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
place.
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>
#ifdef RTE_LIBRTE_EAL_VMWARE_TSC_MAP_SUPPORT
/** 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_rdtsc_precise(void)
+{
+ rte_mb();
+ return(rte_rdtsc());
+}
+
+/**
* Get the measured frequency of the RDTSC counter
*
* @return
--
1.7.10.4
