Re: [Xenomai-help] Running out of stack memory in kernel-space

[Philippe Gerum <rpm@xenomai.org>]

On Thu, 2009-05-28 at 14:23 -0400, Andreas Glatz wrote:
> On Thu, 2009-05-28 at 18:39 +0200, Philippe Gerum wrote:
> > On Thu, 2009-05-28 at 11:59 -0400, Andreas Glatz wrote:
> > > Hi,
> > > 
> > > We have to start 40+ Xenomai tasks in kernel space.
> > > We want to allocate at least 4kbyte of stack memory
> > > for each of them. So we need the stack heap size 
> > > to be more than 160kbyte. 
> > > 
> > > In the documentation it says that the total 
> > > stack heap size cannot be more than 128kbyte
> > > (the limit of kmalloc).
> > 
> > Could you point me at that doc? TIA,
> > 
> > > 
> > > Now my idea is to modify the Xenomai code to have 
> > > more than one stack heaps. So when I'm running out
> > > of space in one heap I can switch to the next heap...
> > > 
> > > Is there an easier way to increase the max. stack heap size?
> > > 
> > 
> > See CONFIG_XENO_OPT_SYS_STACKPOOLSZ, nucleus configuration menu.
> 
> I found this in kernel/xenomai/nucleus/Kconfig :
> 
> config XENO_OPT_SYS_STACKPOOLSZ
>         depends on XENO_GENERIC_STACKPOOL
>     int "Size of the private stack pool (Kb)"
>     default 32
>     range 0 128
>     help
> 
>     On this architecture, kernel-based Xenomai threads get the
>     stack space they need from a private memory pool.  If you
>     don't start any kernel-based thread (i.e. no RTDM driver
>     thread, and no real-time task created from an application
>     embodied into a kernel module), you may leave a zero value for
>     this option. The size is expressed in Kilobytes.
> 

Ok, you must be running a Xenomai release prior to 2.4.7 where this
useless limitation was lifted. I would really, really, really, really,
indeed, I mean, no kidding, I swear, life will be good after this,
recommend (*) that you upgrade to 2.4.8 when it is available.

For the time being, you could just get rid of the 128k limit with that
patch:

--- ksrc/nucleus/Kconfig~	2008-11-09 18:54:04.000000000 +0100
+++ ksrc/nucleus/Kconfig	2009-05-29 00:10:05.000000000 +0200
@@ -145,7 +145,6 @@
         depends on XENO_GENERIC_STACKPOOL
 	int "Size of the private stack pool (Kb)"
 	default 32
-	range 0 128
 	help
 
 	On this architecture, kernel-based Xenomai threads get the

(*) no, seriously.

> 
> And if you follow the CONFIG_XENO_OPT_SYS_STACKPOOLSZ macro 
> you eventually end up at this comment in kernel/xenomai/nucleus/pod.c :
> 
>     /*
>      * We have to differentiate the system heap memory from the
>      * pool the kernel thread stacks will be obtained from,
>      * because on some architectures, vmalloc memory may not be
>      * accessed while running in physical addressing mode
>      * (e.g. exception trampoline code on powerpc with standard
>      * MMU support - CONFIG_PPC_STD_MMU). Meanwhile, since we want
>      * to allow the system heap to be larger than 128Kb in
>      * contiguous memory, we can't restrict to using kmalloc()
>      * memory for it either.  Therefore, we manage a private stack
>      * pool for kernel-based threads which will be populated with
>      * the kind of memory the underlying arch requires, still
>      * allowing the system heap to rely on a vmalloc'ed segment.
>      */
>     heapaddr = xnarch_alloc_stack_mem(CONFIG_XENO_OPT_SYS_STACKPOOLSZ *
> 1024);

I will fix this leftover in 2.4.8, thanks.

> 
> 
> 
> Andreas
> 
-- 
Philippe.