BOUNCE rtl@rtlinux.org: Approval required: (fwd)

[Der Herr Hofrat <der.herr@hofr.at>]

>From owner-rtl Sun May 20 02:31:22 2001
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From: Der Herr Hofrat <der.herr@hofr.at>
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Subject: Re: [rtl] RTL and linux system calls
In-Reply-To: <F272XLsxpTljBOh8s4K0000d2bb@hotmail.com> from daniel sheltraw at
 "May 20, 2001 02:43:19 am"
To: rtl@fsmlabs.com
Date: Sun, 20 May 2001 09:28:45 +0200 (CEST)
CC: rtl@rtlinux.org
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> Hell RTers
> 
> I found the following paragraph at 
> http://www.mysreenu.com/linux_software_design.html.
> Would someone please tell me whether the last sentence is correct. It was my 
> understanding that anything running under Linux could be prempted by a RT 
> scheduled task under RTLinux.
> 
> Thanks,
> Daniel
> 
> "Even with RTLinux/RTAI, it is generally the case that a real-time
> application will have tasks executing within user space. The issue then
> becomes the reliability of their performance. The behavior of all userspace 
> programs, including daemons, may be important. In particular, if any user 
> task other than your time-critical real-time task is making system calls, 
> then that may delay your task."

that wrong - the user-space app can be delayed - and you could force priority inversion by using badly designed synchronization between the RT-Task and the non-RT-task but if the non-RT side does system calls that is irrelevant for RT-performance. So as long as all time-critical steps are performed in the RT-modules you are safe - any non-RT , and that is what this article is probably refering to as "weil have tasks executing in user space" , like front end GUI's, may be delayed indefinetly (atleast in theory).

this is true for RTL and RTAI so who ever wrote that article did not read the basic docs of either.

hofrat