[or-cvs] [tor/master] Fix gprof bottlenecks on exit nodes found by Jacob.

[Nick Mathewson]

Author: Nick Mathewson <nickm at torproject.org>
Date: Wed, 3 Jun 2009 13:52:03 -0400
Subject: Fix gprof bottlenecks on exit nodes found by Jacob.
Commit: b262e7656376a938fc149ae1bf280eeef81c6002

Apparently all the stuff that does a linear scan over all the DNS
cache entries can get really expensive when your DNS cache is very
large.  It's hard to say how much this will help performance, since
gprof doesn't count time spent in OpenSSL or zlib, but I'd guess 10%.

Also, this patch removes calls to assert_connection_ok() from inside
the read and write callbacks, which are similarly unneeded, and a
little costlier than I'm happy with.

This is probably worth backporting to 0.2.0.
---
 ChangeLog     |    8 ++++++++
 src/or/dns.c  |   18 ++++++++++++++----
 src/or/main.c |    6 +++---
 3 files changed, 25 insertions(+), 7 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 2ae76b7..b2ba413 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,4 +1,12 @@
 Changes in version 0.2.1.16-?? - 2009-??-??
+  o Major performance improvements (on 0.2.0.x):
+    - Disable and refactor some debugging checks that forced a linear scan
+      over the whole server-side DNS cache.  These accounted for over 50%
+      of CPU time on a relatively busy exit node's gprof profile. Found by
+      Jacob.
+    - Disable some debugging checks that appeared in exit node profile
+      data.
+
   o Minor bugfixes (on 0.2.0.x):
     - Log correct error messages for DNS-related network errors on
       Windows.
diff --git a/src/or/dns.c b/src/or/dns.c
index ad5b5de..74852b0 100644
--- a/src/or/dns.c
+++ b/src/or/dns.c
@@ -736,15 +736,25 @@ void
 assert_connection_edge_not_dns_pending(edge_connection_t *conn)
 {
   pending_connection_t *pend;
-  cached_resolve_t **resolve;
+  cached_resolve_t search;
 
+#if 1
+  cached_resolve_t *resolve;
+  strlcpy(search.address, conn->_base.address, sizeof(search.address));
+  resolve = HT_FIND(cache_map, &cache_root, &search);
+  if (!resolve)
+    return;
+  for (pend = resolve->pending_connections; pend; pend = pend->next) {
+    tor_assert(pend->conn != conn);
+  }
+#else
+  cached_resolve_t **resolve;
   HT_FOREACH(resolve, cache_map, &cache_root) {
-    for (pend = (*resolve)->pending_connections;
-         pend;
-         pend = pend->next) {
+    for (pend = (*resolve)->pending_connections; pend; pend = pend->next) {
       tor_assert(pend->conn != conn);
     }
   }
+#endif
 }
 
 /** Log an error and abort if any connection waiting for a DNS resolve is
diff --git a/src/or/main.c b/src/or/main.c
index a26fd0e..8fc712b 100644
--- a/src/or/main.c
+++ b/src/or/main.c
@@ -451,7 +451,7 @@ conn_read_callback(int fd, short event, void *_conn)
 
   log_debug(LD_NET,"socket %d wants to read.",conn->s);
 
-  assert_connection_ok(conn, time(NULL));
+  /* assert_connection_ok(conn, time(NULL)); */
 
   if (connection_handle_read(conn) < 0) {
     if (!conn->marked_for_close) {
@@ -483,7 +483,7 @@ conn_write_callback(int fd, short events, void *_conn)
 
   LOG_FN_CONN(conn, (LOG_DEBUG, LD_NET, "socket %d wants to write.",conn->s));
 
-  assert_connection_ok(conn, time(NULL));
+  /* assert_connection_ok(conn, time(NULL)); */
 
   if (connection_handle_write(conn, 0) < 0) {
     if (!conn->marked_for_close) {
@@ -529,7 +529,7 @@ conn_close_if_marked(int i)
     return 0; /* nothing to see here, move along */
   now = time(NULL);
   assert_connection_ok(conn, now);
-  assert_all_pending_dns_resolves_ok();
+  /* assert_all_pending_dns_resolves_ok(); */
 
   log_debug(LD_NET,"Cleaning up connection (fd %d).",conn->s);
   if ((conn->s >= 0 || conn->linked_conn) && connection_wants_to_flush(conn)) {
-- 
1.5.6.5