<div dir="ltr"><div>hello, dear <span style="font-family:arial,sans-serif;font-size:14.399999618530273px">Yipkei Kwok</span></div><div><br></div>is that possible that your storage constantly finish your IO request (30 IOPS ?)<div>
<br></div><div>so the pending requests does not match the request rate </div></div><div class="gmail_extra"><br><br><div class="gmail_quote">2013/7/12 <span dir="ltr"><<a href="mailto:disksim-users-request@ece.cmu.edu" target="_blank">disksim-users-request@ece.cmu.edu</a>></span><br>
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Today's Topics:<br>
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1. Problem: No. of in-flight requests bounded by 20 (Yipkei Kwok)<br>
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Message: 1<br>
Date: Wed, 10 Jul 2013 20:30:23 -0600<br>
From: Yipkei Kwok <<a href="mailto:ykwok2@miners.utep.edu">ykwok2@miners.utep.edu</a>><br>
Subject: [Disksim-users] Problem: No. of in-flight requests bounded by<br>
20<br>
To: Disksim Users Mailing List <<a href="mailto:disksim-users@ece.cmu.edu">disksim-users@ece.cmu.edu</a>><br>
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<br>
Hi,<br>
<br>
I want to use synthetic workload generators to simulate a scenario<br>
where 50 single-thread independent processes are concurrently<br>
accessing a single-disk storage system. All I/O requests are<br>
synchronous. I expect that the number of pending request in the entire<br>
I/O hierarchy (I/O driver + controller + disk) to be 50. However, I<br>
found that the number of pending requests drops from 50, at the<br>
beginning, to 20, later in the simulation.<br>
<br>
Here is the summary of the DiskSim parv file<br>
(<a href="http://utminers.utep.edu/ykwok2/tmp/20130710-0.parv.txt" target="_blank">http://utminers.utep.edu/ykwok2/tmp/20130710-0.parv.txt</a>)<br>
* I/O driver: FCFS<br>
* single disk: MAXTOR_ATLAS10K5_300 (disk model provided by Anjo at<br>
<a href="http://ovahldy.blogspot.com/2011/03/recent-diskmodels-for-disksim.html" target="_blank">http://ovahldy.blogspot.com/2011/03/recent-diskmodels-for-disksim.html</a>)<br>
* Think time from call to request = 0.0<br>
* Think time from request to return = 0.0<br>
* number of synthetic workload generators = 50<br>
* System call/return with each request = 1 (i.e., each request occurs<br>
within the context of a system call)<br>
Note: I gave a try to set "System call/return with each request" to 0<br>
but I encountered the same problem.<br>
* For each generator, Probability of time-critical request = 1.0<br>
<br>
This is how I measure the number of pending requests in the I/O<br>
hierarchy. I keep a counter in the simulator. When a request arrives<br>
the I/O driver, iodriver_request() increments the counter. When a<br>
request is serviced, iodriver_access_complete() decrements the<br>
counter.<br>
<br>
The plot of the number of pending requests vs. time is here<br>
(<a href="http://utminers.utep.edu/ykwok2/tmp/Slide1.PNG" target="_blank">http://utminers.utep.edu/ykwok2/tmp/Slide1.PNG</a>). I repeated the<br>
experiment with 35, 20, and 15 generators (all results are shown on<br>
the same slide). The number of pending requests with 35 generators,<br>
too, drops to 20, while the numbers of pending requests with 20 and 15<br>
generators remain constant.<br>
<br>
I want the number of pending requests to be 50 when 50 generators are<br>
used. Why is the number of pending requests dropping?<br>
<br>
Please kindly help. Thank you very much.<br>
<br>
Regards,<br>
Yipkei<br>
<br>
--<br>
********************************************<br>
Yipkei Kwok<br>
Ph.D. Candidate<br>
HiPerSys Lab<br>
Department of Computer Science<br>
The University of Texas at El Paso<br>
Phone: <a href="tel:915%20747%206433" value="+19157476433">915 747 6433</a> (O)<br>
E-mail: ykwok2 at miners dot utep dot edu<br>
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End of Disksim-users Digest, Vol 91, Issue 4<br>
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