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On 09/05/2012 09:38 AM, Tom Smith wrote:
<blockquote
cite="mid:CAPzmA6dmdWeZXxXKtmypmrMi+ZnbTr=3CwpmnwDqXA8Q26gPNg@mail.gmail.com"
type="cite">
<div>hi joel</div>
<div> </div>
<div>Glad to receive an email from you. To me, you are the God of
RTEMS world. :)</div>
</blockquote>
:) <blush><br>
<blockquote
cite="mid:CAPzmA6dmdWeZXxXKtmypmrMi+ZnbTr=3CwpmnwDqXA8Q26gPNg@mail.gmail.com"
type="cite">
<div> </div>
<div>For me, it is totally ok to use the discussion as a
supplement to that section in manual.<br>
I think gedare's attitude is more important, because gedare
provided the deep insight on this topic.</div>
<div> </div>
<div>For now, I think I am just new to RTEMS and not sufficient
to write some usefull material. But I am studying</div>
<div>an OS course from Internet, I will come up with a new
version of that section when I finished the scheduling chapters.</div>
<div> </div>
</blockquote>
This is a new section in the manual and a tough subject to discuss.
<br>
I really believe that each new user should feel free to ask
questions.<br>
Your first reading of the documentation will see things that RTEMS <br>
developers and more experienced users simply read around. After <br>
a certain point, we all see what we expect to see.<br>
<br>
Please make suggestions and corrections. RTEMS has a very wide <br>
user base with lots of differences in native language and
backgrounds. <br>
If the manual doesn't make something clear to you, then this is just<br>
your first opportunity to contribute. :)<br>
<br>
Plus explaining how to select the appropriate thread scheduling<br>
algorithm for your application is just hard.<br>
<br>
--joel<br>
<blockquote
cite="mid:CAPzmA6dmdWeZXxXKtmypmrMi+ZnbTr=3CwpmnwDqXA8Q26gPNg@mail.gmail.com"
type="cite">
<div>Best regards</div>
<div> </div>
<div>Tom</div>
<div> </div>
<div class="gmail_quote">2012/9/5 Joel Sherrill <span dir="ltr"><<a
moz-do-not-send="true"
href="mailto:joel.sherrill@oarcorp.com" target="_blank">joel.sherrill@oarcorp.com</a>></span><br>
<blockquote style="BORDER-LEFT:#ccc 1px solid;MARGIN:0px 0px 0px
0.8ex;PADDING-LEFT:1ex" class="gmail_quote">
<div bgcolor="#FFFFFF" text="#000000">Can any of this
discussion be used as material to enhance<br>
the section in the manual? This stuff is very hard to
explain.<br>
<br>
Tom .. any suggestions? Just emailing us a new version of<br>
the section would help. It is just a few paragraphs.
<div>
<div class="h5"><br>
<br>
On 09/05/2012 04:37 AM, Tom Smith wrote:
<blockquote type="cite">
<div><font color="#888888">hi Gedare</font><br>
</div>
<div>Thank you very much for the quick reply.</div>
<div> </div>
<div>The relationship between "processor utilization
rule" and "First Deadline Rule" you stated is clear
and wonderfull.</div>
<div> </div>
<div>I think I got your key point. But I still need to
read more to fully understand RMS. </div>
<div> </div>
<div>Anyhow, thank you very much</div>
<div> </div>
<div>tom</div>
<div> </div>
<div>2012/9/3 Gedare Bloom <span dir="ltr"><<a
moz-do-not-send="true"
href="mailto:gedare@rtems.org" target="_blank">gedare@rtems.org</a>></span><br>
</div>
<div class="gmail_quote">
<blockquote style="BORDER-LEFT:#ccc 1px
solid;MARGIN:0px 0px 0px 0.8ex;PADDING-LEFT:1ex"
class="gmail_quote">
<div>On Mon, Sep 3, 2012 at 8:27 AM, Tom Smith
<<a moz-do-not-send="true"
href="mailto:venture.g@gmail.com"
target="_blank">venture.g@gmail.com</a>>
wrote:<br>
> Hi everyone,<br>
><br>
> I am studying Chapter 19 "Rate Monotonic
Manager" of c_user.pdf, and I get<br>
> some questions<br>
><br>
> In c_user.pdf, it says<br>
><br>
> "For a given set of independent periodic
tasks, if each task meets its first<br>
> deadline when all<br>
> tasks are started at the same time, then
the deadlines will always be met<br>
> for any combination<br>
> of start times."<br>
><br>
> my question is that:<br>
> 1. If a set of independent periodic tasks
do not meet the "Processor<br>
> Utilization Rule", but they satisfy the
"First Deadline Rule", can they be<br>
> scheduled using RMS ?<br>
><br>
</div>
Yes; you may like to consult a handbook on
real-time systems for<br>
detailed explanations, but I'll make an effort
here. The processor<br>
utilization rule is a sufficient but not necessary
test for<br>
schedulability; some systems are schedulable that
do not satisfy the<br>
maximum processor utilization bounds. The "First
Deadline Rule" is a<br>
way to simplify the analysis of when tasks may
start by stating the<br>
worst-case scheduling window happens when all
tasks start at the same<br>
time; releasing all tasks at once ensures that
every task has a<br>
critical instant at the same time; this rule
coincides with the<br>
critical instance theorem. When you don't have
simultaneous release of<br>
tasks you cannot be certain when the critical
instance of a given task<br>
will occur, in which case you may need to compute
the entire<br>
hyperperiod; for non-harmonic task sets the
hyperperiod could be<br>
prohibitively large. (Harmonic periodic tasks are
typically quite easy<br>
to test for schedulability.)<br>
<div><br>
> 2. Is it necessary to start all tasks at
the same time in a real<br>
> application, or is it just a trick during
analysis phase?<br>
><br>
</div>
I suppose that depends how closely you want your
analysis to match<br>
your application. If you analyze with simultaneous
release but do not<br>
ensure that during execution then what have you
analyzed? You cannot<br>
be certain your application will meet its
deadlines anymore. In this<br>
case you should use a schedulability test that
does not require<br>
simultaneous release.<br>
<span><font color="#888888"><br>
-Gedare<br>
</font></span>
<div><br>
> any review on this point from anyone is
welcomed. So feel free to comment.<br>
> Best regards,<br>
><br>
> Tom Smith<br>
><br>
</div>
<div>
<div>>
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href="mailto:rtems-users@rtems.org"
target="_blank">rtems-users@rtems.org</a><br>
> <a moz-do-not-send="true"
href="http://www.rtems.org/mailman/listinfo/rtems-users"
target="_blank">http://www.rtems.org/mailman/listinfo/rtems-users</a><br>
><br>
</div>
</div>
</blockquote>
</div>
<br>
</blockquote>
<br>
<br>
</div>
</div>
<span class="HOEnZb"><font color="#888888">
<pre cols="72">--
Joel Sherrill, Ph.D. Director of Research& Development
<a moz-do-not-send="true" href="mailto:joel.sherrill@OARcorp.com" target="_blank">joel.sherrill@OARcorp.com</a> On-Line Applications Research
Ask me about RTEMS: a free RTOS Huntsville AL 35805
Support Available (256) 722-9985
</pre>
</font></span></div>
</blockquote>
</div>
<br>
</blockquote>
<br>
<br>
<pre class="moz-signature" cols="72">--
Joel Sherrill, Ph.D. Director of Research& Development
<a class="moz-txt-link-abbreviated" href="mailto:joel.sherrill@OARcorp.com">joel.sherrill@OARcorp.com</a> On-Line Applications Research
Ask me about RTEMS: a free RTOS Huntsville AL 35805
Support Available (256) 722-9985
</pre>
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