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

[PATCH] Improve single byte read stream performance

From: Stefan Fuhrman <stefanfuhrmann_at_alice-dsl.de>
Date: Sun, 07 Mar 2010 20:40:14 +0100

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)
     {
Received on 2010-03-07 20:40:54 CET

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