Cleanup: lib_ring_buffer_switch_new_end() only calls subbuffer_set_data_size()

[lttng-modules.git] / lib / ringbuffer / ring_buffer_frontend.c

diff --git a/lib/ringbuffer/ring_buffer_frontend.c b/lib/ringbuffer/ring_buffer_frontend.c
index 1dafe8a4162a6a24a796df28274e0f1fa7120500..077be3c8c82c530e7a8c3aef1c6da5f7857b6b00 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 +1349,28 @@ 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
+ *
+ * Calls subbuffer_set_data_size() to set the data size of the current
+ * sub-buffer. We do not need to perform check_deliver nor commit here,
+ * since this task will be done by the "commit" of the event for which
+ * we are currently doing the space reservation.
+ */
+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, data_size;
+
+       endidx = subbuf_index(offsets->end - 1, chan);
+       data_size = subbuf_offset(offsets->end - 1, chan) + 1;
+       subbuffer_set_data_size(config, &buf->backend, endidx, data_size);
+}
+
 /*
  * Returns :
  * 0 if ok
@@ -1480,6 +1503,48 @@ void lib_ring_buffer_switch_slow(struct lib_ring_buffer *buf, enum switch_mode m
 }
 EXPORT_SYMBOL_GPL(lib_ring_buffer_switch_slow);
 
+static void remote_switch(void *info)
+{
+       struct lib_ring_buffer *buf = info;
+
+       lib_ring_buffer_switch_slow(buf, SWITCH_ACTIVE);
+}
+
+void lib_ring_buffer_switch_remote(struct lib_ring_buffer *buf)
+{
+       struct channel *chan = buf->backend.chan;
+       const struct lib_ring_buffer_config *config = &chan->backend.config;
+       int ret;
+
+       /*
+        * With global synchronization we don't need to use the IPI scheme.
+        */
+       if (config->sync == RING_BUFFER_SYNC_GLOBAL) {
+               lib_ring_buffer_switch_slow(buf, SWITCH_ACTIVE);
+               return;
+       }
+
+       /*
+        * Taking lock on CPU hotplug to ensure two things: first, that the
+        * target cpu is not taken concurrently offline while we are within
+        * smp_call_function_single() (I don't trust that get_cpu() on the
+        * _local_ CPU actually inhibit CPU hotplug for the _remote_ CPU (to be
+        * confirmed)). Secondly, if it happens that the CPU is not online, our
+        * own call to lib_ring_buffer_switch_slow() needs to be protected from
+        * CPU hotplug handlers, which can also perform a remote subbuffer
+        * switch.
+        */
+       get_online_cpus();
+       ret = smp_call_function_single(buf->backend.cpu,
+                                remote_switch, buf, 1);
+       if (ret) {
+               /* Remote CPU is offline, do it ourself. */
+               lib_ring_buffer_switch_slow(buf, SWITCH_ACTIVE);
+       }
+       put_online_cpus();
+}
+EXPORT_SYMBOL_GPL(lib_ring_buffer_switch_remote);
+
 /*
  * Returns :
  * 0 if ok
@@ -1499,6 +1564,7 @@ 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;
 
@@ -1605,6 +1671,14 @@ 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;
 }
 
@@ -1675,6 +1749,9 @@ 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;