Improve performance of the code handling the frame queue in chan_iax2.

In my tests that exercised full frame handling in chan_iax2, the version with
these changes took 30% to 40% of the CPU time compared to the same test of
Asterisk trunk before these modifications.

While doing some profiling for <http://reviewboard.digium.com/r/205/>,
one function that caught my eye was network_thread() in chan_iax2.c.
After the things that I was working on there, it was the next target
for analysis and optimization.  I used oprofile's source annotation
functionality and found that the loop traversing the frame queue in
network_thread() was to blame for the excessive CPU cycle consumption.

The frame_queue in chan_iax2 previously held all frames that either were
pending transmission or had been transmitted and are still pending
acknowledgment.

In network_thread(), the previous code would go back through the main
for loop after reading a single incoming frame or after being signaled
because a frame had been queued up for initial transmission.  In each
iteration of the loop, it traverses the entire frame queue looking for
frames that need to be transmitted.  On a busy server, this could easily
be quite a few entries.

This patch is actually quite simple.  The frame_queue has become only a list
of frames pending acknowledgment.  Frames that need to be transmitted are
queued up to a dedicated transmit thread via the taskprocessor API.

As a result, the code in network_thread() becomes much simpler, as its only
job is to read incoming frames.

In addition to the previously described changes, this patch includes some
additional changes to the frame_queue.  Instead of one big frame_queue, now
there is a list per call number to further reduce wasted list traversals.
The biggest impact of this change is in socket_process().

For additional details on testing and test results, see the review request.

Review: http://reviewboard.digium.com/r/212/


git-svn-id: http://svn.digium.com/svn/asterisk/trunk@185432 f38db490-d61c-443f-a65b-d21fe96a405b

1 files changed, 96 insertions, 124 deletions

diff --git a/channels/chan_iax2.c b/channels/chan_iax2.c
index aa7d24e42..47f1ddc84 100644
--- a/channels/chan_iax2.c
+++ b/channels/chan_iax2.c
@@ -88,6 +88,7 @@ ASTERISK_FILE_VERSION(__FILE__, "$Revision$")
 #include "asterisk/event.h"
 #include "asterisk/astobj2.h"
 #include "asterisk/timing.h"
+#include "asterisk/taskprocessor.h"
 
 #include "iax2.h"
 #include "iax2-parser.h"
@@ -758,8 +759,12 @@ struct chan_iax2_pvt {
  * \note The contents of this list do not need to be explicitly destroyed
  * on module unload.  This is because all active calls are destroyed, and
  * all frames in this queue will get destroyed as a part of that process.
+ *
+ * \note Contents protected by the iaxsl[] locks
  */
-static AST_LIST_HEAD_STATIC(frame_queue, iax_frame);
+static AST_LIST_HEAD_NOLOCK(, iax_frame) frame_queue[IAX_MAX_CALLS];
+
+static struct ast_taskprocessor *transmit_processor;
 
 /*!
  * This module will get much higher performance when doing a lot of
@@ -1588,20 +1593,18 @@ static void pvt_destructor(void *obj)
 	struct iax_frame *cur = NULL;
 
 	ast_mutex_lock(&iaxsl[pvt->callno]);
+
 	iax2_destroy_helper(pvt);
-	ast_mutex_unlock(&iaxsl[pvt->callno]);
 
 	/* Already gone */
-	ast_set_flag(pvt, IAX_ALREADYGONE);	
+	ast_set_flag(pvt, IAX_ALREADYGONE);
 
-	AST_LIST_LOCK(&frame_queue);
-	AST_LIST_TRAVERSE(&frame_queue, cur, list) {
+	AST_LIST_TRAVERSE(&frame_queue[pvt->callno], cur, list) {
 		/* Cancel any pending transmissions */
-		if (cur->callno == pvt->callno) { 
-			cur->retries = -1;
-		}
+		cur->retries = -1;
 	}
-	AST_LIST_UNLOCK(&frame_queue);
+
+	ast_mutex_unlock(&iaxsl[pvt->callno]);
 
 	if (pvt->reg) {
 		pvt->reg->callno = 0;
@@ -2623,17 +2626,16 @@ static void __attempt_transmit(const void *data)
 		f->retries = -1;
 		freeme = 1;
 	}
-	if (callno)
-		ast_mutex_unlock(&iaxsl[callno]);
-	/* Do not try again */
+
 	if (freeme) {
 		/* Don't attempt delivery, just remove it from the queue */
-		AST_LIST_LOCK(&frame_queue);
-		AST_LIST_REMOVE(&frame_queue, f, list);
-		AST_LIST_UNLOCK(&frame_queue);
+		AST_LIST_REMOVE(&frame_queue[callno], f, list);
+		ast_mutex_unlock(&iaxsl[callno]);
 		f->retrans = -1;
 		/* Free the IAX frame */
 		iax2_frame_free(f);
+	} else if (callno) {
+		ast_mutex_unlock(&iaxsl[callno]);
 	}
 }
 
@@ -2923,7 +2925,7 @@ static char *complete_iax2_peers(const char *line, const char *word, int pos, in
 static char *handle_cli_iax2_show_stats(struct ast_cli_entry *e, int cmd, struct ast_cli_args *a)
 {
 	struct iax_frame *cur;
-	int cnt = 0, dead = 0, final = 0;
+	int cnt = 0, dead = 0, final = 0, i = 0;
 
 	switch (cmd) {
 	case CLI_INIT:
@@ -2939,15 +2941,17 @@ static char *handle_cli_iax2_show_stats(struct ast_cli_entry *e, int cmd, struct
 	if (a->argc != 3)
 		return CLI_SHOWUSAGE;
 
-	AST_LIST_LOCK(&frame_queue);
-	AST_LIST_TRAVERSE(&frame_queue, cur, list) {
-		if (cur->retries < 0)
-			dead++;
-		if (cur->final)
-			final++;
-		cnt++;
+	for (i = 0; i < ARRAY_LEN(frame_queue); i++) {
+		ast_mutex_lock(&iaxsl[i]);
+		AST_LIST_TRAVERSE(&frame_queue[i], cur, list) {
+			if (cur->retries < 0)
+				dead++;
+			if (cur->final)
+				final++;
+			cnt++;
+		}
+		ast_mutex_unlock(&iaxsl[i]);
 	}
-	AST_LIST_UNLOCK(&frame_queue);
 
 	ast_cli(a->fd, "    IAX Statistics\n");
 	ast_cli(a->fd, "---------------------\n");
@@ -3304,23 +3308,39 @@ static int schedule_delivery(struct iax_frame *fr, int updatehistory, int fromtr
 	return 0;
 }
 
-static int iax2_transmit(struct iax_frame *fr)
+static int transmit_frame(void *data)
 {
-	/* Lock the queue and place this packet at the end */
-	/* By setting this to 0, the network thread will send it for us, and
-	   queue retransmission if necessary */
-	fr->sentyet = 0;
-	AST_LIST_LOCK(&frame_queue);
-	AST_LIST_INSERT_TAIL(&frame_queue, fr, list);
-	AST_LIST_UNLOCK(&frame_queue);
-	/* Wake up the network and scheduler thread */
-	if (netthreadid != AST_PTHREADT_NULL)
-		pthread_kill(netthreadid, SIGURG);
-	ast_sched_thread_poke(sched);
+	struct iax_frame *fr = data;
+
+	ast_mutex_lock(&iaxsl[fr->callno]);
+
+	fr->sentyet = 1;
+
+	if (iaxs[fr->callno]) {
+		send_packet(fr);
+	}
+
+	if (fr->retries < 0) {
+		ast_mutex_unlock(&iaxsl[fr->callno]);
+		/* No retransmit requested */
+		iax_frame_free(fr);
+	} else {
+		/* We need reliable delivery.  Schedule a retransmission */
+		AST_LIST_INSERT_TAIL(&frame_queue[fr->callno], fr, list);
+		ast_mutex_unlock(&iaxsl[fr->callno]);
+		fr->retries++;
+		fr->retrans = iax2_sched_add(sched, fr->retrytime, attempt_transmit, fr);
+	}
+
 	return 0;
 }
 
+static int iax2_transmit(struct iax_frame *fr)
+{
+	fr->sentyet = 0;
 
+	return ast_taskprocessor_push(transmit_processor, transmit_frame, fr);
+}
 
 static int iax2_digit_begin(struct ast_channel *c, char digit)
 {
@@ -7015,16 +7035,13 @@ static int complete_transfer(int callno, struct iax_ies *ies)
 	pvt->lastsent = 0;
 	pvt->nextpred = 0;
 	pvt->pingtime = DEFAULT_RETRY_TIME;
-	AST_LIST_LOCK(&frame_queue);
-	AST_LIST_TRAVERSE(&frame_queue, cur, list) {
+	AST_LIST_TRAVERSE(&frame_queue[callno], cur, list) {
 		/* We must cancel any packets that would have been transmitted
 		   because now we're talking to someone new.  It's okay, they
 		   were transmitted to someone that didn't care anyway. */
-		if (callno == cur->callno) 
-			cur->retries = -1;
+		cur->retries = -1;
 	}
-	AST_LIST_UNLOCK(&frame_queue);
-	return 0; 
+	return 0;
 }
 
 /*! \brief Acknowledgment received for OUR registration */
@@ -7627,16 +7644,13 @@ static void vnak_retransmit(int callno, int last)
 {
 	struct iax_frame *f;
 
-	AST_LIST_LOCK(&frame_queue);
-	AST_LIST_TRAVERSE(&frame_queue, f, list) {
+	AST_LIST_TRAVERSE(&frame_queue[callno], f, list) {
 		/* Send a copy immediately */
-		if ((f->callno == callno) && iaxs[f->callno] &&
-			((unsigned char ) (f->oseqno - last) < 128) &&
-			(f->retries >= 0)) {
+		if (((unsigned char) (f->oseqno - last) < 128) &&
+				(f->retries >= 0)) {
 			send_packet(f);
 		}
 	}
-	AST_LIST_UNLOCK(&frame_queue);
 }
 
 static void __iax2_poke_peer_s(const void *data)
@@ -8653,17 +8667,15 @@ static int socket_process(struct iax2_thread *thread)
 					if (iaxdebug)
 						ast_debug(1, "Cancelling transmission of packet %d\n", x);
 					call_to_destroy = 0;
-					AST_LIST_LOCK(&frame_queue);
-					AST_LIST_TRAVERSE(&frame_queue, cur, list) {
+					AST_LIST_TRAVERSE(&frame_queue[fr->callno], cur, list) {
 						/* If it's our call, and our timestamp, mark -1 retries */
-						if ((fr->callno == cur->callno) && (x == cur->oseqno)) {
+						if (x == cur->oseqno) {
 							cur->retries = -1;
 							/* Destroy call if this is the end */
 							if (cur->final)
 								call_to_destroy = fr->callno;
 						}
 					}
-					AST_LIST_UNLOCK(&frame_queue);
 					if (call_to_destroy) {
 						if (iaxdebug)
 							ast_debug(1, "Really destroying %d, having been acked on final message\n", call_to_destroy);
@@ -8905,13 +8917,12 @@ retryowner:
 			case IAX_COMMAND_TXACC:
 				if (iaxs[fr->callno]->transferring == TRANSFER_BEGIN) {
 					/* Ack the packet with the given timestamp */
-					AST_LIST_LOCK(&frame_queue);
-					AST_LIST_TRAVERSE(&frame_queue, cur, list) {
+					AST_LIST_TRAVERSE(&frame_queue[fr->callno], cur, list) {
 						/* Cancel any outstanding txcnt's */
-						if ((fr->callno == cur->callno) && (cur->transfer))
+						if (cur->transfer) {
 							cur->retries = -1;
+						}
 					}
-					AST_LIST_UNLOCK(&frame_queue);
 					memset(&ied1, 0, sizeof(ied1));
 					iax_ie_append_short(&ied1, IAX_IE_CALLNO, iaxs[fr->callno]->callno);
 					send_command(iaxs[fr->callno], AST_FRAME_IAX, IAX_COMMAND_TXREADY, 0, ied1.buf, ied1.pos, -1);
@@ -9810,13 +9821,12 @@ immediatedial:
 				break;	
 			case IAX_COMMAND_TXMEDIA:
 				if (iaxs[fr->callno]->transferring == TRANSFER_READY) {
-					AST_LIST_LOCK(&frame_queue);
-					AST_LIST_TRAVERSE(&frame_queue, cur, list) {
+					AST_LIST_TRAVERSE(&frame_queue[fr->callno], cur, list) {
 						/* Cancel any outstanding frames and start anew */
-						if ((fr->callno == cur->callno) && (cur->transfer))
+						if (cur->transfer) {
 							cur->retries = -1;
+						}
 					}
-					AST_LIST_UNLOCK(&frame_queue);
 					/* Start sending our media to the transfer address, but otherwise leave the call as-is */
 					iaxs[fr->callno]->transferring = TRANSFER_MEDIAPASS;
 				}
@@ -10495,66 +10505,18 @@ static struct ast_channel *iax2_request(const char *type, int format, void *data
 
 static void *network_thread(void *ignore)
 {
-	/* Our job is simple: Send queued messages, retrying if necessary.  Read frames 
-	   from the network, and queue them for delivery to the channels */
-	int res, count, wakeup;
-	struct iax_frame *f;
-
-	if (timer)
+	if (timer) {
 		ast_io_add(io, ast_timer_fd(timer), timing_read, AST_IO_IN | AST_IO_PRI, NULL);
-	
-	for(;;) {
-		pthread_testcancel();
-
-		/* Go through the queue, sending messages which have not yet been
-		   sent, and scheduling retransmissions if appropriate */
-		AST_LIST_LOCK(&frame_queue);
-		count = 0;
-		wakeup = -1;
-		AST_LIST_TRAVERSE_SAFE_BEGIN(&frame_queue, f, list) {
-			if (f->sentyet)
-				continue;
-			
-			/* Try to lock the pvt, if we can't... don't fret - defer it till later */
-			if (ast_mutex_trylock(&iaxsl[f->callno])) {
-				wakeup = 1;
-				continue;
-			}
-
-			f->sentyet = 1;
-
-			if (iaxs[f->callno]) {
-				send_packet(f);
-				count++;
-			} 
-
-			ast_mutex_unlock(&iaxsl[f->callno]);
-
-			if (f->retries < 0) {
-				/* This is not supposed to be retransmitted */
-				AST_LIST_REMOVE_CURRENT(list);
-				/* Free the iax frame */
-				iax_frame_free(f);
-			} else {
-				/* We need reliable delivery.  Schedule a retransmission */
-				f->retries++;
-				f->retrans = iax2_sched_add(sched, f->retrytime, attempt_transmit, f);
-			}
-		}
-		AST_LIST_TRAVERSE_SAFE_END;
-		AST_LIST_UNLOCK(&frame_queue);
+	}
 
+	for (;;) {
 		pthread_testcancel();
-		if (count >= 20)
-			ast_debug(1, "chan_iax2: Sent %d queued outbound frames all at once\n", count);
-
-		/* Now do the IO, and run scheduled tasks */
-		res = ast_io_wait(io, wakeup);
-		if (res >= 0) {
-			if (res >= 20)
-				ast_debug(1, "chan_iax2: ast_io_wait ran %d I/Os all at once\n", res);
-		}
+		/* Wake up once a second just in case SIGURG was sent while
+		 * we weren't in poll(), to make sure we don't hang when trying
+		 * to unload. */
+		ast_io_wait(io, 1000);
 	}
+
 	return NULL;
 }
 
@@ -12426,19 +12388,14 @@ static int __unload_module(void)
 	struct ast_context *con;
 	int x;
 
-	/* Make sure threads do not hold shared resources when they are canceled */
-	
-	/* Grab the sched lock resource to keep it away from threads about to die */
-	/* Cancel the network thread, close the net socket */
 	if (netthreadid != AST_PTHREADT_NULL) {
-		AST_LIST_LOCK(&frame_queue);
 		pthread_cancel(netthreadid);
-		AST_LIST_UNLOCK(&frame_queue);
+		pthread_kill(netthreadid, SIGURG);
 		pthread_join(netthreadid, NULL);
 	}
 
 	sched = ast_sched_thread_destroy(sched);
-	
+
 	/* Call for all threads to halt */
 	AST_LIST_LOCK(&idle_list);
 	while ((thread = AST_LIST_REMOVE_HEAD(&idle_list, list)))
@@ -12489,6 +12446,7 @@ static int __unload_module(void)
 	if (timer) {
 		ast_timer_close(timer);
 	}
+	transmit_processor = ast_taskprocessor_unreference(transmit_processor);
 
 	con = ast_context_find(regcontext);
 	if (con)
@@ -12557,19 +12515,23 @@ static int load_module(void)
 	struct iax2_registry *reg = NULL;
 
 	peers = ao2_container_alloc(MAX_PEER_BUCKETS, peer_hash_cb, peer_cmp_cb);
-	if (!peers)
+	if (!peers) {
 		return AST_MODULE_LOAD_FAILURE;
+	}
+
 	users = ao2_container_alloc(MAX_USER_BUCKETS, user_hash_cb, user_cmp_cb);
 	if (!users) {
 		ao2_ref(peers, -1);
 		return AST_MODULE_LOAD_FAILURE;
 	}
+
 	iax_peercallno_pvts = ao2_container_alloc(IAX_MAX_CALLS, pvt_hash_cb, pvt_cmp_cb);
 	if (!iax_peercallno_pvts) {
 		ao2_ref(peers, -1);
 		ao2_ref(users, -1);
 		return AST_MODULE_LOAD_FAILURE;
 	}
+
 	iax_transfercallno_pvts = ao2_container_alloc(IAX_MAX_CALLS, transfercallno_pvt_hash_cb, transfercallno_pvt_cmp_cb);
 	if (!iax_transfercallno_pvts) {
 		ao2_ref(peers, -1);
@@ -12577,6 +12539,16 @@ static int load_module(void)
 		ao2_ref(iax_peercallno_pvts, -1);
 		return AST_MODULE_LOAD_FAILURE;
 	}
+
+	transmit_processor = ast_taskprocessor_get("iax2_transmit", TPS_REF_DEFAULT);
+	if (!transmit_processor) {
+		ao2_ref(peers, -1);
+		ao2_ref(users, -1);
+		ao2_ref(iax_peercallno_pvts, -1);
+		ao2_ref(iax_transfercallno_pvts, -1);
+		return AST_MODULE_LOAD_FAILURE;
+	}
+
 	ast_custom_function_register(&iaxpeer_function);
 	ast_custom_function_register(&iaxvar_function);