On 07/13/2004 04:31 PM Philippe Gerum wrote:
> On Tue, 2004-07-13 at 15:33, Wolfgang Grandegger wrote:
>> On 07/13/2004 02:29 PM Philippe Gerum wrote:
>> > On Wed, 2004-07-07 at 13:37, Wolfgang Grandegger wrote:
>> >> Hi,
>> >>
>> >> I have now commited a first port of RTAI over ADEOS/ppc to the vesuvio
>> >> branch. One first observation is, that the latencies and task switch
>> >> times are almost doubled on slow PowerPC processors (MPC860 at 50 MHz).
>> >
>> >> I will give some more information on this port including performance
>> >> figures later on.
>> >>
>> >
>> > It would be interesting to know if the IRQ latencies are also observable
>> > using the irq_jitter test (or some adaptation of) from the Adeos distro
>> > (linux/examples/* IIRC).
>>
>> These figures look resonable but I cannot compare them directly with the
>> pre-ADEOS case. From my point of view, the bigger task switch times and
>> latencies are simply due to additional code to be processed, which shows
>> up on slow processors (with little caches, etc.). Are there any figures
>
> I could understand a larger overhead due to processing the pipeline with
> two stages encurring a preemption (still, it's only about 250ns on a
> Celeron 1Ghz), but I don't get yet why the task switch time is impacted.
>
>> for x86? I will provide some preliminary ones for PPC today or tomorrow.
OK, hear are some preliminary figures. I used the following PowerPC
systems for testing:
TQM855L: MPC855 at 80 MHz, 4 kB I-Cache 4 kB D-Cache
Icecube: MPC5200 at 400 MHz, 16 kB I-Cache 16 kB D-Cache
iBook2 : PowerPC 750CX at 500 MHz 256 KB L2-Cache
The following lists the results from the vesuvio's testsuite tests
"switches" and "latency". The latency test was ran under some similar
load for about 10 minutes (ping -f to the target, console output, etc.).
The results marked with "RTHAL" are for vesuvio made with a RTHAL-
patched kernel and correspondingly for "ADEOS":
TQM855L Icecube IBook2
SUSP/RES SWITCHES : 8600 3100 600 RTHAL
17300 4200 870 ADEOS
SEM SIG/WAIT SWITCHES: 11000 3300 660 RTHAL
18000 4400 950 ADEOS
Min-Latencies : 27000 7400 1400 RTHAL
47400 11000 2600 ADEOS
Max-Latencies : 86000 34000 29000 RTHAL
156000 57000 36000 ADEOS
While the latency tests under RTAI-ADEOS have an additional domain
switch involved, the task switch tests don't. Nevertheless, the soft
cli, sti, etc. functions of RTAI-ADEOS are heavier than the hard ones
used under RTHAL. I think the min-latency simply depends on the amount
of processed code as the hardware related influence is low (like cache
refills, TLB misses, etc.). Maybe there is still something not OK in my
port. I know already a few places for optimization but I don't expect
big improvements. It would be very interesting to run similar test on a
(very) slow x86 (embedded) system as well.
Apart from performance issues, stability is already quite good for RTAI
over ADEOS PowerPC.
Thanks.
Wolfgang.
