x86: fix Xorg startup/shutdown slowdown with PAT

Rene Herman reported significant Xorg startup/shutdown slowdown due
to PAT. It turns out that the memtype list has thousands of entries.

Add cached_entry to list add routine, in order to speed up the
lookup for sequential reserve_memtype calls.

Reported-by: Rene Herman <rene.herman@keyaccess.nl>
Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 31 insertions, 2 deletions

diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
index 2fe30916d4b6..bb6e8a267bfe 100644
--- a/arch/x86/mm/pat.c
+++ b/arch/x86/mm/pat.c
@@ -207,6 +207,9 @@ static int chk_conflict(struct memtype *new, struct memtype *entry,
         return -EBUSY;
 }
 
+static struct memtype *cached_entry;
+static u64 cached_start;
+
 /*
  * req_type typically has one of the:
  * - _PAGE_CACHE_WB
@@ -280,11 +283,17 @@ int reserve_memtype(u64 start, u64 end, unsigned long req_type,
 
         spin_lock(&memtype_lock);
 
+        if (cached_entry && start >= cached_start)
+                entry = cached_entry;
+        else
+                entry = list_entry(&memtype_list, struct memtype, nd);
+
         /* Search for existing mapping that overlaps the current range */
         where = NULL;
-        list_for_each_entry(entry, &memtype_list, nd) {
+        list_for_each_entry_continue(entry, &memtype_list, nd) {
                 if (end <= entry->start) {
                         where = entry->nd.prev;
+                        cached_entry = list_entry(where, struct memtype, nd);
                         break;
                 } else if (start <= entry->start) { /* end > entry->start */
                         err = chk_conflict(new, entry, new_type);
@@ -292,6 +301,8 @@ int reserve_memtype(u64 start, u64 end, unsigned long req_type,
                                 dprintk("Overlap at 0x%Lx-0x%Lx\n",
                                         entry->start, entry->end);
                                 where = entry->nd.prev;
+                                cached_entry = list_entry(where,
+                                                        struct memtype, nd);
                         }
                         break;
                 } else if (start < entry->end) { /* start > entry->start */
@@ -299,7 +310,20 @@ int reserve_memtype(u64 start, u64 end, unsigned long req_type,
                         if (!err) {
                                 dprintk("Overlap at 0x%Lx-0x%Lx\n",
                                         entry->start, entry->end);
-                                where = &entry->nd;
+                                cached_entry = list_entry(entry->nd.prev,
+                                                        struct memtype, nd);
+
+                                /*
+                                 * Move to right position in the linked
+                                 * list to add this new entry
+                                 */
+                                list_for_each_entry_continue(entry,
+                                                        &memtype_list, nd) {
+                                        if (start <= entry->start) {
+                                                where = entry->nd.prev;
+                                                break;
+                                        }
+                                }
                         }
                         break;
                 }
@@ -314,6 +338,8 @@ int reserve_memtype(u64 start, u64 end, unsigned long req_type,
                 return err;
         }
 
+        cached_start = start;
+
         if (where)
                 list_add(&new->nd, where);
         else
@@ -343,6 +369,9 @@ int free_memtype(u64 start, u64 end)
         spin_lock(&memtype_lock);
         list_for_each_entry(entry, &memtype_list, nd) {
                 if (entry->start == start && entry->end == end) {
+                        if (cached_entry == entry || cached_start == start)
+                                cached_entry = NULL;
+
                         list_del(&entry->nd);
                         kfree(entry);
                         err = 0;