[Xen-devel] [PATCH] xen/common: low performance of lib/sort.c

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

From: keios <keios.cn@xxxxxxxxx>

It is a non-standard heap-sort algorithm implementation because the index
of child node is wrong .  The sort function still outputs right result, but
the performance is O( n * ( log(n) + 1 ) ) , about 10% ~ 20% worse than
standard algorithm.

Signed-off-by: keios <keios.cn@xxxxxxxxx>
[Linux commit: d3717bdf8f08a0e1039158c8bab2c24d20f492b6]

Ported to Xen.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
---
 xen/common/sort.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/xen/common/sort.c b/xen/common/sort.c
index d96fc2a..7b7544b 100644
--- a/xen/common/sort.c
+++ b/xen/common/sort.c
@@ -46,7 +46,7 @@ void sort(void *base, size_t num, size_t size,
           void (*swap)(void *, void *, int size))
 {
     /* pre-scale counters for performance */
-    int i = (num/2) * size, n = num * size, c, r;
+    int i = (num/2 - 1) * size, n = num * size, c, r;
 
     if (!swap)
         swap = (size == 4 ? u32_swap : generic_swap);
@@ -54,9 +54,9 @@ void sort(void *base, size_t num, size_t size,
     /* heapify */
     for ( ; i >= 0; i -= size )
     {
-        for ( r = i; r * 2 < n; r  = c )
+        for ( r = i; r * 2 + size < n; r  = c )
         {
-            c = r * 2;
+            c = r * 2 + size;
             if ( (c < n - size) && (cmp(base + c, base + c + size) < 0) )
                 c += size;
             if ( cmp(base + r, base + c) >= 0 )
@@ -69,9 +69,9 @@ void sort(void *base, size_t num, size_t size,
     for ( i = n - size; i >= 0; i -= size )
     {
         swap(base, base + i, size);
-        for ( r = 0; r * 2 < i; r = c )
+        for ( r = 0; r * 2 + size < i; r = c )
         {
-            c = r * 2;
+            c = r * 2 + size;
             if ( (c < i - size) && (cmp(base + c, base + c + size) < 0) )
                 c += size;
             if ( cmp(base + r, base + c) >= 0 )
-- 
2.1.4


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