From: Rajesh Venkatasubramanian <vrajesh@umich.edu>
This patch adds prefetches for walking a vm_set.list. Adding prefetches
for prio tree traversals is tricky and may lead to cache trashing. So this
patch just adds prefetches only when walking a vm_set.list.
I haven't done any benchmarks to show that this patch improves performance.
However, this patch should help to improve performance when vm_set.lists
are long, e.g., libc. Since we only prefetch vmas that are guaranteed to
be used in the near future, this patch should not result in cache trashing,
theoretically.
I didn't add any NULL checks before prefetching because prefetch.h clearly
says prefetch(0) is okay.
---
25-akpm/mm/prio_tree.c | 27 ++++++++++++++++++---------
1 files changed, 18 insertions(+), 9 deletions(-)
diff -puN mm/prio_tree.c~partial-prefetch-for-vma_prio_tree_next mm/prio_tree.c
--- 25/mm/prio_tree.c~partial-prefetch-for-vma_prio_tree_next 2004-05-04 23:06:05.652860752 -0700
+++ 25-akpm/mm/prio_tree.c 2004-05-04 23:06:05.656860144 -0700
@@ -628,28 +628,37 @@ struct vm_area_struct *vma_prio_tree_nex
* First call is with NULL vma
*/
ptr = prio_tree_first(root, iter, begin, end);
- if (ptr)
- return prio_tree_entry(ptr, struct vm_area_struct,
+ if (ptr) {
+ next = prio_tree_entry(ptr, struct vm_area_struct,
shared.prio_tree_node);
- else
+ prefetch(next->shared.vm_set.head);
+ return next;
+ } else
return NULL;
}
if (vma->shared.vm_set.parent) {
- if (vma->shared.vm_set.head)
- return vma->shared.vm_set.head;
+ if (vma->shared.vm_set.head) {
+ next = vma->shared.vm_set.head;
+ prefetch(next->shared.vm_set.list.next);
+ return next;
+ }
} else {
next = list_entry(vma->shared.vm_set.list.next,
struct vm_area_struct, shared.vm_set.list);
- if (!next->shared.vm_set.head)
+ if (!next->shared.vm_set.head) {
+ prefetch(next->shared.vm_set.list.next);
return next;
+ }
}
ptr = prio_tree_next(root, iter, begin, end);
- if (ptr)
- return prio_tree_entry(ptr, struct vm_area_struct,
+ if (ptr) {
+ next = prio_tree_entry(ptr, struct vm_area_struct,
shared.prio_tree_node);
- else
+ prefetch(next->shared.vm_set.head);
+ return next;
+ } else
return NULL;
}
EXPORT_SYMBOL(vma_prio_tree_next);
_