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authorDidier Pallard <didier.pallard@6wind.com>2014-02-19 17:46:08 +0100
committerThomas Monjalon <thomas.monjalon@6wind.com>2014-02-26 10:37:02 +0100
commit941b3d621e0d09553ead1429d4430e4208e832ce (patch)
treee39ccc8ae3b0febc69e50d800a11fe8f52d3de7d /lib
parent65b0663b7f32e4157b71dc14a016215e1bc63157 (diff)
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timer: add precise TSC function
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. Use r/w memory barrier instead of lfence to serialize both loads and stores. Signed-off-by: Didier Pallard <didier.pallard@6wind.com> Reviewed-by: François-Frédéric Ozog <ff@ozog.com> Reviewed-by: Konstantin Ananyev <konstantin.ananyev@intel.com> Acked-by: Thomas Monjalon <thomas.monjalon@6wind.com>
Diffstat (limited to 'lib')
-rw-r--r--lib/librte_eal/common/include/rte_cycles.h14
1 files changed, 14 insertions, 0 deletions
diff --git a/lib/librte_eal/common/include/rte_cycles.h b/lib/librte_eal/common/include/rte_cycles.h
index cc6fe71..0c19ca9 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