From: Didier Pallard <didier.pallard@6wind.com>
To: dev@dpdk.org
Subject: [dpdk-dev] [PATCH v3] timer: add new rte_rdtsc_precise function
Date: Wed, 19 Feb 2014 17:46:08 +0100 [thread overview]
Message-ID: <1392828368-8563-1-git-send-email-didier.pallard@6wind.com> (raw)
In-Reply-To: <1392809945-28025-1-git-send-email-didier.pallard@6wind.com>
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@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
next prev parent reply other threads:[~2014-02-19 16:44 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <1390562134-24720-1-git-send-email-didier.pallard@6wind.com>
2014-02-19 11:39 ` [dpdk-dev] [PATCH v2] timer: add lfence before TSC read Didier Pallard
2014-02-19 16:46 ` Didier Pallard [this message]
2014-02-26 9:39 ` [dpdk-dev] [PATCH v3] timer: add new rte_rdtsc_precise function Thomas Monjalon
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