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	Light Weight Kernel Threads - Wikipedia, the free encyclopedia
		Light Weight Kernel Threads or LWKT is a term from computer science in general and in DragonFlyBSD in particular.
		LWKTs differ from normal kernel threads in that they can preempt normal kernel threads.
		It uses a fixed priority scheme but you have to keep in mind that the fixed priorities are differentiating major subsystems, not user processes.
	en.wikipedia.org /wiki/LWKT (202 words)

	DragonFly BSD - Wikipedia, the free encyclopedia
		One advantage to this clean compartmentalization of the threading subsystem is that the processors' on-board caches in SMP systems do not contain duplicated data, allowing for higher performance by giving each processor in the system the ability to use its own cache to store different things to work on.
		The LWKT subsystem is being employed to partition work among multiple kernel threads (for example in the networking code; one thread per protocol), reducing contention by removing the need to share certain resources among various kernel tasks.
		Much of the system's core including the LWKT subsystem, the IPI messaging subsystem and the new kernel memory allocator among other things are lockless, meaning that they work without using mutexes, and operate on a per-CPU basis.
	www.wikipedia.org /wiki/DragonFlyBSD (2598 words)

	Glossary of Terms - DFWiki (Site not responding. Last check: 2007-11-03)
		The LWKT scheduler only applies its scheduling decisions to the kernel and is independent from the userland 4.4BSD scheduler.
		LWKT has a fully MP clean API and allows turning off the BGL on a thread-by-thread basis; this fits with the goal of threading the subsystems in the kernel and provides a clear and straight-forward path to taking subsystems out from under the BGL.
		LWKT facilities are implemented in src/sys/kern/lwkt_*.c; notably, lwkt_thread.c (http://www.dragonflybsd.org/cgi-bin/cvsweb.cgi/~checkout~/src/sys/kern/lwkt_thread.c), lwkt_msgport.c (http://www.dragonflybsd.org/cgi-bin/cvsweb.cgi/~checkout~/src/sys/kern/lwkt_msgport.c), and lwkt_token.c (http://www.dragonflybsd.org/cgi-bin/cvsweb.cgi/~checkout~/src/sys/kern/lwkt_token.c).
	wiki.dragonflybsd.org /index.php/Glossary_of_Terms (542 words)

	sys/kern/lwkt_thread.c (Site not responding. Last check: 2007-11-03)
		User process scheduling is a totally 433 * different beast and LWKT priorities should not be confused with 434 * user process priorities.
		This code assumes that the MP lock is held for 964 * the tdallq operation and that the thread has been descheduled from its 965 * original cpu.
		We also have to wait for the thread to be entirely switched 966 * out on its original cpu (this is usually fast enough that we never loop) 967 * since the LWKT system does not have to hold the MP lock while switching 968 * and the target may have released it before switching.
	fxr.watson.org /fxr/source/kern/lwkt_thread.c?v=DFBSD (3402 words)

	Light Weight Kernel Threads (Site not responding. Last check: 2007-11-03)
		LWKT means "Light Weight Kernel Threads" in science in general and in DragonFly BSD in particular.
		LWKTs differ from normal threads in that they can preempt normal threads.
		LWKT interrupt thread can preempt most other for example.
	www.freeglossary.com /LWKT (620 words)

	Serializing tokens - Wikipedia, the free encyclopedia
		Concurrent Execution: In multiprocessor computers, your thread may also be run at exactly the same time as another thread on a different CPU.
		Preemption: A thread may be preempted by a higher priority thread, such as a hardware interrupt or LWKT.
		Voluntary Blocking: A thread may voluntarily block (aka "go to sleep") if it has to wait for something, has no work to do, or calls a function that blocks-- note that even the call to acquire a lock can block.
	en.wikipedia.org /wiki/Serializing_tokens (782 words)

	DragonFly - Light Weight Kernel Threading Model
		The LWKT model has a number of key features that can be counted on no matter the architecture.
		Any LWKT scheduling operation on a particular cpu is only directly executed on that cpu.
		IPI messaging is used heavily by at least half a dozen major LWKT subsystems, including the per-cpu thread scheduler, the slab allocator, and messaging subsystems.
	www.dragonflybsd.org /goals/threads.cgi (1212 words)

	ONLamp.com: Behind DragonFly BSD
		IMHO, I believe LWKT to be a far superior environment for SMP (and UP as well) over the traditional process model that the other BSDs use and over the mutex-centric model that FreeBSD-5 uses.
		LWKT provides an extremely efficient and scaleable programming environment on both UP and SMP systems.
		DragonFly does not try to schedule specifically for the hyperthreading case but LWKT does a pretty good job and we are at least on par with FreeBSD.
	www.onlamp.com /pub/a/bsd/2004/07/08/dragonfly_bsd_interview.html?page=2 (1935 words)

	CVS log for src/sys/kern/lwkt_msgport.c
		Thus the target is always guarenteed to see the original message and then a second, abort message (the same message with ms_cmd = ms_abort) regardless of whether the abort was requested before or after the target retrieved the original message.
		This is a major cleanup of the LWKT message port code.
		Messages are sent to message ports and typically replied to a message port embedded in the originating thread's thread structure (td_msgport).
	dragonflybsd.org /cgi-bin/cvsweb.cgi/src/sys/kern/lwkt_msgport.c?... (3321 words)

	Mike's Weblog (Site not responding. Last check: 2007-11-03)
		The LWKT scheduler guarantees that a running thread is not preempted by any other thread holding the same serializing token.
		If a thread blocks or yields (= giving up it’s time-slice), then the LWKT scheduler is allowed to run a thread that has a serializing token in common with the blocking or yielding thread (or one with no token in common).
		Thus, when a thread blocks or yields, it automatically leaves it’s critical section until it is running again, and it is responsible for all possible harm that may result due to leaving the critical section.
	www.ntecs.de /blog/2004/7/20 (424 words)

	Add new comment
		In response to a question raised on the dragonfly-kernel mailing-list, Matt Dillon [interview] gives an overview of plans to revise the DragonFly userland scheduler, the second of two schedulers that Dragonfly currently utilizes in a layered fashion.
		there's the LWKT scheduler, which is as close to perfect as its possible to be, and there is the userland scheduler, which is the one that needs work.".
		LWKT itself uses a strict fixed priority model and round-robins tasks
	kerneltrap.org /comment/reply/4370 (1289 words)

	DragonFly BSD - Wikipédia
		Cela pose, aux yeux de Matt Dillon de nombreux problèmes de complexité, rendant le code difficile à maintenir, et de performance.
		LWKT, annoncé officiellement sur les mailing-listes FreeBSD, constitue un système puissant d'échange de messages entre les threads légers noyau, leur permettant de coopérer efficacement.
		Dans ce dernier, elle utiliserait alors LWKT, et permettrait de supporter des systèmes de fichiers en espace utilisateur (« userspace »).
	fr.wikipedia.org /wiki/DragonFly_BSD (363 words)

	HT program (Site not responding. Last check: 2007-11-03)
		Not quite The LWKT stands for the "Leifsson White-Key Temperament" which I "devised" in my early tuning studies.
		I tuned the white keys of the temperament, went for a coffee break, came back forgetting the sharps and took surprisingly long to figure out what was wrong after tuning a few octaves :-) Needless to say, this temperament offers a whole new spectrum of shades and nuances individual to each piano.
		I´ve been trying to get you people to ask about this for some time, I needed to have an excuse to bring it up.
	www.ptg.org /pipermail/pianotech/2000-October/072311.html (185 words)

	OSNews.com
		As seen on kerneltrap.org: "In response to a question raised on the dragonfly-kernel mailing-list, Matt Dillon gives an overview of plans to revise the DragonFly userland scheduler, the second of two schedulers that Dragonfly currently utilizes in a layered fashion.
		"LWKT itself uses a strict fixed priority model and round-robins tasks running at the same priority.
		So LWKT is not directly comparable to Linux's scheduler.
	www.osnews.com /comment.php?news_id=9142 (1593 words)

	[No title] (Site not responding. Last check: 2007-11-03)
		The reality is that for most tokens you won't block for long, but if it is critical that you not block in a particular section of code then you have to use the other major programming abstraction in DragonFly, which is the per-cpu globaldata mechanism and LWKT (light weight kernel threading) mechanism.
		Many subsystems in DragonFly do not need tokens, mutexes, or locks of any kind because they are built ground-up to be MP friendly.
		For example, the LWKT scheduler does not require locks or tokens of any sort, and it only messes with the Big Giant Lock on behalf of the thread it is trying to switch to, not because it needs it itself (it doesn't).
	cache.gmane.org /gmane/os/dragonfly-bsd/kernel/4212 (574 words)

	HT program
		You have built something that you truly and honestly believe has great quality to it, and you have the technical capability of showing it.
		You agree to come over here to the seminar and present your EBVT and perhaps I´ll agree to present the oh so highly diversified LWKT.
		I have no idea what LWKT stands for.
	www.ptg.org /pipermail/pianotech/2000-October/072295.html (1417 words)

	Re: sending messages, user process <--> kernel module
		A Linux kernel project I'm working on does it using signals, but is seems like such a dirty hack to me. lwkt will be much cleaner, especially for something like a userspace hotplug/devfs daemon.
		> :according to the lwkt_ prefix it is not intended.
		> : > :~ibotty > > The answer is yes, the intention of the LWKT syscall messaging is to > be able to do this.
	www.sanskrit.ru /dragonflybsd/kernel/msg00750.html (249 words)

	Rio Girls Online - Join Now (Site not responding. Last check: 2007-11-03)
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		dfhs ldkh gslkdgh sldkg sldkhg lwkt wlket wlekth wlekht
	victor.ludost.net /adult/sites/rio_girls_online/members.html (281 words)

	CVS log for src/sys/sys/param.h
		Userland reschedules are requested when a process is scheduled with a higher priority then the currently running process, and LWKT reschedules are requested when a thread is scheduled with a higher priority then the currently running thread.
		We were previously also testing the LWKT run queue for higher priority threads, but this was causing inefficient scheduler interactions when two processes are doing tightly bound synchronous IPC (e.g.
		The priority was a user scheduler thingy that is not used by the LWKT subsystem.
	dragonflybsd.org /cvsweb/src/sys/sys/param.h (2721 words)

	webrover.de :: lwkt (Site not responding. Last check: 2007-11-03)
		Mögliche Themen : FreeBSD - LWKT - Implement - This - Hiten - David - Move - June - performance - DragonFly - subsystems - interrupts
		lwkt, dfports, the live cd, amd64 work, and much more, including coordination on projects other contributors have submitted.
		lwkt) system that is separate from the dynamic userland scheduler, a fine-grained system timer abstraction for kernel use, a fully integrated light weight messaging system, and a core ipi (inter processor interrupts) messaging system for inter-processor communications.
	www.webrover.de /cgi-bin/s.pl?q=LWKT (196 words)

	sys/kern/lwkt_caps.c (Site not responding. Last check: 2007-11-03)
		This API 41 * is known as the CAPS interface.
		42 * 43 * Generally speaking this module abstracts the LWKT message port interface 44 * into userland Clients and Servers rendezvous through ports named 45 * by or wildcarded by (name,uid,gid).
		The kernel provides system calls 46 * which may be assigned to the mp_* fields in a userland-supplied 47 * kernel-managed port, and a registration interface which associates an 48 * upcall with a userland port.
	fxr.watson.org /fxr/source/kern/lwkt_caps.c?v=DFBSD (1413 words)

	IRC Log
		Many of the goals are rather incompatible with the direction FreeBSD-5 is going, LWKT being the most obvious one and the messaging we intend to do coming in a close second.
		Threads do not migrate between cpus preemptively, so the per-cpu data structure can be accessed without any mutexes or locks, and the LWKT scheduler can operate without any mutexes or locks (just a critical section to protect from interrupts on that cpu).
		DragonFly's userland scheduler is protected by the Giant lock at the moment, but the key point is that it is a different scheduler from the LWKT scheduler.
	www.slashnet.org /forums/DragonflyBSD-20031009.html (5492 words)

	DragonFly - End of Year Summary for 2003 (Site not responding. Last check: 2007-11-03)
		Matt Dillon created a local override of the existing FreeBSD ports system, to allow port installation until a DragonFly-native solution is created.
		This is a library that allows userland threading, similar to the existing LWKT.
		LWKT gives each CPU in the system its own scheduler, and threads are locked to that CPU.
	wids.net /www.dragonflybsd.org/ja/status/report-2003.cgi (1020 words)

	[No title]
		The LWKT module - * uses smp_active to optimize UP builds and to avoid sending IPIs during - * early boot (primarily interrupt and network thread initialization).
		On SMP machines + * smp_active_mask is 1 prior to SMP activation, then it is a mask of all + * available cpus.
		The LWKT module uses smp_active_mask to optimize UP + * builds and to avoid sending IPIs during early boot (primarily interrupt + * and network thread initialization).
	apollo.backplane.com /DFlyMisc/cpusync01.patch (1443 words)

	Re: LWPs and LWKTs, how they relate
		Of course there still will be LWKTs that don't have any LWP
		attached lwkt being one of the most important things).
		So it is: proc 1 <-> lwp 1 <-> lwkt 1 [single threaded] proc 2 <-> lwp 2 <-> lwkt 2 [multi threaded] \> lwp 3 <-> lwkt 3 lwkt 4 [kernel thread] One proc groups multiple "threads" called struct lwp.
	www.mail-archive.com /kernel@crater.dragonflybsd.org/msg00485.html (316 words)

	Gmane -- Mail To News And Back Again (Site not responding. Last check: 2007-11-03)
		As you might know, I've been meaning to get OpenBSD into the SMP realm, and to have better SMP support.
		I've had my eye on your little project for a while, and I must say that your LWKT ideas, and XIO seem very interesting.
		So, if any of you would like to get funded for getting this into OpenBSD, just drop me a line, and I'll see what I can arrange.
	article.gmane.org /gmane.os.dragonfly-bsd.kernel/4207 (116 words)

	[No title] (Site not responding. Last check: 2007-11-03)
		The LWKT subsystem switches while holding a critical * section and we maintain that abstraction here (e.g.
		Also use this opportunity + * to lazy-raise our LWKT priority.
		If we ever support an emulation where this + * is not the case, this code will need to be revisited.
	eirikn.kerneled.org /dragonfly/sysmsg-050804.diff (1387 words)

	Gmane -- Mail To News And Back Again (Site not responding. Last check: 2007-11-03)
		Henceforth, I will try to put your LWKT and XIO technology :into OpenBSD, because it seems the right thing to do.
		I think the LWKT technology and approach is the way to go (at least compared to FreeBSD-5's model).
		It's a much saner programming model to be sure.
	article.gmane.org /gmane.os.dragonfly-bsd.kernel/4214 (276 words)

	Manual for sleep - man 9 sleep (Site not responding. Last check: 2007-11-03)
		If flags contains the PCATCH flag, signals are checked before and after sleeping, else signals are ignored.
		IMPLEMENTATION NOTES Unlike FreeBSD, the tsleep() function in DragonFly ignores priority information because it is not required by the LWKT subsystem.
		Sleeps without the P_SINTR flag set are assumed to be disk-waits, otherwise they are normal sleeps.
	tautology.org /software/man/9/sleep (414 words)

	Annoucning DragonFly BSD! (Site not responding. Last check: 2007-11-03)
		This proving work involved implementing much of the earlier UP->SMP converstion work that was done when 5.x first branched, but under an entirely new mutex-free light weight kernel threading infrastructure.
		It includes the LWKT system, interrupt threads, and pure threads for system processes amoung other things.
		For obvious reasons the codebase will only run on i386 for now, and ports to other platforms will not happen until the MD infrastructure is cleaned up and finalized.
	lists.freebsd.org /pipermail/freebsd-current/2003-July/006889.html (440 words)

	Unix - DragonFly-1.0 (1 CD's) en DeRemate.com.ar
		We have replaced nearly all of the core threading, process, interrupt, and network infrastructure with DragonFly native subsystems.
		We have our own MP-friendly slab allocator, a Light Weight Kernel Threading (LWKT) system that is separate from the dynamic userland scheduler, a fine-grained system timer abstraction for kernel use, a fully integrated light weight messaging system, and a core IPI (Inter Processor Interrupts) messaging system for inter-processor communications.
		We have managed to retain 4.x's vaunted stability throughout the development process, despite ripping out and replacing major subsystems, and we have a demonstratively superior coding model which is both UP (Uni-Processor) and MP (Multi-Processor) friendly and which is nearly as efficient on UP systems as the original 4.x UP-centric code is on UP systems.
	www.deremate.com.ar /Afiliados/Tracking.asp?SiteID=8039552&idu=2019235&UrlTo=http://www.deremate.com.ar/accdb/ViewItem.asp?IDI=8052888&IDCamino=564 (737 words)

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