From: "Pradeep" <pradeep.annavarapu@moschip.com>
To: Rick Brown <rick.brown.3@gmail.com>
Cc: kernelnewbies <kernelnewbies@nl.linux.org>,
linux newbie <linux-newbie@vger.kernel.org>
Subject: Re: Why is Linux not RTOS?
Date: Thu, 5 Apr 2007 12:44:18 +0530 [thread overview]
Message-ID: <024901c77752$06e6a170$59c8a8c0@SAGGITARIUS> (raw)
In-Reply-To: 7783925d0704040521q3755394uf774884b5298eec2@mail.gmail.com
> Hi,
>
> Why is Linux kernel considered a (hard) realtime OS? I already
Linux kernel is never considered a real time OS.
A real time OS should be predictable.The general linux kernel is not
predictable because of many reasons.
A few are it uses virtual memory. when there is virtual memory there will be
page swaps which are un predictable.
And the linux scheduler is not a deterministic one.
There is a scheduler project which provides a deternistic behaviour to the
scheduler.This scheduler is called O(1) scheduler.
This gives a constant scheduling latency. This is used in many embedded
linux to make it a real time OS. Ex: motavista
> understand the basic reason is that the linux kernel does not
> guarantee that a task will be completed on time. But I would
> appreciate answers in terms of more of kernel jargons.
>
> What stops us from classifying kernel as hard RTOS? Is it because at
An RTOS is just a facilitator to build Real time systems. A Real time system
developer should analyse a RTOS wether is will be useful for his system.
If some body is holding spin lock and making it non-preemptive its a bad
design. So even a RTOS linux has spin locks. Its the designer who should
take care.
> times the kernel is non-preemptive (for e.g. while holding spinlocks)?
> Has it got something to do with interrupt latency / scheduling latency
> etc?
>
> Is the behaviour of the kernel (when it is preemptive) similar to hard
> real time OS ??
>
> Thanks,
>
> Rick
> -
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next prev parent reply other threads:[~2007-04-05 7:14 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-04-04 12:21 Why is Linux not RTOS? Rick Brown
2007-04-04 13:00 ` John Anthony Kazos Jr.
2007-04-04 13:05 ` Rick Brown
2007-04-04 15:21 ` Daniel Cheng
2007-04-05 9:36 ` Tzahi Fadida
2007-04-05 10:05 ` sandeep lahane
2007-04-05 10:11 ` Raseel Bhagat
2007-04-05 10:23 ` sandeep lahane
2007-04-05 13:28 ` Mark Hounschell
2007-04-05 10:07 ` Raseel Bhagat
2007-05-30 0:47 ` Rodrigo Rubira Branco
2007-05-31 1:16 ` K.R. Foley
2007-04-05 7:14 ` Pradeep [this message]
2007-04-05 9:01 ` Raseel Bhagat
2007-04-05 9:05 ` Pharaoh .
2007-04-05 11:52 ` Not Initialize the shrinker->list after kmalloc() in mm/vmscan.c(V2.6.12)? qingxiaoming
2007-04-09 5:57 ` Rajat Jain
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