While profiling TSVN's SVN proper access code,
I found that about 40% of the runtime was spent in
svn_config_get_config(). The reason was the config
parser fetching individual bytes from the input stream.
However, translated_stream_read() obviously imposes
a significant overhead per call for smaller chunk sizes.
This patch quadruples the translated_stream_read()
throughput for single bytes cutting svn_config_get_config()
runtime by 50%.
-- Stefan^2.
[[[
Speed up input stream processing in config parser and
others that read single bytes from a stream.
* subversion/libsvn_subr/subst.c
(translated_stream_read): Add an optimized code path
for single byte read requests.
Patch by: Stefan Fuhrmann <stefanfuhrmann{_AT_}alice-dsl.de>
]]]
Index: subversion/libsvn_subr/subst.c
===================================================================
--- subversion/libsvn_subr/subst.c (revision 920055)
+++ subversion/libsvn_subr/subst.c (working copy)
@@ -1044,6 +1044,24 @@
apr_size_t off = 0;
apr_pool_t *iterpool;
+ /* Optimization for a frequent special case:
+ The configuration parser (and a few others) reads the
+ stream one byte at a time. All the memcpy, pool clearing
+ etc. imposes a huge overhead in that case. In most cases,
+ we can just take that single byte directly from the read
+ buffer.
+ Since *len > 1 requires lots of code to be run anyways,
+ we can afford the extra overhead of checking for *len == 1. */
+ if (unsatisfied == 1 && b->readbuf_off < b->readbuf->len)
+ {
+ /* Just take it from the read buffer */
+ *buffer = b->readbuf->data[b->readbuf_off++];
+ *len = 0;
+
+ return SVN_NO_ERROR;
+ }
+
+ /* Standard code path. */
iterpool = b->iterpool;
while (readlen == SVN__STREAM_CHUNK_SIZE && unsatisfied > 0)
{
