Light Weight Kernel Threads (original) (raw)
Light Weight Kernel Threads (LWKT) is a computer science term and from DragonFlyBSD in particular. LWKTs differ from normal kernel threads in that they can preempt normal kernel threads. According to Matt Dillon, DragonFlyBSD creator: The mainframe z/OS Operating system supports a similar mechanism, called SRB (Service Request Block). In UNIX, "kernel threads" have two threads, one is the core thread, one is the user thread.
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| dbo:abstract | Light Weight Kernel Threads (LWKT) is a computer science term and from DragonFlyBSD in particular. LWKTs differ from normal kernel threads in that they can preempt normal kernel threads. According to Matt Dillon, DragonFlyBSD creator: The LWKT scheduler is responsible for actually running a thread. It uses a fixed priority scheme, but the fixed priorities are differentiating major subsystems, not user processes. For example, hardware interrupt threads have the highest priority, followed by software interrupts, kernel-only threads, then finally user threads. A user thread either runs at user-kernel priority (when it is actually running in the kernel, e.g. running a syscall on behalf of userland), or a user thread runs at user priority. DragonFly does preempt, it just does it very carefully and only under particular circumstances. An LWKT interrupt thread can preempt most other threads, for example. This mimics what FreeBSD-4.x already did with its spl/run-interrupt-in-context-of-current-process mechanism. What DragonFly does *NOT* do is allow a non-interrupt kernel thread to preempt another non-interrupt kernel thread. The mainframe z/OS Operating system supports a similar mechanism, called SRB (Service Request Block). SRB's represent requests to execute a system service routine. SRB's are typically created when one address space detects an event that affects a different address space; they provide one of several mechanisms for asynchronous inter-address space communication for programs running on z/OS. An SRB is similar to a Process Control Block (PCB), in that it identifies a unit of work to the system. Unlike a PCB, an SRB cannot "own" storage areas. In a multiprocessor environment, the SRB routine, after being scheduled, can be dispatched on another processor and can run concurrently with the scheduling program. The scheduling program can continue to do other processing in parallel with the SRB routine. Only programs running in kernel mode can create an SRB. The Windows Operating System knows a similar light weight thread mechanism named "fibers". Fibers are scheduled by an application program. The port of the CICS Transaction Server to the Windows platform uses fibers, somewhat analogous to the use of "enclaves" under z/OS. In UNIX, "kernel threads" have two threads, one is the core thread, one is the user thread. (en) 軽量カーネルスレッド (英: Light Weight Kernel Threads) あるいは LWKT とは、計算機科学の一般的な用語であり、カーネルスレッドの一種、また特にDragonFly BSD固有の実装のことを指す。 LWKTは、カーネルスレッドをプリエンプトできるという点において、通常のカーネルスレッドとは異なる。 DragonFlyBSDの開発者Matt Dillonによれば、DragonFlyBSDのLWKTは以下のような特性を持つ。 "LWKTスケジューラはスレッドの実行に責任を持ち、固定優先度のスケジュール方法を採用しているが、固定優先度はユーザープロセスではなく主要なサブシステム間を優先度付けすることに注意してほしい。"たとえば、ハードウェアの割り込みスレッドは最も高い優先度を持っており、次がソフトウェア割り込み、カーネル内部のスレッド、最後がユーザースレッドになっている。ユーザースレッドはユーザー-カーネル優先度(カーネル内コードの実行、たとえばシステムコールの一部をユーザーランドで実行するような場合)あるいはユーザー優先度で動作する。 "DragonFlyはプリエンプトを行うが、特別な状況下でのみ非常に注意深く行う。LWKTの割り込みスレッドは他の大半のスレッドをプリエンプトすることができる。これはFreeBSD-4.xにおける割り込み優先レベル(SPL)/現在プロセスでの割り込み実行の動きを模倣したものだが、DragonFlyでは非割り込みカーネルスレッドが他の非割り込みカーネルスレッドをプリエンプトしない[1]。 (ja) |
| dbo:wikiPageExternalLink | http://www.dcbsdcon.org/speakers/slides/luciani_dcbsdcon2009.pdf http://www.kerneltrap.org/node/14116 http://www.osnews.com/story.php%3Fnews_id=6338 http://www.osnews.com/story/13352/A_Quick_Review_of_DragonFly_BSD_1_4 http://www.onlamp.com/pub/a/bsd/2004/07/08/dragonfly_bsd_interview.html http://leaf.dragonflybsd.org/mailarchive/kernel/2003-11/msg00321.html http://hup.hu/node/4512 https://web.archive.org/web/20101223004617/http:/www.dcbsdcon.org/speakers/slides/luciani_dcbsdcon2009.pdf https://web.archive.org/web/20110515101806/http:/kerneltrap.org/node/14116 https://lwn.net/Articles/384200/ http://www.internetnews.com/dev-news/article.php/3576426 http://www.internetnews.com/dev-news/article.php/3622406 |
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| rdfs:comment | Light Weight Kernel Threads (LWKT) is a computer science term and from DragonFlyBSD in particular. LWKTs differ from normal kernel threads in that they can preempt normal kernel threads. According to Matt Dillon, DragonFlyBSD creator: The mainframe z/OS Operating system supports a similar mechanism, called SRB (Service Request Block). In UNIX, "kernel threads" have two threads, one is the core thread, one is the user thread. (en) 軽量カーネルスレッド (英: Light Weight Kernel Threads) あるいは LWKT とは、計算機科学の一般的な用語であり、カーネルスレッドの一種、また特にDragonFly BSD固有の実装のことを指す。 LWKTは、カーネルスレッドをプリエンプトできるという点において、通常のカーネルスレッドとは異なる。 DragonFlyBSDの開発者Matt Dillonによれば、DragonFlyBSDのLWKTは以下のような特性を持つ。 "LWKTスケジューラはスレッドの実行に責任を持ち、固定優先度のスケジュール方法を採用しているが、固定優先度はユーザープロセスではなく主要なサブシステム間を優先度付けすることに注意してほしい。"たとえば、ハードウェアの割り込みスレッドは最も高い優先度を持っており、次がソフトウェア割り込み、カーネル内部のスレッド、最後がユーザースレッドになっている。ユーザースレッドはユーザー-カーネル優先度(カーネル内コードの実行、たとえばシステムコールの一部をユーザーランドで実行するような場合)あるいはユーザー優先度で動作する。 (ja) |
| rdfs:label | Light Weight Kernel Threads (en) 軽量カーネルスレッド (ja) |
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