Fix: eliminate timestamp overlap between packets

[lttng-modules.git] / lib / ringbuffer / frontend_internal.h

diff --git a/lib/ringbuffer/frontend_internal.h b/lib/ringbuffer/frontend_internal.h
index a86abb14e683825029e138660462bcc6f02d2e66..eda800de4e1fbaeb2aac47a720ba665269689021 100644 (file)
--- a/lib/ringbuffer/frontend_internal.h
+++ b/lib/ringbuffer/frontend_internal.h
@@ -156,6 +156,9 @@ extern
 void lib_ring_buffer_switch_slow(struct lib_ring_buffer *buf,
                                 enum switch_mode mode);
 
+extern
+void lib_ring_buffer_switch_remote(struct lib_ring_buffer *buf);
+
 /* Buffer write helpers */
 
 static inline
@@ -287,17 +290,24 @@ int lib_ring_buffer_reserve_committed(const struct lib_ring_buffer_config *confi
                     - (commit_count & chan->commit_count_mask) == 0);
 }
 
+/*
+ * Receive end of subbuffer TSC as parameter. It has been read in the
+ * space reservation loop of either reserve or switch, which ensures it
+ * progresses monotonically with event records in the buffer. Therefore,
+ * it ensures that the end timestamp of a subbuffer is <= begin
+ * timestamp of the following subbuffers.
+ */
 static inline
 void lib_ring_buffer_check_deliver(const struct lib_ring_buffer_config *config,
                                   struct lib_ring_buffer *buf,
                                   struct channel *chan,
                                   unsigned long offset,
                                   unsigned long commit_count,
-                                  unsigned long idx)
+                                  unsigned long idx,
+                                  u64 tsc)
 {
        unsigned long old_commit_count = commit_count
                                         - chan->backend.subbuf_size;
-       u64 tsc;
 
        /* Check if all commits have been done */
        if (unlikely((buf_trunc(offset, chan) >> chan->backend.num_subbuf_order)
@@ -328,6 +338,12 @@ void lib_ring_buffer_check_deliver(const struct lib_ring_buffer_config *config,
                 * The subbuffer size is least 2 bytes (minimum size: 1 page).
                 * This guarantees that old_commit_count + 1 != commit_count.
                 */
+
+               /*
+                * Order prior updates to reserve count prior to the
+                * commit_cold cc_sb update.
+                */
+               smp_wmb();
                if (likely(v_cmpxchg(config, &buf->commit_cold[idx].cc_sb,
                                         old_commit_count, old_commit_count + 1)
                           == old_commit_count)) {
@@ -337,7 +353,6 @@ void lib_ring_buffer_check_deliver(const struct lib_ring_buffer_config *config,
                         * and any other writer trying to access this subbuffer
                         * in this state is required to drop records.
                         */
-                       tsc = config->cb.ring_buffer_clock_read(chan);
                        v_add(config,
                              subbuffer_get_records_count(config,
                                                          &buf->backend, idx),
@@ -370,6 +385,11 @@ void lib_ring_buffer_check_deliver(const struct lib_ring_buffer_config *config,
                        /* End of exclusive subbuffer access */
                        v_set(config, &buf->commit_cold[idx].cc_sb,
                              commit_count);
+                       /*
+                        * Order later updates to reserve count after
+                        * the commit_cold cc_sb update.
+                        */
+                       smp_wmb();
                        lib_ring_buffer_vmcore_check_deliver(config, buf,
                                                         commit_count, idx);