Revert "Cleanup: ring buffer: remove lib_ring_buffer_switch_new_end()"

This reverts commit 5fb66f07aae4884426f1706d0281bd242a38c2a7.

The equivalent UST commit of this change broke regression tests of
lttng-tools.

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

diff --git a/lib/ringbuffer/frontend_api.h b/lib/ringbuffer/frontend_api.h
index 13975602380bf02e82979c071969be0eaa56612a..c36ec3dc2e3f0e3e8436a54ebee50b0be26d77a4 100644 (file)
--- a/lib/ringbuffer/frontend_api.h
+++ b/lib/ringbuffer/frontend_api.h
@@ -125,6 +125,14 @@ int lib_ring_buffer_try_reserve(const struct lib_ring_buffer_config *config,
         * boundary. It's safe to write.
         */
        *o_end = *o_begin + ctx->slot_size;
+
+       if (unlikely((subbuf_offset(*o_end, chan)) == 0))
+               /*
+                * The offset_end will fall at the very beginning of the next
+                * subbuffer.
+                */
+               return 1;
+
        return 0;
 }
 

diff --git a/lib/ringbuffer/ring_buffer_frontend.c b/lib/ringbuffer/ring_buffer_frontend.c
index eaeb571562230f92e4b30df3616ce3907c9b8be7..77f9e8bb4f560591f025d5b2b30b07fa4e1a777d 100644 (file)
--- a/lib/ringbuffer/ring_buffer_frontend.c
+++ b/lib/ringbuffer/ring_buffer_frontend.c
@@ -67,7 +67,8 @@
 struct switch_offsets {
        unsigned long begin, end, old;
        size_t pre_header_padding, size;
-       unsigned int switch_new_start:1, switch_old_start:1, switch_old_end:1;
+       unsigned int switch_new_start:1, switch_new_end:1, switch_old_start:1,
+                    switch_old_end:1;
 };
 
 #ifdef CONFIG_NO_HZ
@@ -1348,6 +1349,48 @@ void lib_ring_buffer_switch_new_start(struct lib_ring_buffer *buf,
                                             config->cb.subbuffer_header_size());
 }
 
+/*
+ * lib_ring_buffer_switch_new_end: finish switching current subbuffer
+ *
+ * The only remaining threads could be the ones with pending commits. They will
+ * have to do the deliver themselves.
+ */
+static
+void lib_ring_buffer_switch_new_end(struct lib_ring_buffer *buf,
+                                           struct channel *chan,
+                                           struct switch_offsets *offsets,
+                                           u64 tsc)
+{
+       const struct lib_ring_buffer_config *config = &chan->backend.config;
+       unsigned long endidx = subbuf_index(offsets->end - 1, chan);
+       unsigned long commit_count, padding_size, data_size;
+
+       data_size = subbuf_offset(offsets->end - 1, chan) + 1;
+       padding_size = chan->backend.subbuf_size - data_size;
+       subbuffer_set_data_size(config, &buf->backend, endidx, data_size);
+
+       /*
+        * Order all writes to buffer before the commit count update that will
+        * determine that the subbuffer is full.
+        */
+       if (config->ipi == RING_BUFFER_IPI_BARRIER) {
+               /*
+                * Must write slot data before incrementing commit count.  This
+                * compiler barrier is upgraded into a smp_mb() by the IPI sent
+                * by get_subbuf().
+                */
+               barrier();
+       } else
+               smp_wmb();
+       v_add(config, padding_size, &buf->commit_hot[endidx].cc);
+       commit_count = v_read(config, &buf->commit_hot[endidx].cc);
+       lib_ring_buffer_check_deliver(config, buf, chan, offsets->end - 1,
+                                 commit_count, endidx);
+       lib_ring_buffer_write_commit_counter(config, buf, chan, endidx,
+                                            offsets->end, commit_count,
+                                            padding_size);
+}
+
 /*
  * Returns :
  * 0 if ok
@@ -1541,6 +1584,7 @@ int lib_ring_buffer_try_reserve_slow(struct lib_ring_buffer *buf,
        offsets->begin = v_read(config, &buf->offset);
        offsets->old = offsets->begin;
        offsets->switch_new_start = 0;
+       offsets->switch_new_end = 0;
        offsets->switch_old_end = 0;
        offsets->pre_header_padding = 0;
 
@@ -1647,6 +1691,14 @@ int lib_ring_buffer_try_reserve_slow(struct lib_ring_buffer *buf,
                 */
        }
        offsets->end = offsets->begin + offsets->size;
+
+       if (unlikely(subbuf_offset(offsets->end, chan) == 0)) {
+               /*
+                * The offset_end will fall at the very beginning of the next
+                * subbuffer.
+                */
+               offsets->switch_new_end = 1;    /* For offsets->begin */
+       }
        return 0;
 }
 
@@ -1717,6 +1769,9 @@ int lib_ring_buffer_reserve_slow(struct lib_ring_buffer_ctx *ctx)
        if (unlikely(offsets.switch_new_start))
                lib_ring_buffer_switch_new_start(buf, chan, &offsets, ctx->tsc);
 
+       if (unlikely(offsets.switch_new_end))
+               lib_ring_buffer_switch_new_end(buf, chan, &offsets, ctx->tsc);
+
        ctx->slot_size = offsets.size;
        ctx->pre_offset = offsets.begin;
        ctx->buf_offset = offsets.begin + offsets.pre_header_padding;