[Xenomai] Understanding Domain Switching

[Xenomai] Understanding Domain Switching

[AG M]

Hi,

I have simple program (using POSIX skin) and I'm trying to figure out
when my program switches from primary (Xenomai) to secondary domain
(Linux)

**** Limited code. Will not compile ***
void warn_upon_switch(){

    printf("Switched to Secondary Mode \n");

}


void *threadFunc(void *arg)
{
    char *str;
    int i = 0;
    struct timespec delay, sleep;
    unsigned long over;
    int ret;

   #ifdef __XENO__
        ret = pthread_set_mode_np(0,  0x00040000);
        printf("Warn Bit Ret %d\n", ret);
   #endif /* __XENO__ */

    str=(char*)arg;
    sleep.tv_sec = 1;
    sleep.tv_nsec = 0;
    printf("Switch to secondary mode\n");

   //run this for some arbitrary time
    while(i < 100000 )
    {
        clock_nanosleep(CLOCK_REALTIME, 0, &sleep, NULL);
        //printf("threadFunc says: %s\n",str);
        ++i;
    }

    return NULL;
}

int main(void)
{
    signal(SIGXCPU, warn_upon_switch);
    pthread_t pth;
    double i = 0;
    int ret;
    pthread_attr_t tattr;
    struct sched_param sparam;
    sparam.sched_priority = 99;

    ret = pthread_attr_init(&tattr);
    //printf("Init Return Val %d\n", ret);

    ret = pthread_setschedparam(pth,SCHED_FIFO, &sparam);
    //printf("SetSchedParam Ret Value %d\n", ret);

    pthread_create(&pth,&tattr,threadFunc,"foo");

    //printf("main waiting for thread to terminate...\n");
     pthread_join(pth,NULL);

    return 0;
}

*****
 - How do I know if my program is running in primary or secondary
mode? I never get the SIGXCPU signal. Other signals like SIGINT work.
If I run the same example using the native skin, it works (using this:
http://svn.gna.org/svn/xenomai/trunk/examples/native/sigxcpu.c)

- I get the return value of ret pthread_setschedparam(pth,SCHED_FIFO,
&sparam); as 16 which is EBUSY. Any idea why? My goal is to run the
program in the highest priority if it transfers over to the secondary
domain.

- I'm also trying to figure out using /proc/xenomai/stat. This program
shows up as two processes and I see CSW and MSW have non zero values
and sometimes change. I know that it means a context switch but does
the mean its in the Linux domain?

- If the program can be seen in Linux (meaning it gets a PID through
the Linux kernel), does it mean its running in secondary mode?

I'm running Xenomai 2.6.3 and ipipe 3.
Any help is appreciated. Thanks!

- Ray

Re: [Xenomai] Understanding Domain Switching

[Philippe Gerum]

On 02/15/2017 12:49 AM, AG M wrote:
> Hi,
>

[snip]

> I have simple program (using POSIX skin) and I'm trying to figure out
> when my program switches from primary (Xenomai) to secondary domain
> (Linux)
> *****
>  - How do I know if my program is running in primary or secondary
> mode? I never get the SIGXCPU signal. Other signals like SIGINT work.

Your demo loop won't switch to secondary mode since clock_nanosleep() is
implemented by Xenomai as a real-time compatible service. Besides, using
an explicit constant instead of PTHREAD_WARNSW is a bad idea; such value
may change with the ABI across major Xenomai releases.

> If I run the same example using the native skin, it works (using this:
> http://svn.gna.org/svn/xenomai/trunk/examples/native/sigxcpu.c)
> 

Caution, this is very, very outdated code from an abandoned server (10+
years). You may want to refer to git.xenomai.org instead.

> - I get the return value of ret pthread_setschedparam(pth,SCHED_FIFO,
> &sparam); as 16 which is EBUSY. Any idea why? My goal is to run the
> program in the highest priority if it transfers over to the secondary
> domain.
>

pth is uninit memory in your example, so this code can't work. If you
have symbol wrapping enabled, Xenomai's version of
pthread_setschedparam() will be picked, affecting the scheduling policy
of the Xenomai co-kernel. If you need the regular Linux policy to be
changed, then call the glibc service via __real_pthread_setschedparam()
instead.

> - I'm also trying to figure out using /proc/xenomai/stat. This program
> shows up as two processes and I see CSW and MSW have non zero values
> and sometimes change. I know that it means a context switch but does
> the mean its in the Linux domain?
> 

MSW counts primary -> secondary transitions, i.e. from rt to Linux.

> - If the program can be seen in Linux (meaning it gets a PID through
> the Linux kernel), does it mean its running in secondary mode?
> 

No, this is unrelated. A Xenomai thread running in primary mode appears
as sleeping for the Linux kernel.

> I'm running Xenomai 2.6.3 and ipipe 3.
> Any help is appreciated. Thanks!
> 

Xenomai 2.6.x reached EOL a year ago. Xenomai 3 is maintained.

-- 
Philippe.

Re: [Xenomai] Understanding Domain Switching

[AG M]

Thanks Philippe.

I commented out all the pthread stuff and just ran a while loop
without any Linux system calls. I still see that MSW immediately
become 1 as soon as I start the program. It looks like the program is
immediately going to the secondary domain as soon as I run it (also I
wonder why I dont get the SIGXCPU signal now that I know its doing a
domain switch). My program at this point is a simple while loop.
Here's my Makefile

###### CONFIGURATION ######

### List of applications to be build
APPLICATIONS = main_posix

### Note: to override the search path for the xeno-config script, use
"make XENO=..."


### List of modules to be build
MODULES = main_posix

### Note: to override the kernel source path, use "make KSRC=..."

all::

satch: main_posix.c


###### USER SPACE BUILD (no change required normally) ######
ifeq ($(KERNELRELEASE),)
ifneq ($(APPLICATIONS),)

### Default Xenomai installation path
XENO ?= /usr/xenomai

XENOCONFIG=$(shell PATH=$(XENO):$(XENO)/bin:$(PATH) which xeno-config
2>/dev/null)

### Sanity check
ifeq ($(XENOCONFIG),)
all::
@echo ">>> Invoke make like this: \"make XENO=/path/to/xeno-config\" <<<"
@echo
endif


CC=$(shell $(XENOCONFIG) --cc)

CFLAGS=-DCONSUMER $(shell $(XENOCONFIG) --skin=posix --cflags) $(APP_CFLAGS)

LDFLAGS=$(shell $(XENOCONFIG) --skin=posix --ldflags) $(APP_LDFLAGS)

# This includes the library path of given Xenomai into the binary to make live
# easier for beginners if Xenomai's libs are not in any default search path.
LDFLAGS+=-Xlinker -rpath -Xlinker $(shell $(XENOCONFIG) --libdir)

all:: $(APPLICATIONS)

clean::
$(RM) $(APPLICATIONS) *.o

endif
endif


clean::
$(RM) $(CLEANMOD) *.o *.ko *.mod.c Module*.symvers Module.markers modules.order
$(RM) -R .tmp*
$(RM) .runinfo


My ultimate goal is to port my Linux based app to Xenomai. The
application has a lot of communication modules (WiFi, Ethernet, USB
etc. ) and some computing. I went through some of the old mailing
lists and found the following
1. Using RTDM based model does not necessarily guarantee hard
deadlines for communication/disk related activities. Keeping that in
mind, if I do all the communication and disk related activities with
Linux and do the computing/prcoessing (or something which does not
require Linux system call) with Xenomai, what would be the best way
for these to exchange information? For ex: I want to linux to fetch
data from TCP socket and Xenomai thread to process that data.
2.When it executing a non-rt service, it switches to the secondary
domain and then comes back to primary if it is rt-related. How can I
detect this secondary--> primary switch?

Thanks for your help!



On Wed, Feb 15, 2017 at 8:29 AM, Philippe Gerum <rpm@xenomai.org> wrote:
> On 02/15/2017 12:49 AM, AG M wrote:
>> Hi,
>>
>
> [snip]
>
>> I have simple program (using POSIX skin) and I'm trying to figure out
>> when my program switches from primary (Xenomai) to secondary domain
>> (Linux)
>> *****
>>  - How do I know if my program is running in primary or secondary
>> mode? I never get the SIGXCPU signal. Other signals like SIGINT work.
>
> Your demo loop won't switch to secondary mode since clock_nanosleep() is
> implemented by Xenomai as a real-time compatible service. Besides, using
> an explicit constant instead of PTHREAD_WARNSW is a bad idea; such value
> may change with the ABI across major Xenomai releases.
>
>> If I run the same example using the native skin, it works (using this:
>> http://svn.gna.org/svn/xenomai/trunk/examples/native/sigxcpu.c)
>>
>
> Caution, this is very, very outdated code from an abandoned server (10+
> years). You may want to refer to git.xenomai.org instead.
>
>> - I get the return value of ret pthread_setschedparam(pth,SCHED_FIFO,
>> &sparam); as 16 which is EBUSY. Any idea why? My goal is to run the
>> program in the highest priority if it transfers over to the secondary
>> domain.
>>
>
> pth is uninit memory in your example, so this code can't work. If you
> have symbol wrapping enabled, Xenomai's version of
> pthread_setschedparam() will be picked, affecting the scheduling policy
> of the Xenomai co-kernel. If you need the regular Linux policy to be
> changed, then call the glibc service via __real_pthread_setschedparam()
> instead.
>
>> - I'm also trying to figure out using /proc/xenomai/stat. This program
>> shows up as two processes and I see CSW and MSW have non zero values
>> and sometimes change. I know that it means a context switch but does
>> the mean its in the Linux domain?
>>
>
> MSW counts primary -> secondary transitions, i.e. from rt to Linux.
>
>> - If the program can be seen in Linux (meaning it gets a PID through
>> the Linux kernel), does it mean its running in secondary mode?
>>
>
> No, this is unrelated. A Xenomai thread running in primary mode appears
> as sleeping for the Linux kernel.
>
>> I'm running Xenomai 2.6.3 and ipipe 3.
>> Any help is appreciated. Thanks!
>>
>
> Xenomai 2.6.x reached EOL a year ago. Xenomai 3 is maintained.
>
> --
> Philippe.