From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Mon, 23 Jan 2012 17:06:06 +0000 (-0500)
Subject: Force 64-bit timestamps
X-Git-Tag: v1.9.5~15
X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=aae88c703374f4b1fbb8a5e7e95591bf8ce3e837;p=lttng-ust.git

Force 64-bit timestamps

commit 9080554ff25b08f48762d2ee7cfa3981317e9c1d attempted to fix the
timestamp problem by using large event headers. It incorrectly stated
that those headers "use a 64-bit timestamp field". In fact, they use a
32-bit timestamp field (not 64). So they were helping (it was better
than using a 27-bit field), but the problem could still appear. It's
only when the RING_BUFFER_RFLAG_FULL_TSC is set that the ring buffer
forces use of the 64-bit fields.

Fix this for good by setting this flag.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
---

diff --git a/liblttng-ust/ltt-events.c b/liblttng-ust/ltt-events.c
index ee88b431..9751089c 100644
--- a/liblttng-ust/ltt-events.c
+++ b/liblttng-ust/ltt-events.c
@@ -309,20 +309,10 @@ int ltt_session_enable(struct ltt_session *session)
 	cds_list_for_each_entry(chan, &session->chan, list) {
 		if (chan->header_type)
 			continue;		/* don't change it if session stop/restart */
-		/*
-		 * Because we don't use any timer in the application, we
-		 * currently cannot guarantee that we have frequent
-		 * events that let us detect 27-bit overflows.
-		 * Therefore, for now, we force large event headers,
-		 * which contain 64-bit timestamps.
-		 */
-		chan->header_type = 2;  /* large */
-#if 0
 		if (chan->free_event_id < 31)
 			chan->header_type = 1;	/* compact */
 		else
 			chan->header_type = 2;	/* large */
-#endif //0
 	}
 
 	CMM_ACCESS_ONCE(session->active) = 1;
diff --git a/liblttng-ust/ltt-ring-buffer-client.h b/liblttng-ust/ltt-ring-buffer-client.h
index a2ace400..b180b793 100644
--- a/liblttng-ust/ltt-ring-buffer-client.h
+++ b/liblttng-ust/ltt-ring-buffer-client.h
@@ -365,7 +365,7 @@ static const struct lttng_ust_lib_ring_buffer_config client_config = {
 	.cb.buffer_create = client_buffer_create,
 	.cb.buffer_finalize = client_buffer_finalize,
 
-	.tsc_bits = 32,
+	.tsc_bits = 27,
 	.alloc = RING_BUFFER_ALLOC_PER_CPU,
 	.sync = RING_BUFFER_SYNC_GLOBAL,
 	.mode = RING_BUFFER_MODE_TEMPLATE,
diff --git a/libringbuffer/frontend_api.h b/libringbuffer/frontend_api.h
index 49f6e4c2..d5a2f2a0 100644
--- a/libringbuffer/frontend_api.h
+++ b/libringbuffer/frontend_api.h
@@ -93,8 +93,18 @@ int lib_ring_buffer_try_reserve(const struct lttng_ust_lib_ring_buffer_config *c
 	 */
 	//prefetch(&buf->commit_hot[subbuf_index(*o_begin, chan)]);
 
+	/*
+	 * Because we don't use any timer in the application, we
+	 * currently cannot guarantee that we have frequent
+	 * events that let us detect 27-bit overflows.
+	 * Therefore, for now, we force event headers
+	 * to contain 64-bit timestamps.
+	 */
+	ctx->rflags |= RING_BUFFER_RFLAG_FULL_TSC;
+#if 0
 	if (last_tsc_overflow(config, buf, ctx->tsc))
 		ctx->rflags |= RING_BUFFER_RFLAG_FULL_TSC;
+#endif //0
 
 	if (caa_unlikely(subbuf_offset(*o_begin, chan) == 0))
 		return 1;