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Subject[PATCH] x86: e820: 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>
---
This is a small independent part of Google's BadRAM changes mentioned in
another thread.
arch/x86/kernel/e820.c | 59 +++++++++++++++++++----------------------------
1 files changed, 24 insertions(+), 35 deletions(-)
diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c
index 3e2ef84..e2e212a 100644
--- a/arch/x86/kernel/e820.c
+++ b/arch/x86/kernel/e820.c
@@ -18,6 +18,7 @@
#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>
@@ -226,22 +227,38 @@ 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;
@@ -278,35 +295,7 @@ 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 */
--
1.7.3.1



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