* [Xenomai-help] latency test
@ 2008-03-26 18:41 Hubert Talbot
2008-03-26 18:50 ` Gilles Chanteperdrix
0 siblings, 1 reply; 3+ messages in thread
From: Hubert Talbot @ 2008-03-26 18:41 UTC (permalink / raw)
To: xenomai
Hi,
800 MHz x86 system.
How can "lat max" vary to consider we have a reliable realtime system ?
If results are around 40 usec, is it normal that some values are ~75 or ~175
(especially when two other applications send/receive interrupts) ?
Does "lat max" depend on processor frequency ?
Does interrupt reception (rt_intr_wait) depend on processor frequency ?
Thanks
Hubert
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [Xenomai-help] latency test
2008-03-26 18:41 [Xenomai-help] latency test Hubert Talbot
@ 2008-03-26 18:50 ` Gilles Chanteperdrix
2008-03-26 20:01 ` Philippe Gerum
0 siblings, 1 reply; 3+ messages in thread
From: Gilles Chanteperdrix @ 2008-03-26 18:50 UTC (permalink / raw)
To: Hubert Talbot; +Cc: xenomai
On Wed, Mar 26, 2008 at 7:41 PM, Hubert Talbot <Hubert.Talbot@domain.hid> wrote:
> Hi,
>
> 800 MHz x86 system.
>
> How can "lat max" vary to consider we have a reliable realtime system ?
>
> If results are around 40 usec, is it normal that some values are ~75 or ~175
> (especially when two other applications send/receive interrupts) ?
800 MHz is rather slow, so 75 may be normal (albeit rather high), but
175 is too much. You probably have a problem with SMIs... Also normal
high peaks usually happen under load. SMI peaks happen even on an idle
system.
>
> Does "lat max" depend on processor frequency ?
I think it rather depends on processor class, as a rule of thumb, you
will probably get much lower latencies on a core 2 duo than on, say, a
pentium 2.
>
> Does interrupt reception (rt_intr_wait) depend on processor frequency ?
The latency test uses the timer interrupt, you control the sampling
period with the -p argument.
--
Gilles
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [Xenomai-help] latency test
2008-03-26 18:50 ` Gilles Chanteperdrix
@ 2008-03-26 20:01 ` Philippe Gerum
0 siblings, 0 replies; 3+ messages in thread
From: Philippe Gerum @ 2008-03-26 20:01 UTC (permalink / raw)
To: Gilles Chanteperdrix; +Cc: Hubert Talbot, xenomai
Gilles Chanteperdrix wrote:
> On Wed, Mar 26, 2008 at 7:41 PM, Hubert Talbot <Hubert.Talbot@domain.hid> wrote:
>> Hi,
>>
>> 800 MHz x86 system.
>>
>> How can "lat max" vary to consider we have a reliable realtime system ?
>>
>> If results are around 40 usec, is it normal that some values are ~75 or ~175
>> (especially when two other applications send/receive interrupts) ?
>
> 800 MHz is rather slow, so 75 may be normal (albeit rather high), but
75 us is just simply crappy on any sane x86 hw of this class. 40 us should be
achievable.
> 175 is too much. You probably have a problem with SMIs... Also normal
> high peaks usually happen under load. SMI peaks happen even on an idle
> system.
>
>> Does "lat max" depend on processor frequency ?
>
> I think it rather depends on processor class, as a rule of thumb, you
> will probably get much lower latencies on a core 2 duo than on, say, a
> pentium 2.
>
>> Does interrupt reception (rt_intr_wait) depend on processor frequency ?
>
> The latency test uses the timer interrupt, you control the sampling
> period with the -p argument.
>
--
Philippe.
^ permalink raw reply [flat|nested] 3+ messages in thread
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2008-03-26 18:41 [Xenomai-help] latency test Hubert Talbot
2008-03-26 18:50 ` Gilles Chanteperdrix
2008-03-26 20:01 ` Philippe Gerum
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