Re: SMP driver core lock real-time driver

I beg you pardon but, since I do not see where RTAI has a place in all 
of this, I'm a bit confused.

When I want to set aside cpus dedicated to RTAI, I'll do it by setting 
the needed cpumask while insmoding rtai_hal.ko
In such a case there still remains some linux stuff, e.g, dynamically 
created workqs and timers interrupts, but it helps RTAI jitter and 
latency anyhow.

Morevor if I want to keep my dedicated cpus awake, always, I simple bind 
an idle (user space) "while(1)" task to my dedicated cpus.  Old style 
idel task getting read of all the troublesome energy savings.

I experimented also with a more aggressive policy, i.e. try to move/kill 
any task still remaining on the reserved cpus, but, even if RTAI hard 
stuff kept running, it caused troubles to Linux.

Perhaps I'm likely missing something. Is it possible I missed a previous 
email of yours?

Paolo.

On 11/21/2017 09:19 AM, Asier wrote:
>
> *Hi Doug,*
>
> **
>
> *maybe you could try to somehow tell Linux that the core is no longer 
> available/online. Could you try one of the following alternatives?*
>
> **
>
> *1- while the task is on the busy wait execute something like this: 
> (where * is the desired cpu core)*
>
> **
>
> *echo 0 > /sys/devices/system/cpu/cpu*/online*
>
> **
>
> *2- Another alternative could be to call this function *
>
> **
>
> *int cpu_down(unsigned int cpu);*
>
> **
>
> *cheers,*
>
> *Asier.*
>
>
> On Tue, Nov 21, 2017 at 3:40 AM, Doug Renton <[email protected] 
> <mailto:[email protected]>> wrote:
>
>
>      I cut and pasted a kernel module, and made it do busy work, until
>     the kernel decided it had found a bug. While the busy work was
>     going on, everything seemed fine, could not tell one core was busy.
>
>     Everything seems to run fine with one core doing my made up task,
>     until eventually the kernel decides it has found a bug.
>     With the loops at something reasonable like 999, everything runs
>     fine and my task ends. Once turned up to 999999, the kernel
>     eventually gives my module the boot. Looks like this could be
>     tricky. I still can't see why we cant just simplify everything and
>     dedicate one/two core(s) to RTAI, and busy wait.
>
>
>     [  189.566739] Timer module installing
>     [  189.566743] Starting timer to fire in 200ms (4294939693)
>     [  189.763714] my_timer_callback called (4294939743).
>     [  216.060934] NMI watchdog: BUG: soft lockup - CPU#1 stuck for
>     23s! [swapper/1:0]
>     [  216.060945] Modules linked in: hello_2(O) Bla Bla Bla...
>
>
>     /*
>      *  hello-2.c - Demonstrating the module_init() and module_exit()
>     macros.
>      *  This is preferred over using init_module() and cleanup_module().
>      */
>     #include <linux/module.h>       /* Needed by all modules */
>     #include <linux/kernel.h>       /* Needed for KERN_INFO */
>     #include <linux/init.h>         /* Needed for the macros */
>     #include <linux/timer.h>
>
>     MODULE_LICENSE("GPL");
>
>     static struct timer_list my_timer;
>
>     void my_timer_callback( unsigned long data )
>     {
>       int delay = 0;
>       int delay2;
>       int delay3;
>       int delay4;
>       volatile int glob_test;
>
>       glob_test = 1000000;
>
>
>       printk( "my_timer_callback called (%ld).\n", jiffies );
>       for ( delay4 = 0; delay4 < 99; delay4 += 1)
>       {
>       for ( delay3 = 0; delay3 < 99; delay3 += 1)
>       {
>          for ( delay2 = 0; delay2 < 99; delay2 += 1)
>          {
>             //printk( "my_timer_callback loop %d.\n",delay2);
>             for( delay = 0; delay < 99; delay += 1)
>             {
>                if (delay > glob_test) { printk("What??\n");}
>             }
>          }
>       }
>       }
>      printk( "my_timer_callback done.\n" );
>     }
>
>
>     static int __init hello_2_init(void)
>     {
>       int ret;
>       printk("Timer module installing\n");
>
>       // my_timer.function, my_timer.data
>       setup_timer( &my_timer, my_timer_callback, 0 );
>
>       printk( "Starting timer to fire in 200ms (%ld)\n", jiffies );
>       ret = mod_timer( &my_timer, jiffies + msecs_to_jiffies(200) );
>       if (ret) printk("Error in mod_timer\n");
>             return 0;
>     }
>
>     static void __exit hello_2_exit(void)
>     {
>     //      printk(KERN_INFO "Goodbye, world 2\n");
>       int ret;
>       ret = del_timer( &my_timer );
>       if (ret) printk("The timer is still in use...\n");
>
>       printk("Timer module uninstalling\n");
>
>     }
>
>     module_init(hello_2_init);
>     module_exit(hello_2_exit);
>
>
>     _______________________________________________
>     Rtai mailing list
>     [email protected] <mailto:[email protected]>
>     https://mail.rtai.org/cgi-bin/mailman/listinfo/rtai
>     <https://mail.rtai.org/cgi-bin/mailman/listinfo/rtai>
>
>
>
>
> _______________________________________________
> Rtai mailing list
> [email protected]
> https://mail.rtai.org/cgi-bin/mailman/listinfo/rtai

_______________________________________________
Rtai mailing list
[email protected]
https://mail.rtai.org/cgi-bin/mailman/listinfo/rtai