Re: [Xenomai-help] ARM cached,non-cached memory

[Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>]

Sinisa Denic wrote:
> Hi, last year working with xenomai 2.4.2-3 we met problem (BUG) with memory 
> caching on ARM AT91sam9260 arch. 
> Then we were advised using non-cached memory and we've used it till now,but in 
> our next application it has big performace slow down effect and I'm 
> interested is this BUG solved in latest 2.4.10 - xenomai 
> Regards,Sinisa

Actually, there may be something we can do. In heap.c, could you try 
replacing calls to pgprot_noncached with calls to pgprot_writecombine ?

Here is a patch doing this for 2.4 head. I do not know whether it will
apply to the version you are using. But I guess you will get the idea.

diff --git a/ksrc/nucleus/heap.c b/ksrc/nucleus/heap.c
index 1c02183..d40844b 100644
--- a/ksrc/nucleus/heap.c
+++ b/ksrc/nucleus/heap.c
@@ -962,7 +962,7 @@ static inline void *__alloc_and_reserve_heap(size_t size, in
t kmflags)
                else
                        ptr = __vmalloc(size,
                                        GFP_KERNEL | __GFP_HIGHMEM,
-                                       pgprot_noncached(PAGE_KERNEL));
+                                       pgprot_writecombine(PAGE_KERNEL));
                if (ptr == NULL)
                        return NULL;

@@ -1126,7 +1126,7 @@ static int xnheap_mmap(struct file *file, struct vm_area_struct *vma)
                unsigned long maddr = vma->vm_start;

                if (heap->archdep.kmflags == XNHEAP_GFP_NONCACHED)
-                       vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
+                       vma->vm_page_prot = pgprot_writecombine(vma->vm_page_pro
t);

                while (size > 0) {
                        if (xnarch_remap_vm_page(vma, maddr, vaddr))
@@ -1147,7 +1147,7 @@ static int xnheap_mmap(struct file *file, struct vm_area_s
truct *vma)
        (void)vaddr;
        if ((heap->archdep.kmflags & ~XNHEAP_GFP_NONCACHED) != 0 ||
            heap->archdep.kmflags == XNHEAP_GFP_NONCACHED)
-               vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
+               vma->vm_page_prot = pgprot_writecombine(vma->vm_page_prot);
 #endif /* !CONFIG_MMU */

        atomic_inc(&heap->archdep.numaps);


-- 
					    Gilles.