Changeset 47c4490 for lib

Timestamp:

12/15/16 17:06:24 (4 years ago)

Author:

Richard Sanger <rsanger@…>

Branches:

4.0.1-hotfixes, cachetimestamps, develop, dpdk-ndag, etsilive, master, ndag_format, rc-4.0.1, rc-4.0.2, rc-4.0.3, rc-4.0.4, ringdecrementfix, ringperformance, ringtimestampfixes

Children:

4edb310, ceba2b2, e47ab4d

Parents:

f8613e4

Message:

Second round of fixes for Issue #39

1. Fixes a bug in the ring format where packets could be mistakenly read twice if the packet is not 'finished' before the ring loops. This was only a problem in the parallel API and for old kernels without FANOUT support, where packets are not always finished straight away.

2. Only read a batch of 1 packet from live formats when falling back to FIFO locking. This reduces latency, and in the case of ring stops us from ending up in a loop polling 100% CPU. This occurs as the kernel tracks the most recent packet it has put in the ring, but this is still set to TP_STATUS_USER as it is still waiting in the batch.

3. Move the trace_interrupt code to include the 100% poll loop case above. In normal cases we won't end up here but could if an application holds on to a packet.

Location:

lib

Files:

• format_linux_ring.c (modified) (5 diffs)
• trace_parallel.c (modified) (1 diff)

lib/format_linux_ring.c

@@ -447 +447 @@
 #ifdef HAVE_NETPACKET_PACKET_H
 #define LIBTRACE_MIN(a,b) ((a)<(b) ? (a) : (b))
+/* We use TP_STATUS_LIBTRACE to ensure we don't loop back on ourself
+ * and read the same packet twice if an old packet has not yet been freed */
+#define TP_STATUS_LIBTRACE 0xFFFFFFFF
+
 inline static int linuxring_read_stream(libtrace_t *libtrace,
                                         libtrace_packet_t *packet,
@@ -470 +474 @@
          * ready for consumption.
          */
-        while (!(header->tp_status & TP_STATUS_USER)) {
+        while (!(header->tp_status & TP_STATUS_USER) ||
+               header->tp_status == TP_STATUS_LIBTRACE) {
+                if ((ret=is_halted(libtrace)) != -1)
+                        return ret;
                 pollset[0].fd = stream->fd;
                 pollset[0].events = POLLIN;
@@ -509 +516 @@
                         }
                 } else {
-                        /* Poll timed out - check if we should exit */
-                        if ((ret=is_halted(libtrace)) != -1)
-                                return ret;
+                        /* Poll timed out - check if we should exit on next loop */
                         continue;
                 }
@@ -518 +523 @@
         packet->buffer = header;
         packet->trace = libtrace;
+        header->tp_status = TP_STATUS_LIBTRACE;
 
         /* If a snaplen was configured, automatically truncate the packet to
@@ -574 +580 @@
         /* Fetch the current frame */
         header = GET_CURRENT_BUFFER(FORMAT_DATA_FIRST);
-        if (header->tp_status & TP_STATUS_USER) {
+        if (header->tp_status & TP_STATUS_USER &&
+            header->tp_status != TP_STATUS_LIBTRACE) {
                 /* We have a frame waiting */
                 event.size = trace_read_packet(libtrace, packet);

lib/trace_parallel.c

@@ -1733 +1733 @@
                 if (libtrace->perpkt_thread_count > 1)
                         libtrace->pread = trace_pread_packet_first_in_first_served;
+                        /* Don't wait for a burst of packets if the format is
+                         * live as this could block ring based formats and
+                         * introduces delay. */
+                        if (libtrace->format->info.live) {
+                                libtrace->config.burst_size = 1;
+                        }
                 else
                         /* Use standard read_packet */