[PATCH 3/5] xen/sort: Switch to an extern inline implementation

[Andrew Cooper <andrew.cooper3@citrix.com>]

There are exactly 3 callers of sort() in the hypervisor.

Both arm callers pass in NULL for the swap function.  While this might seem
like an attractive option at first, it causes generic_swap() to be used which
forced a byte-wise copy.  Provide real swap functions which the compiler can
optimise sensibly.

Furthermore, use of function pointers in tight loops like that can be very bad
for performance.  Implement sort() as extern inline, so the optimiser can
judge whether to inline things or not.

On x86, the diffstat shows how much of a better job the compiler can do when
it is able to see the cmp/swap implementations.

  $ ../scripts/bloat-o-meter xen-syms-before xen-syms-after
  add/remove: 0/5 grow/shrink: 1/1 up/down: 505/-735 (-230)
  Function                                     old     new   delta
  sort_exception_table                          31     536    +505
  u32_swap                                       9       -      -9
  generic_swap                                  34       -     -34
  cmp_ex                                        36       -     -36
  swap_ex                                       41       -     -41
  sort_exception_tables                         90      38     -52
  sort                                         563       -    -563

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
CC: Jan Beulich <JBeulich@suse.com>
CC: Roger Pau Monné <roger.pau@citrix.com>
CC: Wei Liu <wl@xen.org>
CC: Stefano Stabellini <sstabellini@kernel.org>
CC: Julien Grall <julien@xen.org>
CC: Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>
CC: Bertrand Marquis <bertrand.marquis@arm.com>
---
 xen/arch/arm/bootfdt.c |  9 +++++-
 xen/arch/arm/io.c      |  9 +++++-
 xen/include/xen/sort.h | 55 +++++++++++++++++++++++++++++++++-
 xen/lib/sort.c         | 80 ++------------------------------------------------
 4 files changed, 72 insertions(+), 81 deletions(-)

diff --git a/xen/arch/arm/bootfdt.c b/xen/arch/arm/bootfdt.c
index afaa0e249b71..e318ef960386 100644
--- a/xen/arch/arm/bootfdt.c
+++ b/xen/arch/arm/bootfdt.c
@@ -448,6 +448,13 @@ static int __init cmp_memory_node(const void *key, const void *elem)
     return 0;
 }
 
+static void __init swap_memory_node(void *_a, void *_b, size_t size)
+{
+    struct membank *a = _a, *b = _b;
+
+    SWAP(*a, *b);
+}
+
 /**
  * boot_fdt_info - initialize bootinfo from a DTB
  * @fdt: flattened device tree binary
@@ -472,7 +479,7 @@ size_t __init boot_fdt_info(const void *fdt, paddr_t paddr)
      * the banks sorted in ascending order. So sort them through.
      */
     sort(bootinfo.mem.bank, bootinfo.mem.nr_banks, sizeof(struct membank),
-         cmp_memory_node, NULL);
+         cmp_memory_node, swap_memory_node);
 
     early_print_info();
 
diff --git a/xen/arch/arm/io.c b/xen/arch/arm/io.c
index 729287e37c59..1a066f9ae502 100644
--- a/xen/arch/arm/io.c
+++ b/xen/arch/arm/io.c
@@ -80,6 +80,13 @@ static int cmp_mmio_handler(const void *key, const void *elem)
     return 0;
 }
 
+static void swap_mmio_handler(void *_a, void *_b, size_t size)
+{
+    struct mmio_handler *a = _a, *b = _b;
+
+    SWAP(*a, *b);
+}
+
 static const struct mmio_handler *find_mmio_handler(struct domain *d,
                                                     paddr_t gpa)
 {
@@ -170,7 +177,7 @@ void register_mmio_handler(struct domain *d,
 
     /* Sort mmio handlers in ascending order based on base address */
     sort(vmmio->handlers, vmmio->num_entries, sizeof(struct mmio_handler),
-         cmp_mmio_handler, NULL);
+         cmp_mmio_handler, swap_mmio_handler);
 
     write_unlock(&vmmio->lock);
 }
diff --git a/xen/include/xen/sort.h b/xen/include/xen/sort.h
index a403652948e7..01479ea44606 100644
--- a/xen/include/xen/sort.h
+++ b/xen/include/xen/sort.h
@@ -3,8 +3,61 @@
 
 #include <xen/types.h>
 
+/*
+ * sort - sort an array of elements
+ * @base: pointer to data to sort
+ * @num: number of elements
+ * @size: size of each element
+ * @cmp: pointer to comparison function
+ * @swap: pointer to swap function or NULL
+ *
+ * This function does a heapsort on the given array. You may provide a
+ * swap function optimized to your element type.
+ *
+ * Sorting time is O(n log n) both on average and worst-case. While
+ * qsort is about 20% faster on average, it suffers from exploitable
+ * O(n*n) worst-case behavior and extra memory requirements that make
+ * it less suitable for kernel use.
+ */
+#ifndef SORT_IMPLEMENTATION
+extern gnu_inline
+#endif
 void sort(void *base, size_t num, size_t size,
           int (*cmp)(const void *, const void *),
-          void (*swap)(void *, void *, size_t));
+          void (*swap)(void *, void *, size_t))
+{
+    /* pre-scale counters for performance */
+    size_t i = (num / 2) * size, n = num * size, c, r;
+
+    /* heapify */
+    while ( i > 0 )
+    {
+        for ( r = i -= size; r * 2 + size < n; r = c )
+        {
+            c = r * 2 + size;
+            if ( (c < n - size) && (cmp(base + c, base + c + size) < 0) )
+                c += size;
+            if ( cmp(base + r, base + c) >= 0 )
+                break;
+            swap(base + r, base + c, size);
+        }
+    }
+
+    /* sort */
+    for ( i = n; i > 0; )
+    {
+        i -= size;
+        swap(base, base + i, size);
+        for ( r = 0; r * 2 + size < i; r = c )
+        {
+            c = r * 2 + size;
+            if ( (c < i - size) && (cmp(base + c, base + c + size) < 0) )
+                c += size;
+            if ( cmp(base + r, base + c) >= 0 )
+                break;
+            swap(base + r, base + c, size);
+        }
+    }
+}
 
 #endif /* __XEN_SORT_H__ */
diff --git a/xen/lib/sort.c b/xen/lib/sort.c
index 35ce0d7abdec..b7e78cc0e8d2 100644
--- a/xen/lib/sort.c
+++ b/xen/lib/sort.c
@@ -4,81 +4,5 @@
  * Jan 23 2005  Matt Mackall <mpm@selenic.com>
  */
 
-#include <xen/types.h>
-
-static void u32_swap(void *a, void *b, size_t size)
-{
-    uint32_t t = *(uint32_t *)a;
-
-    *(uint32_t *)a = *(uint32_t *)b;
-    *(uint32_t *)b = t;
-}
-
-static void generic_swap(void *a, void *b, size_t size)
-{
-    char t;
-
-    do {
-        t = *(char *)a;
-        *(char *)a++ = *(char *)b;
-        *(char *)b++ = t;
-    } while ( --size > 0 );
-}
-
-/*
- * sort - sort an array of elements
- * @base: pointer to data to sort
- * @num: number of elements
- * @size: size of each element
- * @cmp: pointer to comparison function
- * @swap: pointer to swap function or NULL
- *
- * This function does a heapsort on the given array. You may provide a
- * swap function optimized to your element type.
- *
- * Sorting time is O(n log n) both on average and worst-case. While
- * qsort is about 20% faster on average, it suffers from exploitable
- * O(n*n) worst-case behavior and extra memory requirements that make
- * it less suitable for kernel use.
- */
-
-void sort(void *base, size_t num, size_t size,
-          int (*cmp)(const void *, const void *),
-          void (*swap)(void *, void *, size_t size))
-{
-    /* pre-scale counters for performance */
-    size_t i = (num / 2) * size, n = num * size, c, r;
-
-    if ( !swap )
-        swap = (size == 4 ? u32_swap : generic_swap);
-
-    /* heapify */
-    while ( i > 0 )
-    {
-        for ( r = i -= size; r * 2 + size < n; r = c )
-        {
-            c = r * 2 + size;
-            if ( (c < n - size) && (cmp(base + c, base + c + size) < 0) )
-                c += size;
-            if ( cmp(base + r, base + c) >= 0 )
-                break;
-            swap(base + r, base + c, size);
-        }
-    }
-
-    /* sort */
-    for ( i = n; i > 0; )
-    {
-        i -= size;
-        swap(base, base + i, size);
-        for ( r = 0; r * 2 + size < i; r = c )
-        {
-            c = r * 2 + size;
-            if ( (c < i - size) && (cmp(base + c, base + c + size) < 0) )
-                c += size;
-            if ( cmp(base + r, base + c) >= 0 )
-                break;
-            swap(base + r, base + c, size);
-        }
-    }
-}
+#define SORT_IMPLEMENTATION
+#include <xen/sort.h>
-- 
2.11.0