arch/x86/kernel/e820.c: eliminate bubble sort from sanitize_e820_map

Replace the bubble sort in sanitize_e820_map() with a call to the generic
kernel sort function to avoid pathological performance with large maps.

On large (thousands of entries) E820 maps, the previous code took minutes
to run; with this change it's now milliseconds.

Signed-off-by: Mike Ditto <mditto@google.com>
Cc: Stefan Assmann <sassmann@kpanic.de>
Cc: Nancy Yuen <yuenn@google.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c
index 303a0e48f076feb3feb522d4052ac4b958995d42..f655f802260d69bbf3d80ffaeb9b30e32fe51124 100644 (file)
--- a/arch/x86/kernel/e820.c
+++ b/arch/x86/kernel/e820.c
@@ -19,6 +19,7 @@
 #include <linux/acpi.h>
 #include <linux/firmware-map.h>
 #include <linux/memblock.h>
+#include <linux/sort.h>
 
 #include <asm/e820.h>
 #include <asm/proto.h>
@@ -227,22 +228,38 @@ void __init e820_print_map(char *who)
  *        ____________________33__
  *        ______________________4_
  */
+struct change_member {
+       struct e820entry *pbios; /* pointer to original bios entry */
+       unsigned long long addr; /* address for this change point */
+};
+
+static int __init cpcompare(const void *a, const void *b)
+{
+       struct change_member * const *app = a, * const *bpp = b;
+       const struct change_member *ap = *app, *bp = *bpp;
+
+       /*
+        * Inputs are pointers to two elements of change_point[].  If their
+        * addresses are unequal, their difference dominates.  If the addresses
+        * are equal, then consider one that represents the end of its region
+        * to be greater than one that does not.
+        */
+       if (ap->addr != bp->addr)
+               return ap->addr > bp->addr ? 1 : -1;
+
+       return (ap->addr != ap->pbios->addr) - (bp->addr != bp->pbios->addr);
+}
 
 int __init sanitize_e820_map(struct e820entry *biosmap, int max_nr_map,
                             u32 *pnr_map)
 {
-       struct change_member {
-               struct e820entry *pbios; /* pointer to original bios entry */
-               unsigned long long addr; /* address for this change point */
-       };
        static struct change_member change_point_list[2*E820_X_MAX] __initdata;
        static struct change_member *change_point[2*E820_X_MAX] __initdata;
        static struct e820entry *overlap_list[E820_X_MAX] __initdata;
        static struct e820entry new_bios[E820_X_MAX] __initdata;
-       struct change_member *change_tmp;
        unsigned long current_type, last_type;
        unsigned long long last_addr;
-       int chgidx, still_changing;
+       int chgidx;
        int overlap_entries;
        int new_bios_entry;
        int old_nr, new_nr, chg_nr;
@@ -279,35 +296,7 @@ int __init sanitize_e820_map(struct e820entry *biosmap, int max_nr_map,
        chg_nr = chgidx;
 
        /* sort change-point list by memory addresses (low -> high) */
-       still_changing = 1;
-       while (still_changing)  {
-               still_changing = 0;
-               for (i = 1; i < chg_nr; i++)  {
-                       unsigned long long curaddr, lastaddr;
-                       unsigned long long curpbaddr, lastpbaddr;
-
-                       curaddr = change_point[i]->addr;
-                       lastaddr = change_point[i - 1]->addr;
-                       curpbaddr = change_point[i]->pbios->addr;
-                       lastpbaddr = change_point[i - 1]->pbios->addr;
-
-                       /*
-                        * swap entries, when:
-                        *
-                        * curaddr > lastaddr or
-                        * curaddr == lastaddr and curaddr == curpbaddr and
-                        * lastaddr != lastpbaddr
-                        */
-                       if (curaddr < lastaddr ||
-                           (curaddr == lastaddr && curaddr == curpbaddr &&
-                            lastaddr != lastpbaddr)) {
-                               change_tmp = change_point[i];
-                               change_point[i] = change_point[i-1];
-                               change_point[i-1] = change_tmp;
-                               still_changing = 1;
-                       }
-               }
-       }
+       sort(change_point, chg_nr, sizeof *change_point, cpcompare, 0);
 
        /* create a new bios memory map, removing overlaps */
        overlap_entries = 0;     /* number of entries in the overlap table */