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Re: Low Latency vs. Real Time Kernel - actual latencies ?



Ok, I redid all the tests, while the system was only running my DE and the test, and then again when I put it under duress by running a script that looped "du -h /" and "ls -Ral /usr/" over and over. I ran the script twice to get my proc up a bit to emulate running some intese delays and reverbs or other effects.

Ironically the kernels typically did better when the scripts were running. Personally I think there's a clear advantage with CCRMA's kernel or even just a preempt kernel in the max lat areas. Those max numbers jumped up close to where they were near the beggining of the test if anyone was wondering.

Here's the file with both sets of tests and the uname -a info as requested by Fernando.

-Brian

On Wed, Feb 22, 2012 at 6:54 AM, Brian Monroe <briancmonroe@xxxxxxxxx> wrote:

I'll be sure to include that on the next batch. I used the kernel you after installing the CCRMA repo when you use yum install kernel-rt, which happens to be  3.0.17-1.rt33.1.fc16.ccrma.x86_64.rt. I'll go back and include the other info to the old results when I do the load testing tonight or tomorrow.

On Feb 21, 2012 11:01 PM, "Fernando Lopez-Lezcano" <nando@xxxxxxxxxxxxxxxxxx> wrote:
On 02/21/2012 10:47 PM, Fernando Lopez-Lezcano wrote:
On 02/21/2012 10:28 PM, Brian Monroe wrote:
Bah, I forgot to save before I uploaded, here's the text file with the
CCRMA results.

Hi Brain,

Argh, Brian, of course... sorry...

and thanks for testing and sharing the results.
Which CCRMA rt kernel were you testing? It'd be nice if you did an uname
-a before each test...
-- Fernando

Stock 3.2.3-2 
Linux crappylappy.localdomain 3.2.3-2.fc16.x86_64 #1 SMP Fri Feb 3 20:08:08 UTC 2012 x86_64 x86_64 x86_64 GNU/Linux

no load: 
[root@crappylappy ~]# cyclictest -a -t -n -p99 -i100 -d50 -l1000000 -q
# /dev/cpu_dma_latency set to 0us
T: 0 ( 2007) P:99 I:100 C:1000000 Min:      4 Act:   16 Avg:   16 Max:    3328
T: 1 ( 2008) P:98 I:150 C: 666773 Min:      4 Act:   16 Avg:   19 Max:   16274

While under duress:
[root@crappylappy ~]# cyclictest -a -t -n -p99 -i100 -d50 -l1000000
# /dev/cpu_dma_latency set to 0us
policy: fifo: loadavg: 2.24 1.53 0.68 4/251 2413           

T: 0 ( 2367) P:99 I:100 C:1000000 Min:      4 Act:   16 Avg:   16 Max:    1894
T: 1 ( 2368) P:98 I:150 C: 666703 Min:      4 Act:   19 Avg:   16 Max:    1530



My 3.2.3-2 Preempt Kernel - 
Linux crappylappy.localdomain 3.2.3-2.lowlatency.fc16.x86_64 #1 SMP PREEMPT Wed Feb 8 22:58:16 PST 2012 x86_64 x86_64 x86_64 GNU/Linux

No Load:
[root@crappylappy ~]# cyclictest -a -t -n -p99 -i100 -d50 -l1000000 -q
# /dev/cpu_dma_latency set to 0us
T: 0 ( 1796) P:99 I:100 C:1000000 Min:      4 Act:   16 Avg:   16 Max:     612
T: 1 ( 1797) P:98 I:150 C: 666769 Min:      4 Act:   16 Avg:   16 Max:     274

While under duress:
[root@crappylappy ~]# cyclictest -a -t -n -p99 -i100 -d50 -l1000000 -q
# /dev/cpu_dma_latency set to 0us
T: 0 ( 2096) P:99 I:100 C:1000000 Min:      4 Act:    8 Avg:    7 Max:     571
T: 1 ( 2097) P:98 I:150 C: 666720 Min:      4 Act:    7 Avg:    7 Max:     576


CCRMA RT Kernel - 
Linux crappylappy.localdomain 3.0.17-1.rt33.1.fc16.ccrma.x86_64.rt #1 SMP PREEMPT RT Sat Jan 21 10:52:41 PST 2012 x86_64 x86_64 x86_64 GNU/Linux

No Load:
[root@crappylappy ~]# cyclictest -a -t -n -p99 -i100 -d50 -l1000000 -q
# /dev/cpu_dma_latency set to 0us
T: 0 ( 1872) P:99 I:100 C:1000000 Min:      6 Act:   26 Avg:   23 Max:      98
T: 1 ( 1873) P:98 I:150 C: 666682 Min:      6 Act:   20 Avg:   23 Max:      74

While under duress:
[root@crappylappy ~]# cyclictest -a -t -n -p99 -i100 -d50 -l1000000
# /dev/cpu_dma_latency set to 0us
policy: fifo: loadavg: 2.11 1.24 0.59 4/268 1998          

T: 0 ( 1981) P:99 I:100 C:1000000 Min:      5 Act:    9 Avg:   10 Max:      72
T: 1 ( 1982) P:98 I:150 C: 666691 Min:      6 Act:   13 Avg:    9 Max:      57
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