New Scheduler Available for FreeBSD

flynn_nrg writes "Luigi Rizzo, one of the FreeBSD developers, has just finished the code for a new scheduler. From the announcement: '...as promised, a first version of the Proportional Share scheduler that we developed is available here. These are for a recent -STABLE (i think any version from 4.4 should work; the only 3 files modified are kern_synch.c, kern_switch.c and proc.h, plus a one-line change to kern_exit.c). I have tested it a little bit on a diskless system, and it seems to survive running a full X session with the usual set of xterm, netscape etc. while i do a "renice" of the processes and even switch back and forth between schedulers. But do not trust this yet for a production system!' Read the full post here."

Comments

No clue what Proportional Share Scheduling is?

[arnoroefs2000]

There's more info here.

Excerpt:

"There are compelling reasons to use proportional share scheduling techniques to support multimedia and other soft real-time applications on general-purpose operating systems. First, proportional share (PS) schedulers are a good match for existing infrastructure such as a periodic timer interrupt and mechanisms for assigning priorities to applications -- priorities can be mapped to shares in a proportional-share environment. Second, PS schedulers provide stronger guarantees to applications than do traditional time-sharing schedulers: they allocate a specific fraction of the CPU to each thread, and some schedulers provide error bounds on the allocation rate. Third, PS schedulers have clear semantics during underload: excess CPU time is allocated fairly, in contrast with some reservation-based schedulers that must idle or back off to a secondary scheduling policy once all application budgets are exhausted."

Re:Why?

[Anonymous Coward]

"There are compelling reasons to use proportional share scheduling techniques to support multimedia and other soft real-time applications on general-purpose operating systems. First, proportional share (PS) schedulers are a good match for existing infrastructure such as a periodic timer interrupt and mechanisms for assigning priorities to applications -- priorities can be mapped to shares in a proportional-share environment. Second, PS schedulers provide stronger guarantees to applications than do traditional time-sharing schedulers: they allocate a specific fraction of the CPU to each thread, and some schedulers provide error bounds on the allocation rate. Third, PS schedulers have clear semantics during underload: excess CPU time is allocated fairly, in contrast with some reservation-based schedulers that must idle or back off to a secondary scheduling policy once all application budgets are exhausted."

Re:Low Latency, Pre-Emptive multitasking?

[Subcarrier]

Don't forget Linux will soon have a new scheduler, too. The O(1) scheduler by Ingo Molnar kicks some serious ass, especially with SMP.

0(1) scheduler

[Sivar]

Is FreeBSD's new one a 0(1) scheduler?
0(1) is a "term" from computer science. When applied to schedulers, it basically means that no matter how many processes there are to schedule, a 0(1) scheduler's overhead will not significantly increase.
Of course, with a small number of threads/processes to schedule, the Linux 0(1) scheduler will have greater initial overhead. It isn't until there are quite a few processes that it starts to show its power, and the more processes there are, the more useful it is.
On a busy server with 4+ processors and thousands of processes, a standard scheduler's overhead is so great that it often exceeds the overhead of most of the individual server processes.

Re:0(1) scheduler

[Osty]

Is FreeBSD's new one a 0(1) scheduler?

Just a nitpick. The term is "O(1)", not "0(1)", as in "Big Oh of 1" and not "Zero of 1".

Re:0(1) scheduler

[dimator]

I prefer ")1(O" just to throw people off.

Darwin?

[BlackGriffen]

Anybody have any idea when/if Apple will integrate improvements from this scheduler in to Darwin/OSX?

Re:Darwin?

[Sivar]

The scheduler is closely tied with the kernel, and MacOSX does not use the FreeBSD kernel at all. It uses the Mach kernel, which is not only a different kernel entirely but a different core kernel philosophy. Mach is a microkernel whereas FreeBSD's is a monolithic kernel. Both types have their advantages and disadvantages, but microkernels are vastly superior for a commercial OS and for driver installations. Monolithic kernels are theoretically faster and easier to implement.

MacOSX gets its BSD label by using the BSD userland utilities. It is great that Mac's OS is no longer junk. In three months I went from "Macs are toy computers for kiddies and Photoshop pros" to "Wow--I can replace every PC and OS in my house with a single Mac! Great desktop, good server, and all the power of Unix."
I have never been happier with the state of Apple Inc.

Re:Darwin?

[Drishmung]

Not quite. This link gives quite bit more background about Darwin. In particular:

Part of the history of Mac OS X goes back to Berkeley Software Distributions (BSD) UNIX of the early seventies. Specifically, it is based in part on BSD 4.4 Lite. On a system level, many of the design decisions are made to align with BSD-style UNIX systems. Many of the libraries are derived from NetBSD (http://www.netbsd.org/), while many of the utilities are from FreeBSD (http://www.freebsd.org/). For future development, Mac OS X has adopted FreeBSD as a reference code base for BSD technology. Work is ongoing to more closely synchronize all BSD tools and libraries with the FreeBSD-stable branch.

Although Mac OS X must credit BSD for most of the underlying levels of the operating system, Mac OS X also owes a major debt to Mach. The kernel is heavily influenced in its design philosophy by Carnegie Mellon's Mach project. The kernel is not a pure microkernel implementation though since the address space is shared with BSD processes.

The Mac OS X kernel (also known as XNU) is a monolithic kernel (unlike Mach, but like Linux and xBSD) with Mach and BSD sitting side-by-side.

Some earlier Apple Unix efforts were true micro kernel implementations. This was also driven by the attraction of a pure hardware abstraction layer. With Darwin this seems to have moved to a more pragmatic recognition that performance matters.

In Darwin, the Mach bits handle memory management, IPC and device drivers. BSD handles users and permissions, the network stack, the virtual file system and POSIX.

So, this won't directly benefit Darwin, though if it is generally useful then someone/anyone can try and put it into Darwin---long live open source! I confess I don't know how the Mach part of Darwin handles scheduling, though I had heard that the Mach VM and scheduling was pretty good.

Re:FreeBSD = Security

[quantum bit]

None of the FreeBSD releases, or the -STABLE branch were vulnerable to the openssh bug.

ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/advisories/ FreeBSD-SA-02:31.openssh.asc

Note the absence of any released version of FreeBSD.

FreeBSD ~= Security

[Sivar]

I am not going to claim that FreeBSD is perfect, but FreeBSD is more secure than the vast majority of Linux-based OSes. It has supported features like the new "GR Security" patch for years, and because it shares a great deal of code with OpenBSD which is audited frequently, it benefits from their work as well.
Of note is that FreeBSD's libc is just over half the size of Linux's Glibc (not that has a thing to do with security)

With FreeBSD, for years, admins have been able to set certain files as "append only" (so even root can only add to, not remove from, log files) and "immutable" (so even root cannot modify or delete the file) and has been able to set firewall rules to the same (immutable) so that creative crackers can't add their personal favorites if they root the system.
This can of course be bypassed by restarting the machine in single-user mode and redusing the kernel security level, but that isn't going to be very easy for your average remote hacker. :)

Furthermore, since 4.0 you can multiple run complete but separate entire copies of FreeBSD on the same system, each with their own FreeBSD system files and such. You can have a single server run an instance of FreeBSD for Apache, one for Postfix, one for BIND, etc. and if any one of them does get compromised (say, BIND since that happens entirely too often) the cracker can not only not effect any of the other instances--he/she cannot even see that they exist! Very interesting stuff.
Of course, IMHO Linux is worlds ahead of FreeBSD on the desktop front, and the new GRsecurity and ACL features will be a real competitor for the *BSD family. It will be most fascinating to see how things turn out. I wish the best to both of them, and I use both of them every day.

Re:Schedulers. (*nix v. win2k)

[Sivar]

Not needed. Linux and FreeBSD both handle different priority levels quite nicely, and in fact can handle them in a much more fine-grained fashion. NT actually has additional priority levels in-between each that you described above, but Linux and BSD have a total of 41 possible priority values (from -20 to 20, including zero)
If you set an application to a priority of 20, it isn't going to be bothering any other processes, and if you set an application to -20, it is going to be worshipped like a god by the scheduler.
As far as I know, neither have a real-time scheduling mode like NT, which is actually a good thing in many cases. If a program running at real-time priority goes into an infinite loop, or for any reason uses 100% of hte CPU (SETI@Home, for example) than the system is locked the hell up. Even the mouse will not get any time for cursor movement, and you have to reset the machine.

Read "man nice", "man renice", and probably "man top" (which I use to change priorities of running processes as root)

Re:Schedulers. (*nix v. win2k)

[Ded Bob]

Is there any reason why something like this isn't implemented in Linux or FreeBSD?

FreeBSD does have something like this: idle, normal, and real time. By default it is normal, but you can change it to idle (idprio(1)) or real time (rtprio(1)).

In the man page for rtprio(1) is one relevant bug:
"Under FreeBSD system calls are currently never preempted, therefore non-realtime processes can starve realtime processes, or idletime processes can starve normal priority processes."

Maybe the new scheduler will fix this?

Re:Schedulers. (*nix v. win2k)

[Nevyn]

Not needed. Linux and FreeBSD both handle different priority levels quite nicely, and in fact can handle them in a much more fine-grained fashion. NT actually has additional priority levels in-between each that you described above, but Linux and BSD have a total of 41 possible priority values (from -20 to 20, including zero)

Actually they can have much more than that, but the "user" can only set those 41 values. There isn't even a definition of how they have to map (so for instance you can have the schedular have priorities -20 to 20 including zero but in 0.5 increments. Or just -40 to 40 in 1.0 increments etc.

As far as I know, neither have a real-time scheduling mode like NT, which is actually a good thing in many cases. If a program running at real-time priority goes into an infinite loop, or for any reason uses 100% of hte CPU (SETI@Home, for example) than the system is locked the hell up. Even the mouse will not get any time for cursor movement, and you have to reset the machine.

Do "man sched_setparam" and man "setpriority" to learn about "real time" processes. Linux also had patches for SCHED_IDLE at one point, but that can cause pretty bad reasource deadlocks without priority inversion and so was never integrated.

There can be problems if your "real time" process misbehaves but then don't do that.

NOTE: The term "real time" is used to mean best effort at real time, for true real time you don't use a general purpose OS (Ie. NT doesn't count either).

Here is a great reason to prefer BSD

[sawilson]

http://uptime.netcraft.com/up/today/top.avg.html

You'll notice that 45 of those top 50 are BSD
machines. Of those 45, 19 are FreeBSD boxes.
You'll notice 1 Linux box. It's nice to see that
leading industry sites like bongload.com and
twobigirls.com have benefited so much from the
stability of BSD.

I use Linux AND FreeBSD

[leereyno]

Right now I've got four systems running Linux (RH-7.3 and 7.2) and one system running FreeBSD 4.6. At times in the past I've run OpenBSD and NetBSD as well.

I can tell you firsthand that in terms of system stability that Linux and FreeBSD are comparable if not indistinguishable. FreeBSD does seem to be more efficient however. The pentium 200 that I have FreeBSD on loads up KDE 3.0 noticably faster than Redhat 7.2 did, and once loaded it is more responsive. On older hardware FreeBSD definitely seems to have an advantage. I consider FreeBSD to be a very fast and well designed operating system. I keep trying to find places where using it instead of Linux would be an advantage.

Not everything about it is all that rosey however. The features and abilities that Linux provides but FreeBSD lacks such as SMP, kernel pre-emption, fast journaling filesystems, certain commerical software packages, 3D acclerated X servers, and generally better device support, make actually using FreeBSD as anything but an interesting toy kind of difficult to justify in many situations.

I worry about FreeBSD. I'd love to see it grow and progress not as a competitor to Linux, but as something of a companion to it. So many people just don't seem to realize that open source isn't about operating systems alone. What Linux and FreeBSD do is provide a foundation, they aren't the whole house. Both provide a powerful and stable platform for running the actual programs that people want to use in the first place. The future of open source development is going to be 90% apps and userland and 10% OS. To have religious and political wars over the OS portion is immature and counterproductive. Linux and FreeBSD aren't genuine competitors from an economic standpoint because it is the applications that both run that make either compelling in the first place.

I want BOTH Linux and FreeBSD to do well, to grow and expand and be the best operating systems anyone has ever seen. I detest the infantile immaturity of those who seek to create division and conflict between FreeBSD and Linux that simply shouldn't be there. I've gotten flames from FreeBSD "advocates" in particular filled with such hatred and obvious zealousness that you'd think they were Mac freaks, all because I described FreeBSD in terms that weren't favorable enough for their religious views. The Linux crowd is full of just as many jackasses, if not more.

Computer enthusiasts are known for generally having high IQ's. Unfortunately our reputation for having low EQ's is equally well earned. There are far too many borderline autistics and asperger's sufferers among us with severely retarded social skills. That is really the only explanation I can come up with when grown men with extensive vocabularies use them to throw a fit on par with that of an eight year old.

Anyway I'm drifting way off from what I wanted to write about. The point that I really want to make is that BOTH Linux and FreeBSD are absolutely fabulous operating systems (save the linux is just a kernel messages for church). The goals and vision behind each are so similar that any ill will between them is manufactured by immature, short sighted assholes. Microsoft is the enemy, not those who prefer another free Unix derivative that runs Mozilla, gnome, kde, etc just as well if not better than what someone else is using.

Lee