[LITMUS^RT] HRT/SRT Schedulability

[Mikyung Kang]

Hello all,

I'm trying to check schedulability for simple HRT/SRT task sets using
Litmus-rt 2014.2.
* 8 Cores, no hyper-threading, 16G memory
* Bare-metal testing, Ubuntu 12.04 (Linux 3.10.41)
* rt_launch program, 20-30 seconds

On top of clean OS and litmus-rt, only rt_launch is running and then st-*
 trace files are recorded.
I expected that all cases should be schedulable and c-edf result is better
than g-edf result.
(At least, if Utilization <= 70% then c-edf schedulability >= 0.8)

But, as shown in the first following table and the second graph (bare-metal
litmus-rt),
even w/ 45% CPUs utilization (6*(120,200)=3.6), the schedulability is
dropped  so much and c-edf result isn't better than g-edf case.
The schedulability for c-edf and g-edf (6th and 7th column) is an averaged
value (20 times).

Based on other related papers, I expected that the schedulability (c-edf)
will be larger than 0.7~0.8 (at least) up to 74.4% utilization (5.95).
But, HRT and SRT, both cases produced around 0.5 schedulability.

Even though I tried 1*(180,200) ~ 8*(180,200) as shown in the third graph,
it's little bit better but still not good and fluctuation is happened.
And, even though the utillization is similar, the schedulability is very
different if the number of task sets is different.

Is this correct? How can I increase the schedulability? How can I see the
difference between c-edf and g-edf?
Is there anything that I should check for schedulability? Any tips to get
best schedulability?

(1)
   num-tasks period wcet utilization ratio bm-c-edf bm-g-edf  4.00 200.00
60.00 1.20 15.0% 0.99 1.00  4.00 200.00 100.00 2.00 25.0% 1.00 0.99  5.00
200.00 110.00 2.75 34.4% 0.87 0.92  6.00 200.00 120.00 3.60 45.0% 0.64 0.79
6.00 200.00 145.00 4.35 54.4% 0.70 0.70  7.00 200.00 150.00 5.25 65.6% 0.49
0.51  7.00 200.00 170.00 5.95 74.4% 0.50 0.59  7.00 200.00 180.00 6.30 78.8%
0.57 0.50  7.00 200.00 190.00 6.65 83.1% 0.49 0.51  8.00 200.00 180.00 7.20
90.0% 0.41 0.41
(2)


(3) 1*(180,200) ~ 8*(180,200)

​

Thanks,
Mikyung
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.litmus-rt.org/pipermail/litmus-dev/attachments/20141007/7f19bcc0/attachment.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: bm2.png
Type: image/png
Size: 80397 bytes
Desc: not available
URL: <http://lists.litmus-rt.org/pipermail/litmus-dev/attachments/20141007/7f19bcc0/attachment.png>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: bm.png
Type: image/png
Size: 59913 bytes
Desc: not available
URL: <http://lists.litmus-rt.org/pipermail/litmus-dev/attachments/20141007/7f19bcc0/attachment-0001.png>