintaining large projects, so please excuse any ignorance in my post
Re:Why not both? (Score:5, Informative)
(http://www.foobarsoft.com/)
Linux doesn't support that, as far as I know. There are variables you can tune though. More on this later.
Something like that is very risky. Where as a filesystem can be used or not, and the code is only hit when accessing it, the scheduler is used constantly. If the scheduler could be switched at runtime, that means that either you have to have some kind of if statement on every scheduler entry point, or hide it all behind a pointer and a structure. Either one isn't as efficient as just having it hard wired in. You also have the complexities of being able to hand stuff off from one scheduler to another. Also, debugging get much harder (you have problem with slowness X, now which of the 3 schedulers are you using? Which version? What are the variables set to?).
As for selectable at