<div>hi joel</div>
<div> </div>
<div>Glad to receive an email from you. To me, you are the God of RTEMS world. :)</div>
<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>
<div>Best regards</div>
<div> </div>
<div>Tom</div>
<div> </div>
<div class="gmail_quote">2012/9/5 Joel Sherrill <span dir="ltr"><<a 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 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 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>> _______________________________________________<br>> rtems-users mailing list<br>> <a href="mailto:rtems-users@rtems.org" target="_blank">rtems-users@rtems.org</a><br>> <a 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 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>