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>

diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
index 2fe30916d4b66aba6ea1121a9d5bfadb60f1c82f..bb6e8a267bfeb9b75fd62277add0fce45758d836 100644 (file)
--- 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;