Hi,
I am in the process of evaluation 2.6 series kernel soft real-time
performance on the Coldfire. Currently I am using the 2.6.17 kernel and
GCC 4.1.1 on the M5329 board at 240Mhz, here is my brief measurement of
IRQ latency:
1) no load
Average: 8uS
Worst: 17.4uS
2) running "cat /dev/zero > /dev/null" process at the background
Average: 8uS
Worst: 24.8uS
3) running a ping flood to the dev board from host box:
Average: 13.4uS
Worst: 26.8uS
The test is not very rigid, and each test only take 600 samples over
60seconds. It seems to me these IRQ latency timing is comparable to
others' measurements.
However my concern is more related to the context switch timing (the
user process get scheduled after IRQ happens), the worst case
measurement under the ping flood is the 24mS. Is there any way to
schedule a user process more quickly after IRQ happened under the heavy
system load? I know I can push the user process into the kernel space to
get the fast response time, but........
Also can anyone tell me which features 2.6.22 uClinux kernel have
improved in the regards of soft real-time abilities? I understand the
CFS maybe has a big impacts on the desktop tasks performance, but I am
not too sure if it has impacts on embedded system running uClinux.
Cheers
Xin Xie
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of Michael Schnell
Sent: Thursday, November 22, 2007 11:31 PM
To: uClinux development list
Subject: Re: [uClinux-dev] Interrupt latency on M5272
Linux is not a hard realtime OS !
So no maximum latency can be specified. Even not for ISRs (there is no
spec how low at max the interrupt might be disabled). For Linux there is
just some _soft_ realtime spec, meaning that the probability for a delay
in lower than a certain value.
Kernel 2.4 is outdated and know for much worse soft realtime abilities.
2.6 is better and with 2.6.22 some more improvements have been
implemented
If you need hard realtime you need to add things like RTAI or PikeOS.
-Michael
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