OSNews: http://www.osnews.com/story/22938/New_Version_of_SCHED_DEADLINE_for_Linux_Available Exploring the Future of Computing en-us Copyright 2001-2013, David Adams adam+nospam@osnews.com Sat, 25 May 2013 16:23:02 GMT http://www.osnews.com/images/osnews.gif OSNews.com http://www.osnews.com Just what is needed http://www.osnews.com/thread?411540 http://www.osnews.com/thread?411540 Just what Linux needs, yet another scheduler. Oh well. Mon, 01 Mar 2010 11:48:00 GMT donotreply@osnews.com (strcpy) Comments RE: Just what is needed http://www.osnews.com/thread?411546 http://www.osnews.com/thread?411546
Just what Linux needs, yet another scheduler. Oh well.


af far as i care they could well add not even one, but some hundred more scheduling classes, if at least one among them can let linux catch up with recent realtime OS reasearch - it's been years since i read publications about deadline monotonic scheduling for HARD realtime systems, and it wasn't "new" stuff even at the time...

hard realtime tasks don't just require timely activation and shortest schedule-in latencies - they need to be able to rely on system calls they invoke, taking deterministic times to execute - without this, they cannot guarantee temporally correct behaviour (which is the essence of real time computing), no matter the scheduling classes

so the point is, what does linux do to ensure that code paths for IO operations, enumeration of processes or files in a directory, or *whatever*, run in a constant, or at least upper bound, time?Edited 2010-03-01 13:54 UTC Mon, 01 Mar 2010 13:53:00 GMT donotreply@osnews.com (silix) Comments RE[2]: Just what is needed http://www.osnews.com/thread?411635 http://www.osnews.com/thread?411635 You do know that the realtime code in Linux main mostly comes in junks and pieces from existing real time Linux projects ? It's not like Linux not already does this, but it just takes time to make it more generic and suitable for general consumption. Mon, 01 Mar 2010 21:51:00 GMT donotreply@osnews.com (Lennie) Comments RE[3]: Just what is needed http://www.osnews.com/thread?411663 http://www.osnews.com/thread?411663
You do know that the realtime code in Linux main mostly comes in junks and pieces from existing real time Linux projects ?

yes, i know - but i'm not interested in a particular variant or branch or distribution, thus when i said "what does linux do to..." i actually meant "what is being done in the linux ecosystem to..."
i didnt make myself clear, my fault

It's not like Linux not already does this

so you'll be able to point me to paper in which the "syscall execution time" problem is analysed, and solutions are detailed, which is what i asked earlier :-)

but it just takes time to make it more generic and suitable for general consumption.

it would be nice to define "general consumption" -
in reality, hard real time is something that belongs to critical systems devoted to specific tasks for which a specific software solution is holistically tailored and deployed
that HRT is needed for MP3's and movies to play without stuttering is a common misconception - the most renowned multimedia prone desktop operating system (the BeOS) was not a real time OS, and many multimedia application are implemented as normal event loops (calculating delta's between the current and a previous timestamp to , e.g. calculate the frames needed for the animation to appear fluid, but not so much relying on system call nominal execution times)

desktop users don't actually need HRt, they don't need to be able to run tasks at higher priority than the kernel itself (which is what a soft real time kernel mostly does), they need what they need is responsiveness, and responsiveness can be achieved via other means, like prioritizing interactive tasks at the IO operation (not just scheduling) level, and /or optimising local IPC (that between applications and the graphic server, for instance) with more efficient mechanisms than sockets (LRPC or doors, that other Os's have had for years, but linux lacks, being born as a server OS) or even basic functionality like handoff scheduling (needed to shorten and make more deterministic ipc latency, and that linux AFAIK doesn't have yet) Mon, 01 Mar 2010 23:43:00 GMT donotreply@osnews.com (silix) Comments RE[4]: Just what is needed http://www.osnews.com/thread?412289 http://www.osnews.com/thread?412289 With general consumption I just mean, the people working on mainline don't mind maintaining it. It can be added to mainline and less code is needed for 'fringe' cases, like some kind of embedded devices. Fri, 05 Mar 2010 00:40:00 GMT donotreply@osnews.com (Lennie) Comments