Re: Delays on usleep calls

[Robbie VanVossen <robert.vanvossen@dornerworks.com>]

On 1/20/2014 10:05 AM, Dario Faggioli wrote:
>> Test program makes nothing but sleeping for 30 (5, 500) ms then
>> printing timestamp in an endless loop. 
>>
> Ok, so something similar to cyclictest, right?
> 
> https://rt.wiki.kernel.org/index.php/Cyclictest
> 
> I'm also investigating on running it in a bunch of consideration... I'll
> have results that we can hopefully compare to yours very soon.
> 
> What about giving a try to it yourself? I think standardizing on one (a
> set of) specific tool could be a good thing.

Dario,

We thought we would try to get some similar readings for the Arinc653 scheduler.
We followed your suggestions from this thread and have gotten some readings for
the following configurations:

----------------
Configuration 1 - Only Domain-0
Xen: 		4.4-rc2 - Arinc653 Scheduler
Domain-0: 	Ubuntu 12.04.1 - Linux 3.2.0-35

xl list -n:
Name                       ID   Mem VCPUs     State	Time(s)  NODE Affinity
Domain-0                    0  1535     1     r-----      100.2  all

xl vcpu-list:
Name                                ID  VCPU   CPU State   Time(s) CPU Affinity
Domain-0                             0     0    0   r--     103.0  all

----------------
Configuration 2 - Domain-0 and Unscheduled guest
Xen: 		4.4-rc2 - Arinc653 Scheduler
Domain-0: 	Ubuntu 12.04.1 - Linux 3.2.0-35
dom1: 		Ubuntu 12.04.1 - Linux 3.2.0-35

xl list -n:
Name                  ID   Mem VCPUs	State	Time(s) NODE Affinity
Domain-0               0  1535     1    r-----     146.4 all
dom1                   1   512     1    ------       0.0 all

xl vcpu-list:
Name                  ID  VCPU   CPU State   Time(s) CPU Affinity
Domain-0               0     0    0   r--     147.4  all
dom1                   1     0    0   ---       0.0  all

----------------
Configuration 3 - Domain-0 and Scheduled guest (In separate CPU Pools)
Xen: 		4.4-rc2 - Credit Scheduler
Pool: Pool-0 - Credit Scheduler
Domain-0: 	Ubuntu 12.04.1 - Linux 3.2.0-35
Pool: arinc  - Arinc653 Scheduler
dom1: 		Ubuntu 12.04.1 - Linux 3.2.0-35

xl list -n:
Name                            ID   Mem VCPUs	State	Time(s) NODE Affinity
Domain-0                         0  1535     2  r-----   111.5  all
dom1                             1   512     1   b----     4.3  all

xl vcpu-list:
Name                                ID  VCPU   CPU State   Time(s) CPU Affinity
Domain-0                             0     0    0   -b-      81.0  all
Domain-0                             0     1    0   r--      47.1  all
dom1                                 1     0    1   -b-       4.7  all

----------------

We used the following command to get results for a 30 millisecond (30,000us)
interval with 500 loops:

cyclictest -t1 -i 30000 -l 500 -q

Results:

+--------+--------+-----------+-------+-------+-------+
| Config | Domain | Scheduler |      Latency (us)     |
|        |        |           |   Min |   Max |   Avg |
+--------+--------+-----------+-------+-------+-------+
|      1 |      0 |  Arinc653 |    20 |   163 |    68 |
|      2 |      0 |  Arinc653 |    21 |   173 |    68 |
|      3 |      1 |  Arinc653 |    20 |   155 |    75 |
+--------+--------+-----------+-------+-------+-------+

It looks like we get negligible latencies for each of these simplistic
configurations.

Thanks,

-- 
---
Robbie VanVossen
DornerWorks, Ltd.
Embedded Systems Engineering