Use rseq for reserve position

[lttng-ust.git] / liblttng-ust / lttng-ring-buffer-client.h

diff --git a/liblttng-ust/lttng-ring-buffer-client.h b/liblttng-ust/lttng-ring-buffer-client.h
index 5fde855cea6947bc1f24f0a2d75388d777930298..f014f4e46158e9706873e9ae5bc7a74d67a72303 100644 (file)
--- a/liblttng-ust/lttng-ring-buffer-client.h
+++ b/liblttng-ust/lttng-ring-buffer-client.h
@@ -637,7 +637,7 @@ static const struct lttng_ust_lib_ring_buffer_config client_config = {
 
        .tsc_bits = LTTNG_COMPACT_TSC_BITS,
        .alloc = RING_BUFFER_ALLOC_PER_CPU,
-       .sync = RING_BUFFER_SYNC_GLOBAL,
+       .sync = RING_BUFFER_SYNC_PER_CPU,
        .mode = RING_BUFFER_MODE_TEMPLATE,
        .backend = RING_BUFFER_PAGE,
        .output = RING_BUFFER_MMAP,
@@ -696,7 +696,7 @@ int lttng_event_reserve(struct lttng_ust_lib_ring_buffer_ctx *ctx,
 {
        struct lttng_channel *lttng_chan = channel_get_private(ctx->chan);
        struct lttng_rseq_state rseq_state;
-       int ret, cpu;
+       int ret, cpu, fallback = 0;
 
        if (lib_ring_buffer_begin(&client_config))
                return -EPERM;
@@ -716,6 +716,7 @@ retry:
        } else {
                cpu = rseq_cpu_at_start(rseq_state);
        }
+fallback:
        ctx->cpu = cpu;
 
        switch (lttng_chan->header_type) {
@@ -731,9 +732,25 @@ retry:
                WARN_ON_ONCE(1);
        }
 
+       if (caa_likely(ctx->ctx_len
+                       >= sizeof(struct lttng_ust_lib_ring_buffer_ctx)))
+               ctx->rseq_state = rseq_state;
+
        ret = lib_ring_buffer_reserve(&client_config, ctx);
-       if (caa_unlikely(ret))
-               goto put;
+       if (caa_unlikely(ret)) {
+               if (ret == -EAGAIN) {
+                       assert(!fallback);
+                       fallback = 1;
+                       uatomic_inc(&lttng_chan->chan->u.reserve_fallback_ref);
+                       cpu = lib_ring_buffer_get_cpu(&client_config);
+                       if (caa_unlikely(cpu < 0)) {
+                               ret = -EPERM;
+                               goto end;
+                       }
+                       goto fallback;
+               }
+               goto end;
+       }
        if (caa_likely(ctx->ctx_len
                        >= sizeof(struct lttng_ust_lib_ring_buffer_ctx))) {
                if (lib_ring_buffer_backend_get_pages(&client_config, ctx,
@@ -744,13 +761,14 @@ retry:
        }
        lttng_write_event_header(&client_config, ctx, event_id);
 
-       if (caa_likely(ctx->ctx_len
-                       >= sizeof(struct lttng_ust_lib_ring_buffer_ctx)))
-               ctx->rseq_state = rseq_state;
+       if (caa_unlikely(fallback))
+               uatomic_dec(&lttng_chan->chan->u.reserve_fallback_ref);
 
        return 0;
 end:
        lib_ring_buffer_end(&client_config);
+       if (fallback)
+               uatomic_dec(&lttng_chan->chan->u.reserve_fallback_ref);
        return ret;
 }