Re: Delays on usleep calls

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

On 2/7/2014 4:22 AM, Dario Faggioli wrote:
> From your experiments (an from some other numbers I also have) it looks 
> like this lower bound is not terrible in Xen, which is something good to
> know... So thanks again for taking the time of running the benchmarks
> and sharing the results! :-D
> 
> That being said, especially if we compare to baremetal, I think there is
> some room for improvements (I mean, there always will be an overhead,
> but still...). Do you, by any chance, have the figures for cyclictest on
> Linux baremetal too (on the same hardware and kernel, if possible)?

Dario,

Here is an updated table:

+--------+--------+-----------+-----+-------+-----+
| Config | Domain | Scheduler |   Latency (us)    |
+--------+--------+-----------+-----+-------+-----+
|        |        |           | Min |   Max | Avg |
+--------+--------+-----------+-----+-------+-----+
| 0      | NA     | CFS       |   4 |    35 |  10 |
| 1      | 0      | Arinc653  |  20 |   163 |  68 |
| 2      | 0      | Arinc653  |  21 |   173 |  68 |
| 3      | 0      | Credit    |  23 |  1041 |  87 |
| 3      | 1      | Arinc653  |  20 |   155 |  75 |
+--------+--------+-----------+-----+-------+-----+

Configuration 0 is the same kernel as before, but running on baremetal, as
requested. As expected, these values are lower than the other results. I also
added the results of running cyclictest on dom0 in configuration 3. In this
configuration, dom0 was running the credit schedule in a separate CPU-Pool from
the guest.


On another note, I attempted to get the same measurements for a linux kernel
with the Real Time Patch applied. Here are the results:

-------------------
Configuration 0 - Bare Metal Kernel

Ubuntu 12.04.1 - Linux 3.2.24-rt38

-------------------
Configuration 1 - Only Domain-0

Xen: 		4.4-rc2 - Arinc653 Scheduler
Domain-0: 	Ubuntu 12.04.1 - Linux 3.2.24-rt38

xl list -n:
Name             ID   Mem  VCPUs   State  Time(s)  NODE Affinity
Domain-0          0  1535      1  r-----     30.9  all

xl vcpu-list:
Name             ID  VCPU  CPU  State  Time(s)  CPU Affinity
Domain-0          0     0    0    r--     35.5  all

-------------------
Configuration 2 - Domain-0 and Unscheduled guest

Xen: 		4.4-rc2 - Arinc653 Scheduler
Domain-0: 	Ubuntu 12.04.1 - Linux 3.2.24-rt38
dom1: 		Ubuntu 12.04.1 - Linux 3.2.24-rt38

xl list -n:
Name             ID   Mem  VCPUs   State  Time(s)  NODE Affinity
Domain-0          0  1535      1  r-----     39.7  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--     40.5  all
dom1              1     0    0    ---      0.0  all

-------------------
Command used:

cyclictest -t1 -p 1 -i 30000 -l 500 -q

Results:
+--------+--------+-----------+-----+-------+-----+
| Config | Domain | Scheduler |   Latency (us)    |
+--------+--------+-----------+-----+-------+-----+
|        |        |           | Min |   Max | Avg |
+--------+--------+-----------+-----+-------+-----+
| 0      | NA     | CFS       |   3 |     8 |   5 |
| 1      | 0      | Arinc653  |  20 |   160 |  68 |
| 2      | 0      | Arinc653  |  18 |   150 |  66 |
+--------+--------+-----------+-----+-------+-----+

I couldn't seem to boot into the guest using the kernel with the Real Time Patch
applied, which is why I didn't replicate configuration 3.

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