[dpdk-dev] [PATCH v3] timer: add new rte_rdtsc_precise function

Didier Pallard didier.pallard at 6wind.com
Wed Feb 19 17:46:08 CET 2014

According to Intel Developer's Manual:

"The RDTSC instruction is not a serializing instruction. It does not necessarily wait
 until all previous instructions have been executed before reading the counter. Simi-
 larly, subsequent instructions may begin execution before the read operation is
 performed. If software requires RDTSC to be executed only after all previous instruc-
 tions have completed locally, it can either use RDTSCP (if the processor supports that
 instruction) or execute the sequence LFENCE;RDTSC."

So add a rte_rdtsc_precise function that do a memory barrier before rdtsc to
synchronize operations and ensure that the TSC read is done at the expected

Signed-off-by: Didier Pallard <didier.pallard at 6wind.com>

Call rte_mb() and rte_rdtsc() rather than duplicating rte_rdtsc function.
Use r/w memory barrier instead of lfence to serialize both load and stores.

 lib/librte_eal/common/include/rte_cycles.h |   14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/lib/librte_eal/common/include/rte_cycles.h b/lib/librte_eal/common/include/rte_cycles.h
index cc6fe71..e91edf8 100644
--- a/lib/librte_eal/common/include/rte_cycles.h
+++ b/lib/librte_eal/common/include/rte_cycles.h
@@ -76,6 +76,7 @@ extern "C" {
 #include <stdint.h>
 #include <rte_debug.h>
+#include <rte_atomic.h>
 /** Global switch to use VMWARE mapping of TSC instead of RDTSC */
@@ -128,6 +129,19 @@ rte_rdtsc(void)
+ * Read the TSC register precisely where function is called.
+ *
+ * @return
+ *   The TSC for this lcore.
+ */
+static inline uint64_t
+	rte_mb();
+	return(rte_rdtsc());
  * Get the measured frequency of the RDTSC counter
  * @return

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