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Re: [Xen-devel] [PATCH] xen/arm: mm: optimize setup_pagetables





On 11/05/2016 10:57, Peng Fan wrote:
Hi Julien,

Hi Peng,

On Wed, May 11, 2016 at 10:31:49AM +0100, Julien Grall wrote:

[...]

diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
index 94ea054..bebd82f 100644
--- a/xen/arch/arm/mm.c
+++ b/xen/arch/arm/mm.c
@@ -443,12 +443,6 @@ void __init setup_pagetables(unsigned long 
boot_phys_offset, paddr_t xen_paddr)
      lpae_t pte, *p;
      int i;

-    /* Map the destination in the boot misc area. */
-    dest_va = BOOT_RELOC_VIRT_START;
-    pte = mfn_to_xen_entry(xen_paddr >> PAGE_SHIFT, WRITEALLOC);
-    write_pte(xen_second + second_table_offset(dest_va), pte);
-    flush_xen_data_tlb_range_va_local(dest_va, SECOND_SIZE);
-
      /* Calculate virt-to-phys offset for the new location */
      phys_offset = xen_paddr - (unsigned long) _start;

@@ -498,6 +492,11 @@ void __init setup_pagetables(unsigned long 
boot_phys_offset, paddr_t xen_paddr)
      /* Map the destination in the boot misc area. */
      dest_va = BOOT_RELOC_VIRT_START;
      pte = mfn_to_xen_entry(xen_paddr >> PAGE_SHIFT, WRITEALLOC);
+    xen_second[second_table_offset(dest_va)] = pte;
+
+    /* Map the destination in the boot misc area. */
+    dest_va = BOOT_RELOC_VIRT_START;
+    pte = mfn_to_xen_entry(xen_paddr >> PAGE_SHIFT, WRITEALLOC);

Why do you need to recompute "pte" and "dest_va"? They will be the same for
"boot_second" and "xen_second".

I just change "write_pte(xen_second + second_table_offset(dest_va), pte);" to
"xen_second[second_table_offset(dest_va)] = pte;".

The pte and dest_va are not changed.

So you could do some like:

/* Comment */
dest_va = BOOT...
pte = ...
/* Comment */
xen_second[...] = pte
/* Comment */
write_pte(boot_second...);

Regards,

--
Julien Grall

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