Performance: Only dereference commit index once

[deliverable/lttng-modules.git] / lib / ringbuffer / frontend_api.h

diff --git a/lib/ringbuffer/frontend_api.h b/lib/ringbuffer/frontend_api.h
index b92ff290c300f07e90498612719fdfe190d9d79a..a6f2c6f4f16742a4b35dafaeafcc25eaa13e1a61 100644 (file)
--- a/lib/ringbuffer/frontend_api.h
+++ b/lib/ringbuffer/frontend_api.h
@@ -162,14 +162,14 @@ int lib_ring_buffer_reserve(const struct lib_ring_buffer_config *config,
        unsigned long o_begin, o_end, o_old;
        size_t before_hdr_pad = 0;
 
-       if (atomic_read(&chan->record_disabled))
+       if (unlikely(atomic_read(&chan->record_disabled)))
                return -EAGAIN;
 
        if (config->alloc == RING_BUFFER_ALLOC_PER_CPU)
                buf = per_cpu_ptr(chan->backend.buf, ctx->cpu);
        else
                buf = chan->backend.buf;
-       if (atomic_read(&buf->record_disabled))
+       if (unlikely(atomic_read(&buf->record_disabled)))
                return -EAGAIN;
        ctx->buf = buf;
 
@@ -250,6 +250,7 @@ void lib_ring_buffer_commit(const struct lib_ring_buffer_config *config,
        unsigned long offset_end = ctx->buf_offset;
        unsigned long endidx = subbuf_index(offset_end - 1, chan);
        unsigned long commit_count;
+       struct commit_counters_hot *cc_hot = &buf->commit_hot[endidx];
 
        /*
         * Must count record before incrementing the commit count.
@@ -270,7 +271,7 @@ void lib_ring_buffer_commit(const struct lib_ring_buffer_config *config,
        } else
                smp_wmb();
 
-       v_add(config, ctx->slot_size, &buf->commit_hot[endidx].cc);
+       v_add(config, ctx->slot_size, &cc_hot->cc);
 
        /*
         * commit count read can race with concurrent OOO commit count updates.
@@ -290,7 +291,7 @@ void lib_ring_buffer_commit(const struct lib_ring_buffer_config *config,
         *   count reaches back the reserve offset for a specific sub-buffer,
         *   which is completely independent of the order.
         */
-       commit_count = v_read(config, &buf->commit_hot[endidx].cc);
+       commit_count = v_read(config, &cc_hot->cc);
 
        lib_ring_buffer_check_deliver(config, buf, chan, offset_end - 1,
                                      commit_count, endidx, ctx->tsc);
@@ -298,8 +299,8 @@ void lib_ring_buffer_commit(const struct lib_ring_buffer_config *config,
         * Update used size at each commit. It's needed only for extracting
         * ring_buffer buffers from vmcore, after crash.
         */
-       lib_ring_buffer_write_commit_counter(config, buf, chan, endidx,
-                       offset_end, commit_count);
+       lib_ring_buffer_write_commit_counter(config, buf, chan,
+                       offset_end, commit_count, cc_hot);
 }
 
 /**