[svn.haxx.se] · SVN Dev · SVN Users · SVN Org · TSVN Dev · TSVN Users · Subclipse Dev · Subclipse Users · this month's index

[PATCH] xdelta speed improvement

From: Peter N. Lundblad <peter_at_famlundblad.se>
Date: 2006-03-21 14:59:06 CET

Hi,

While profiling, I noticed that memcpy (when called indirectly from
svn_txdelta__xdelta) was quite high in the listing. It turns out that
we can eliminate about 10% overall CPU time during a transfer of a
file with much new data by eliminating some extra buffering, which
isn't too bad given that a lot of the time is spent in libz. Here is a
patch that does this. I tested in on large .wav files and didn't get
any checksum errors, so it *should* be OK. Anyone want to have a look?

Thanks,
//Peter

[[[
Improve the speed of the xdelta algorithm by avoiding lots of small memory
copying.

* subversion/libsvn_delta/xdelta.c (find_match): Take a pointer to the
  length of the pending insert instead of a stringbuf.
  (compute_delta): Keep track of the start and length of the new data that is
  pending to insert instead of stuffing the new data (one byte at a time:-)
  in a stringbuf. Remove useless assert (for readability).
]]]

Index: subversion/libsvn_delta/xdelta.c
===================================================================
--- subversion/libsvn_delta/xdelta.c (revision 18977)
+++ subversion/libsvn_delta/xdelta.c (arbetskopia)
@@ -2,7 +2,7 @@
  * xdelta.c: xdelta generator.
  *
  * ====================================================================
- * Copyright (c) 2000-2004 CollabNet. All rights reserved.
+ * Copyright (c) 2000-2006 CollabNet. All rights reserved.
  *
  * This software is licensed as described in the file COPYING, which
  * you should have received as part of this distribution. The terms
@@ -131,17 +131,18 @@
     }
 }
 
-/* Try to find a match for the target data B in MATCHES, and then extend the
- match as long as data in A and B at the match position continues to match.
- We set the position in a we ended up in (in case we extended it backwards)
- in APOSP, the length of the match in ALENP, and the amount to advance B in
- BADVANCEP. PENDING_INSERT is a pointer to a stringbuf pointer that is the
- last insert operation that has not been committed yet to the delta stream,
- if any. This is used when extending the matches backwards, possibly
- alleviating the need for the insert entirely.
- Return TRUE if the lookup found a match, regardless of length.
- Return FALSE otherwise. */
-
+/* Try to find a match for the target data B in MATCHES, and then
+ extend the match as long as data in A and B at the match position
+ continues to match. We set the position in a we ended up in (in
+ case we extended it backwards) in APOSP, the length of the match in
+ ALENP, and the amount to advance B in BADVANCEP.
+ PENDING_INSERT_LEN is the length of the last insert operation that
+ has not been committed yet to the delta stream, or 0 if there is no
+ pending insert. This is used when extending the match backwards,
+ in which case *PENDING_INSERT_LENP is adjusted, possibly
+ alleviating the need for the insert entirely. Return TRUE if the
+ lookup found a match, regardless of length. Return FALSE
+ otherwise. */
 static svn_boolean_t
 find_match(apr_hash_t *matches,
            const struct adler32 *rolling,
@@ -153,7 +154,7 @@
            apr_size_t *aposp,
            apr_size_t *alenp,
            apr_size_t *badvancep,
- svn_stringbuf_t **pending_insert)
+ apr_size_t *pending_insert_lenp)
 {
   apr_uint32_t sum = adler32_sum(rolling);
   apr_size_t alen, badvance, apos;
@@ -186,21 +187,15 @@
     }
 
   /* See if we can extend backwards into a previous insert hunk. */
- if (*pending_insert)
+ while (apos > 0
+ && bpos > 0
+ && a[apos - 1] == b[bpos - 1]
+ && *pending_insert_lenp > 0)
     {
- while (apos > 0
- && bpos > 0
- && a[apos - 1] == b[bpos - 1]
- && (*pending_insert)->len != 0)
- {
- svn_stringbuf_chop(*pending_insert, 1);
- --apos;
- --bpos;
- ++alen;
- }
- /* If we completely consumed the entire insert, delete it. */
- if ((*pending_insert)->len == 0)
- *pending_insert = NULL;
+ --(*pending_insert_lenp);
+ --apos;
+ --bpos;
+ ++alen;
     }
 
   *aposp = apos;
@@ -248,8 +243,7 @@
 {
   apr_hash_t *matches = apr_hash_make(pool);
   struct adler32 rolling;
- apr_size_t sz, lo, hi;
- svn_stringbuf_t *pending_insert = NULL;
+ apr_size_t sz, lo, hi, pending_insert_start = 0, pending_insert_len = 0;
 
   /* Initialize the matches table. */
   init_matches_table(a, asize, MATCH_BLOCKSIZE, matches, pool);
@@ -274,33 +268,24 @@
       svn_boolean_t match;
 
       match = find_match(matches, &rolling, a, asize, b, bsize, lo, &apos,
- &alen, &badvance, &pending_insert);
+ &alen, &badvance, &pending_insert_len);
 
       /* If we didn't find a real match, insert the byte at the target
          position into the pending insert. */
       if (! match)
- {
-
- if (pending_insert != NULL)
- svn_stringbuf_appendbytes(pending_insert, b + lo, 1);
- else
- pending_insert = svn_stringbuf_ncreate(b + lo, 1, pool);
- }
+ ++pending_insert_len;
       else
         {
- /* The only legal way to end up here is to find a match. If we
- didn't find a match, we are going to generate a copy instruction
- when we should have generated an insert, so something about the
- condition above, or what the match routine did, is wrong. */
- assert(match);
-
- if (pending_insert)
+ if (pending_insert_len > 0)
             {
               svn_txdelta__insert_op(build_baton, svn_txdelta_new,
- 0, pending_insert->len,
- pending_insert->data, pool);
- pending_insert = NULL;
+ 0, pending_insert_len,
+ b + pending_insert_start, pool);
+ pending_insert_len = 0;
             }
+ /* Reset the pending insert start to immediately after the
+ match. */
+ pending_insert_start = lo + badvance;
           svn_txdelta__insert_op(build_baton, svn_txdelta_source,
                                  apos, alen, NULL, pool);
         }
@@ -316,12 +301,11 @@
     }
 
   /* If we still have an insert pending at the end, throw it in. */
- if (pending_insert)
+ if (pending_insert_len > 0)
     {
       svn_txdelta__insert_op(build_baton, svn_txdelta_new,
- 0, pending_insert->len,
- pending_insert->data, pool);
- pending_insert = NULL;
+ 0, pending_insert_len,
+ b + pending_insert_start, pool);
     }
 }
 

---------------------------------------------------------------------
To unsubscribe, e-mail: dev-unsubscribe@subversion.tigris.org
For additional commands, e-mail: dev-help@subversion.tigris.org
Received on Tue Mar 21 14:59:45 2006

This is an archived mail posted to the Subversion Dev mailing list.