[Xenomai-core] Timing Issues on x86_32 SMP

[Xenomai-core] Timing Issues on x86_32 SMP

[Benjamin ZORES]

Hi,

I'm currently running an x86_32 SMP system and facing some issues with 
periodic tasks.
I'd like to get a bit more information on a few assumptions I've made.

Quick sum-up of my setup:
- adeos-ipipe-2.6.23-i386-1.12-03
- xenomai-2.4.3.patch
- Core 2 Duo x86_32 running in SMP
- Linux 2.6.23.17
- Timer frequency: 1000 Hz
- Tick-less mode activated (CONFIG_NO_HZ)
- Xenomai Periodic Timing enabled (CONFIG_XENO_OPT_TIMING_PERIODIC)
- tasks are kernel-based.

I'm trying to schedule a periodic task each 8ms and I'm running into 
period miss
(loosing from 5 up to 75, which is quite A LOT). The problem however 
doesn't appear
on UP system (or at least when booting the kernel with maxcpus=1 ).

I'd like to have more information regarding timer handling.

First, I create my 8ms periodic task, the following way:

    SRTIME ticks;
    int period = 8;

    /* need to feed with nano-seconds, then convert to CPU ticks */
    ticks = rt_timer_ns2ticks(1000000 * period);
    rt_task_set_periodic (task, TM_NOW, ticks);

Is it the correct way to do ?
It seems the rt_timer_ns2ticks() function is useless, i.e. it seems that 
1 tick = 1 ns,
which sees weird to me.

Also, what does the rt_timer_read() function really return in my context ?
Jiffies ? Nanoseconds ? Clock ticks ?
 From the different headers and documentation pieces I've read, none 
seem to be really
explicit regarding the returned value.

Any help, is really appreciated.

Ben

Re: [Xenomai-core] Timing Issues on x86_32 SMP

[Gilles Chanteperdrix]

On Tue, May 6, 2008 at 10:11 AM, Benjamin ZORES
<benjamin.zores@domain.hid> wrote:
> Hi,
>
>  I'm currently running an x86_32 SMP system and facing some issues with
>  periodic tasks.
>  I'd like to get a bit more information on a few assumptions I've made.
>
>  Quick sum-up of my setup:
>  - adeos-ipipe-2.6.23-i386-1.12-03
>  - xenomai-2.4.3.patch
>  - Core 2 Duo x86_32 running in SMP

Why not x86_64 ?

>  - Linux 2.6.23.17
>  - Timer frequency: 1000 Hz
>  - Tick-less mode activated (CONFIG_NO_HZ)
>  - Xenomai Periodic Timing enabled (CONFIG_XENO_OPT_TIMING_PERIODIC)
>  - tasks are kernel-based.
>
>  I'm trying to schedule a periodic task each 8ms and I'm running into
>  period miss
>  (loosing from 5 up to 75, which is quite A LOT). The problem however
>  doesn't appear
>  on UP system (or at least when booting the kernel with maxcpus=1 ).

Have you run the latency test to know if you have no hardware issue ?

-- 
 Gilles

Re: [Xenomai-core] Timing Issues on x86_32 SMP

[Benjamin ZORES]

Gilles Chanteperdrix a écrit :
> On Tue, May 6, 2008 at 10:11 AM, Benjamin ZORES
> <benjamin.zores@domain.hid> wrote:
>   
>
> Why not x86_64 ?
>
>   
Cause I don't need 64 bits.
>
> Have you run the latency test to know if you have no hardware issue ?
>
>   
Do you have a quick way to start this test ?

Regards,

Ben

Re: [Xenomai-core] Timing Issues on x86_32 SMP

[Gilles Chanteperdrix]

On Tue, May 6, 2008 at 11:27 AM, Benjamin ZORES
<benjamin.zores@domain.hid> wrote:
> Gilles Chanteperdrix a écrit :
>
> > On Tue, May 6, 2008 at 10:11 AM, Benjamin ZORES
>  > <benjamin.zores@domain.hid> wrote:
>  >
>  >
>  > Why not x86_64 ?
>  >
>  >
>  Cause I don't need 64 bits.
>
> >
>  > Have you run the latency test to know if you have no hardware issue ?
>  >
>  >
>  Do you have a quick way to start this test ?

cd /usr/xenomai/testsuite/latency
./runt

-- 
 Gilles