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authorDave Barach <dave@barachs.net>2019-02-19 17:05:30 -0500
committerDamjan Marion <dmarion@me.com>2019-02-20 16:27:47 +0000
commita4324a996f34902579338033110d27575a654c8e (patch)
treecdc4a58a8d055053cf8ef90b5ddf7d0fcd1a5af2
parent51a423dc2b0d4aad0bbd8f7e757d2ca49221ff83 (diff)
calculate per-thread time offset
The main thread squirrels away vlib_time_now (&vlib_global_main), worker threads use it to calculate an offset in f64 seconds from their own vlib_time_now(vm) value. We use that offset until the next barrier sync. Thanks to Damjan for the suggestion. Change-Id: If56cdfe68e5ad8ac3b0d0fc885dc3ba556cd1215 Signed-off-by: Dave Barach <dave@barachs.net>
-rw-r--r--src/vlib/main.h5
-rw-r--r--src/vlib/threads.c47
-rw-r--r--src/vlib/threads.h15
3 files changed, 66 insertions, 1 deletions
diff --git a/src/vlib/main.h b/src/vlib/main.h
index f89ecd3299f..4192c3f2720 100644
--- a/src/vlib/main.h
+++ b/src/vlib/main.h
@@ -63,6 +63,9 @@ typedef struct vlib_main_t
CLIB_CACHE_LINE_ALIGN_MARK (cacheline0);
/* Instruction level timing state. */
clib_time_t clib_time;
+ /* Offset from main thread time */
+ f64 time_offset;
+ f64 time_last_barrier_release;
/* Time stamp of last node dispatch. */
u64 cpu_time_last_node_dispatch;
@@ -232,7 +235,7 @@ void vlib_worker_loop (vlib_main_t * vm);
always_inline f64
vlib_time_now (vlib_main_t * vm)
{
- return clib_time_now (&vm->clib_time);
+ return clib_time_now (&vm->clib_time) + vm->time_offset;
}
always_inline f64
diff --git a/src/vlib/threads.c b/src/vlib/threads.c
index cdb4eb082b5..4368a74ac9f 100644
--- a/src/vlib/threads.c
+++ b/src/vlib/threads.c
@@ -1510,6 +1510,14 @@ vlib_worker_thread_barrier_release (vlib_main_t * vm)
deadline = now + BARRIER_SYNC_TIMEOUT;
+ /*
+ * Note when we let go of the barrier.
+ * Workers can use this to derive a reasonably accurate
+ * time offset. See vlib_time_now(...)
+ */
+ vm->time_last_barrier_release = vlib_time_now (vm);
+ CLIB_MEMORY_STORE_BARRIER ();
+
*vlib_worker_threads->wait_at_barrier = 0;
while (*vlib_worker_threads->workers_at_barrier > 0)
@@ -1808,6 +1816,45 @@ threads_init (vlib_main_t * vm)
VLIB_INIT_FUNCTION (threads_init);
+
+static clib_error_t *
+show_clock_command_fn (vlib_main_t * vm,
+ unformat_input_t * input, vlib_cli_command_t * cmd)
+{
+ int i;
+ f64 now;
+
+ now = vlib_time_now (vm);
+
+ vlib_cli_output (vm, "Time now %.9f", now);
+
+ if (vec_len (vlib_mains) == 1)
+ return 0;
+
+ vlib_cli_output (vm, "Time last barrier release %.9f",
+ vm->time_last_barrier_release);
+
+ for (i = 1; i < vec_len (vlib_mains); i++)
+ {
+ if (vlib_mains[i] == 0)
+ continue;
+ vlib_cli_output (vm, "Thread %d offset %.9f error %.9f", i,
+ vlib_mains[i]->time_offset,
+ vm->time_last_barrier_release -
+ vlib_mains[i]->time_last_barrier_release);
+ }
+ return 0;
+}
+
+/* *INDENT-OFF* */
+VLIB_CLI_COMMAND (f_command, static) =
+{
+ .path = "show clock",
+ .short_help = "show clock",
+ .function = show_clock_command_fn,
+};
+/* *INDENT-ON* */
+
/*
* fd.io coding-style-patch-verification: ON
*
diff --git a/src/vlib/threads.h b/src/vlib/threads.h
index 0e9cba52103..95fcf3d83d7 100644
--- a/src/vlib/threads.h
+++ b/src/vlib/threads.h
@@ -422,6 +422,21 @@ vlib_worker_thread_barrier_check (void)
}
while (*vlib_worker_threads->wait_at_barrier)
;
+
+ /*
+ * Recompute the offset from thread-0 time.
+ * Note that vlib_time_now adds vm->time_offset, so
+ * clear it first. Save the resulting idea of "now", to
+ * see how well we're doing. See show_clock_command_fn(...)
+ */
+ {
+ f64 now;
+ vm->time_offset = 0.0;
+ now = vlib_time_now (vm);
+ vm->time_offset = vlib_global_main.time_last_barrier_release - now;
+ vm->time_last_barrier_release = vlib_time_now (vm);
+ }
+
if (CLIB_DEBUG > 0)
vm->parked_at_barrier = 0;
clib_atomic_fetch_add (vlib_worker_threads->workers_at_barrier, -1);