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<p class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US">Hi Richi,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US">You can checkout the T_busy functions here:
<a href="https://git.rtems.org/rtems/tree/cpukit/include/rtems/test.h#n2390">https://git.rtems.org/rtems/tree/cpukit/include/rtems/test.h#n2390</a><o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:10.0pt;font-family:"Courier New"">uint_fast32_t T_get_one_clock_tick_busy(void)
</span><span lang="EN-US" style="mso-fareast-language:EN-US">gives you the busy count for one tick.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:10.0pt;font-family:"Courier New""><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US">You can then calculate the number of cycles you need to wait for you desired certain time and pass it to:
</span><code><span lang="EN-US" style="font-size:10.0pt">void T_busy(uint_fast32_t)</span></code><span lang="EN-US" style="mso-fareast-language:EN-US"><o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US">This should give you comparably accurate results over different platforms.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US">Best regards,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US"> Jan<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:10.0pt;font-family:"Courier New""><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span lang="EN-US">From:</span></b><span lang="EN-US"> devel <devel-bounces@rtems.org>
<b>On Behalf Of </b>Richi Dubey<br>
<b>Sent:</b> Thursday, May 20, 2021 4:53 PM<br>
<b>To:</b> rtems-devel@rtems.org <devel@rtems.org><br>
<b>Subject:</b> Writing code that takes time to run<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US">Hi,<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US">We are thinking of writing a piece of code that takes some time to run (it would be amazing if it takes around 2 secs to run on hardware, but we would be happy with something that takes a few milliseconds as well). <o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US">We tried writing this:<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"> for(int i = 0; i<10000000; ++i){<br>
fib2 = fib0 + fib1;<br>
fib0 = fib1;<br>
fib1 = fib2;<br>
}<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US">which takes few milliseconds when tested on qemu, but only takes few microseconds on a real board. Do you have any suggestions of what else we can do?<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US">We want to write a code that is context switch safe (so, we can't simply check the time before a loop, run an infinite loop that keeps checking current time and stops after a few seconds - because this logic would fail
if there happens a context switch inside the loop and the task gets the control back after a few seconds). We also don't want to do a wake_after() since we want the task to be running on the cpu during the entire time (it is okay if the task gets preempted due
to a higher priority process), and not voluntarily giving the control to some other task.<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US">Any suggestions? The aim is to see the affect of a task getting removed from the cpu due to task shifting by the newly arrived task (in strong apa vs non task shifting scheduler).<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal">Thank you.<o:p></o:p></p>
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