svn commit: r990572 - /subversion/branches/performance/subversion/libsvn_subr/cache-membuffer.c

[st...@apache.org]

Author: stefan2
Date: Sun Aug 29 12:00:11 2010
New Revision: 990572

URL: http://svn.apache.org/viewvc?rev=990572&view=rev
Log:
Optimize cache data transfers, especially on x86/x64. Memory copies 
are most efficient when they transfer an aligned amount of data (i.e.
multiple of 16) from aligned memory locations to aligned memory
locations. 

Locations within the cache data buffer already are aligned. This patch
aligns the copy sizes and output buffer allocated in get(). The overhead
is easily justified by the gains from copying the relatively large entries
(average is 4+kB).

* subversion/libsvn_subr/cache-membuffer.c
  (move_entry): allow for copying in 16-byte chunks
  (membuffer_cache_get): dito; align copy target as well

Modified:
    subversion/branches/performance/subversion/libsvn_subr/cache-membuffer.c

Modified: subversion/branches/performance/subversion/libsvn_subr/cache-membuffer.c
URL: http://svn.apache.org/viewvc/subversion/branches/performance/subversion/libsvn_subr/cache-membuffer.c?rev=990572&r1=990571&r2=990572&view=diff
==============================================================================
--- subversion/branches/performance/subversion/libsvn_subr/cache-membuffer.c (original)
+++ subversion/branches/performance/subversion/libsvn_subr/cache-membuffer.c Sun Aug 29 12:00:11 2010
@@ -539,6 +539,8 @@ find_entry(svn_membuffer_t *cache,
 static void
 move_entry(svn_membuffer_t *cache, entry_t *entry)
 {
+  apr_size_t size = align_entry(entry->size);
+
   /* This entry survived this cleansing run. Reset half of its
    * hit count so that its removal gets more likely in the next
    * run unless someone read / hit this entry in the meantime.
@@ -546,19 +548,22 @@ move_entry(svn_membuffer_t *cache, entry
   let_entry_age(cache, entry);
 
   /* Move the entry to the start of the empty / insertion section 
-   * (if it isn't there already) 
+   * (if it isn't there already). Size-aligned moves are legal
+   * since all offsets and block sizes share this same aligment.
+   * Size-aligned moves tend to be faster than non-aligned ones
+   * because no "odd" bytes at the end need to special treatment. 
    */
   if (entry->offset != cache->current_data)
     {
       memmove(cache->data + cache->current_data,
               cache->data + entry->offset,
-              entry->size);
+              size);
       entry->offset = cache->current_data;
     }
 
   /* The insertion position is now directly behind this entry.
    */
-  cache->current_data = align_entry(entry->offset + entry->size);
+  cache->current_data = entry->offset + size;
   cache->next = entry->next;
 }
 
@@ -876,7 +881,8 @@ membuffer_cache_get(svn_membuffer_t *cac
   apr_uint32_t group_index;
   unsigned char to_find[KEY_SIZE];
   entry_t *entry;
-  char* buffer;
+  char *buffer;
+  apr_size_t size;
 
   /* find the entry group that will hold the key.
    */
@@ -903,8 +909,10 @@ membuffer_cache_get(svn_membuffer_t *cac
       return unlock_cache(cache, SVN_NO_ERROR);
     }
 
-  buffer = apr_palloc(pool, entry->size);
-  memcpy(buffer, (const char*)cache->data + entry->offset, entry->size);
+  size = align_entry(entry->size);
+  buffer = (char *)align_entry
+               ((apr_size_t)apr_palloc(pool, size + ITEM_ALIGNMENT-1));
+  memcpy(buffer, (const char*)cache->data + entry->offset, size);
 
   /* update hit statistics
    */