* [dpdk-dev] [PATCH v2] timer: add lfence before TSC read
[not found] <1390562134-24720-1-git-send-email-didier.pallard@6wind.com>
@ 2014-02-19 11:39 ` Didier Pallard
2014-02-19 16:46 ` [dpdk-dev] [PATCH v3] timer: add new rte_rdtsc_precise function Didier Pallard
0 siblings, 1 reply; 3+ messages in thread
From: Didier Pallard @ 2014-02-19 11:39 UTC (permalink / raw)
To: thomas.monjalon
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 lfence instruction before rdtsc to
synchronize read operations and ensure that the TSC read is done at the expected
place.
Signed-off-by: Didier Pallard <didier.pallard@6wind.com>
---
Introduce a rte_rdtsc_precise function that adds lfence before reading tsc counter.
lib/librte_eal/common/include/rte_cycles.h | 37 ++++++++++++++++++++++++++++
1 file changed, 37 insertions(+)
diff --git a/lib/librte_eal/common/include/rte_cycles.h b/lib/librte_eal/common/include/rte_cycles.h
index cc6fe71..662f62d 100644
--- a/lib/librte_eal/common/include/rte_cycles.h
+++ b/lib/librte_eal/common/include/rte_cycles.h
@@ -128,6 +128,43 @@ 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)
+{
+ union {
+ uint64_t tsc_64;
+ struct {
+ uint32_t lo_32;
+ uint32_t hi_32;
+ };
+ } tsc;
+
+ /* serialize previous load instructions in pipe */
+ asm volatile("lfence");
+
+#ifdef RTE_LIBRTE_EAL_VMWARE_TSC_MAP_SUPPORT
+ if (unlikely(rte_cycles_vmware_tsc_map)) {
+ /* ecx = 0x10000 corresponds to the physical TSC for VMware */
+ asm volatile("rdpmc" :
+ "=a" (tsc.lo_32),
+ "=d" (tsc.hi_32) :
+ "c"(0x10000));
+ return tsc.tsc_64;
+ }
+#endif
+
+ asm volatile("rdtsc" :
+ "=a" (tsc.lo_32),
+ "=d" (tsc.hi_32));
+ return tsc.tsc_64;
+}
+
+/**
* Get the measured frequency of the RDTSC counter
*
* @return
--
1.7.10.4
^ permalink raw reply [flat|nested] 3+ messages in thread
* [dpdk-dev] [PATCH v3] timer: add new rte_rdtsc_precise function
2014-02-19 11:39 ` [dpdk-dev] [PATCH v2] timer: add lfence before TSC read Didier Pallard
@ 2014-02-19 16:46 ` Didier Pallard
2014-02-26 9:39 ` Thomas Monjalon
0 siblings, 1 reply; 3+ messages in thread
From: Didier Pallard @ 2014-02-19 16:46 UTC (permalink / raw)
To: dev
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
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [dpdk-dev] [PATCH v3] timer: add new rte_rdtsc_precise function
2014-02-19 16:46 ` [dpdk-dev] [PATCH v3] timer: add new rte_rdtsc_precise function Didier Pallard
@ 2014-02-26 9:39 ` Thomas Monjalon
0 siblings, 0 replies; 3+ messages in thread
From: Thomas Monjalon @ 2014-02-26 9:39 UTC (permalink / raw)
To: Didier Pallard; +Cc: dev
19/02/2014 17:46, Didier Pallard:
> 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.
Acked and applied.
Thanks to all
--
Thomas
^ permalink raw reply [flat|nested] 3+ messages in thread
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2014-02-19 11:39 ` [dpdk-dev] [PATCH v2] timer: add lfence before TSC read Didier Pallard
2014-02-19 16:46 ` [dpdk-dev] [PATCH v3] timer: add new rte_rdtsc_precise function Didier Pallard
2014-02-26 9:39 ` Thomas Monjalon
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