[dpdk-dev] [PATCH v2 1/3] spinlock: add support for HTM lock elision for x86

[Roman Dementiev <roman.dementiev@intel.com>]

This patch adds methods that use hardware memory transactions (HTM) on fast-path
for spinlocks (a.k.a. lock elision). Here the methods are implemented for x86
using Restricted Transactional Memory instructions (Intel(r) Transactional
Synchronization Extensions). The implementation fall-backs to the normal
spinlock if HTM is not available or memory transactions fail. This is not
a replacement for all spinlock usages since not all critical sections protected
by spinlocks are friendly to HTM. For example, an attempt to perform a HW I/O
operation inside a hardware memory transaction always aborts the transaction
since the CPU is not able to roll-back should the transaction fail.
Therefore, hardware transactional locks are not advised to be used around
rte_eth_rx_burst() and rte_eth_tx_burst() calls.

Signed-off-by: Roman Dementiev <roman.dementiev@intel.com>
---
 .../common/include/arch/ppc_64/rte_spinlock.h      |  41 ++++++++
 lib/librte_eal/common/include/arch/x86/rte_rtm.h   |  73 ++++++++++++++
 .../common/include/arch/x86/rte_spinlock.h         | 107 +++++++++++++++++++++
 .../common/include/generic/rte_spinlock.h          |  99 +++++++++++++++++++
 4 files changed, 320 insertions(+)
 create mode 100644 lib/librte_eal/common/include/arch/x86/rte_rtm.h

diff --git a/lib/librte_eal/common/include/arch/ppc_64/rte_spinlock.h b/lib/librte_eal/common/include/arch/ppc_64/rte_spinlock.h
index cf8b81a..3336435 100644
--- a/lib/librte_eal/common/include/arch/ppc_64/rte_spinlock.h
+++ b/lib/librte_eal/common/include/arch/ppc_64/rte_spinlock.h
@@ -66,6 +66,47 @@ rte_spinlock_trylock(rte_spinlock_t *sl)
 
 #endif
 
+static inline int rte_tm_supported(void)
+{
+	return 0;
+}
+
+static inline void
+rte_spinlock_lock_tm(rte_spinlock_t *sl)
+{
+	rte_spinlock_lock(sl); /* fall-back */
+}
+
+static inline int
+rte_spinlock_trylock_tm(rte_spinlock_t *sl)
+{
+	return rte_spinlock_trylock(sl);
+}
+
+static inline void
+rte_spinlock_unlock_tm(rte_spinlock_t *sl)
+{
+	rte_spinlock_unlock(sl);
+}
+
+static inline void
+rte_spinlock_recursive_lock_tm(rte_spinlock_recursive_t *slr)
+{
+	rte_spinlock_recursive_lock(slr); /* fall-back */
+}
+
+static inline void
+rte_spinlock_recursive_unlock_tm(rte_spinlock_recursive_t *slr)
+{
+	rte_spinlock_recursive_unlock(slr);
+}
+
+static inline int
+rte_spinlock_recursive_trylock_tm(rte_spinlock_recursive_t *slr)
+{
+	return rte_spinlock_recursive_trylock(slr);
+}
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/lib/librte_eal/common/include/arch/x86/rte_rtm.h b/lib/librte_eal/common/include/arch/x86/rte_rtm.h
new file mode 100644
index 0000000..d935641
--- /dev/null
+++ b/lib/librte_eal/common/include/arch/x86/rte_rtm.h
@@ -0,0 +1,73 @@
+#ifndef _RTE_RTM_H_
+#define _RTE_RTM_H_ 1
+
+/*
+ * Copyright (c) 2012,2013 Intel Corporation
+ * Author: Andi Kleen
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that: (1) source code distributions
+ * retain the above copyright notice and this paragraph in its entirety, (2)
+ * distributions including binary code include the above copyright notice and
+ * this paragraph in its entirety in the documentation or other materials
+ * provided with the distribution
+ *
+ * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
+ * WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
+ */
+
+/* Official RTM intrinsics interface matching gcc/icc, but works
+   on older gcc compatible compilers and binutils. */
+
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+
+#define RTE_XBEGIN_STARTED		(~0u)
+#define RTE_XABORT_EXPLICIT		(1 << 0)
+#define RTE_XABORT_RETRY		(1 << 1)
+#define RTE_XABORT_CONFLICT		(1 << 2)
+#define RTE_XABORT_CAPACITY		(1 << 3)
+#define RTE_XABORT_DEBUG		(1 << 4)
+#define RTE_XABORT_NESTED		(1 << 5)
+#define RTE_XABORT_CODE(x)		(((x) >> 24) & 0xff)
+
+static __attribute__((__always_inline__)) inline
+unsigned int rte_xbegin(void)
+{
+	unsigned int ret = RTE_XBEGIN_STARTED;
+
+	asm volatile(".byte 0xc7,0xf8 ; .long 0" : "+a" (ret) :: "memory");
+	return ret;
+}
+
+static __attribute__((__always_inline__)) inline
+void rte_xend(void)
+{
+	 asm volatile(".byte 0x0f,0x01,0xd5" ::: "memory");
+}
+
+static __attribute__((__always_inline__)) inline
+void rte_xabort(const unsigned int status)
+{
+	asm volatile(".byte 0xc6,0xf8,%P0" :: "i" (status) : "memory");
+}
+
+static __attribute__((__always_inline__)) inline
+int rte_xtest(void)
+{
+	unsigned char out;
+
+	asm volatile(".byte 0x0f,0x01,0xd6 ; setnz %0" :
+		"=r" (out) :: "memory");
+	return out;
+}
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* _RTE_RTM_H_ */
diff --git a/lib/librte_eal/common/include/arch/x86/rte_spinlock.h b/lib/librte_eal/common/include/arch/x86/rte_spinlock.h
index 54fba95..136f25a 100644
--- a/lib/librte_eal/common/include/arch/x86/rte_spinlock.h
+++ b/lib/librte_eal/common/include/arch/x86/rte_spinlock.h
@@ -39,6 +39,13 @@ extern "C" {
 #endif
 
 #include "generic/rte_spinlock.h"
+#include "rte_rtm.h"
+#include "rte_cpuflags.h"
+#include "rte_branch_prediction.h"
+#include <rte_common.h>
+
+#define RTE_RTM_MAX_RETRIES (10)
+#define RTE_XABORT_LOCK_BUSY (0xff)
 
 #ifndef RTE_FORCE_INTRINSICS
 static inline void
@@ -87,6 +94,106 @@ rte_spinlock_trylock (rte_spinlock_t *sl)
 }
 #endif
 
+static uint8_t rtm_supported; /* cache the flag to avoid the overhead
+				 of the rte_cpu_get_flag_enabled function */
+
+static inline void __attribute__((constructor))
+rte_rtm_init(void)
+{
+	rtm_supported = rte_cpu_get_flag_enabled(RTE_CPUFLAG_RTM);
+}
+
+static inline int rte_tm_supported(void)
+{
+	return rtm_supported;
+}
+
+static inline int
+rte_try_tm(volatile int *lock)
+{
+	if (!rtm_supported)
+		return 0;
+
+	int retries = RTE_RTM_MAX_RETRIES;
+
+	while (likely(retries--)) {
+
+		unsigned int status = rte_xbegin();
+
+		if (likely(RTE_XBEGIN_STARTED == status)) {
+			if (unlikely(*lock))
+				rte_xabort(RTE_XABORT_LOCK_BUSY);
+			else
+				return 1;
+		}
+		while (*lock)
+			rte_pause();
+
+		if ((status & RTE_XABORT_EXPLICIT) &&
+			(RTE_XABORT_CODE(status) == RTE_XABORT_LOCK_BUSY))
+			continue;
+
+		if ((status & RTE_XABORT_RETRY) == 0) /* do not retry */
+			break;
+	}
+	return 0;
+}
+
+static inline void
+rte_spinlock_lock_tm(rte_spinlock_t *sl)
+{
+	if (likely(rte_try_tm(&sl->locked)))
+		return;
+
+	rte_spinlock_lock(sl); /* fall-back */
+}
+
+static inline int
+rte_spinlock_trylock_tm(rte_spinlock_t *sl)
+{
+	if (likely(rte_try_tm(&sl->locked)))
+		return 1;
+
+	return rte_spinlock_trylock(sl);
+}
+
+static inline void
+rte_spinlock_unlock_tm(rte_spinlock_t *sl)
+{
+	if (unlikely(sl->locked))
+		rte_spinlock_unlock(sl);
+	else
+		rte_xend();
+}
+
+static inline void
+rte_spinlock_recursive_lock_tm(rte_spinlock_recursive_t *slr)
+{
+	if (likely(rte_try_tm(&slr->sl.locked)))
+		return;
+
+	rte_spinlock_recursive_lock(slr); /* fall-back */
+}
+
+static inline void
+rte_spinlock_recursive_unlock_tm(rte_spinlock_recursive_t *slr)
+{
+	if (unlikely(slr->sl.locked))
+		rte_spinlock_recursive_unlock(slr);
+	else
+		rte_xend();
+}
+
+static inline int
+rte_spinlock_recursive_trylock_tm(rte_spinlock_recursive_t *slr)
+{
+	if (likely(rte_try_tm(&slr->sl.locked)))
+		return 1;
+
+	return rte_spinlock_recursive_trylock(slr);
+}
+
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/lib/librte_eal/common/include/generic/rte_spinlock.h b/lib/librte_eal/common/include/generic/rte_spinlock.h
index c7fb0df..4e0a3c3 100644
--- a/lib/librte_eal/common/include/generic/rte_spinlock.h
+++ b/lib/librte_eal/common/include/generic/rte_spinlock.h
@@ -145,6 +145,59 @@ static inline int rte_spinlock_is_locked (rte_spinlock_t *sl)
 }
 
 /**
+ * Test if hardware transactional memory (lock elision) is supported
+ *
+ * @return
+ *   1 if the hardware transactional memory is supported; 0 otherwise.
+ */
+static inline int rte_tm_supported(void);
+
+/**
+ * Try to execute critical section in a hardware memory transaction,
+ * if it fails or not available take the spinlock.
+ *
+ * NOTE: An attempt to perform a HW I/O operation inside a hardware memory
+ * transaction always aborts the transaction since the CPU is not able to
+ * roll-back should the transaction fail. Therefore, hardware transactional
+ * locks are not advised to be used around rte_eth_rx_burst() and
+ * rte_eth_tx_burst() calls.
+ *
+ * @param sl
+ *   A pointer to the spinlock.
+ */
+static inline void
+rte_spinlock_lock_tm(rte_spinlock_t *sl);
+
+/**
+ * Commit hardware memory transaction or release the spinlock if
+ * the spinlock is used as a fall-back
+ *
+ * @param sl
+ *   A pointer to the spinlock.
+ */
+static inline void
+rte_spinlock_unlock_tm(rte_spinlock_t *sl);
+
+/**
+ * Try to execute critical section in a hardware memory transaction,
+ * if it fails or not available try to take the lock.
+ *
+ * NOTE: An attempt to perform a HW I/O operation inside a hardware memory
+ * transaction always aborts the transaction since the CPU is not able to
+ * roll-back should the transaction fail. Therefore, hardware transactional
+ * locks are not advised to be used around rte_eth_rx_burst() and
+ * rte_eth_tx_burst() calls.
+ *
+ * @param sl
+ *   A pointer to the spinlock.
+ * @return
+ *   1 if the hardware memory transaction is successfully started
+ *   or lock is successfully taken; 0 otherwise.
+ */
+static inline int
+rte_spinlock_trylock_tm(rte_spinlock_t *sl);
+
+/**
  * The rte_spinlock_recursive_t type.
  */
 typedef struct {
@@ -223,4 +276,50 @@ static inline int rte_spinlock_recursive_trylock(rte_spinlock_recursive_t *slr)
 	return 1;
 }
 
+
+/**
+ * Try to execute critical section in a hardware memory transaction,
+ * if it fails or not available take the recursive spinlocks
+ *
+ * NOTE: An attempt to perform a HW I/O operation inside a hardware memory
+ * transaction always aborts the transaction since the CPU is not able to
+ * roll-back should the transaction fail. Therefore, hardware transactional
+ * locks are not advised to be used around rte_eth_rx_burst() and
+ * rte_eth_tx_burst() calls.
+ *
+ * @param slr
+ *   A pointer to the recursive spinlock.
+ */
+static inline void rte_spinlock_recursive_lock_tm(
+	rte_spinlock_recursive_t *slr);
+
+/**
+ * Commit hardware memory transaction or release the recursive spinlock
+ * if the recursive spinlock is used as a fall-back
+ *
+ * @param slr
+ *   A pointer to the recursive spinlock.
+ */
+static inline void rte_spinlock_recursive_unlock_tm(
+	rte_spinlock_recursive_t *slr);
+
+/**
+ * Try to execute critical section in a hardware memory transaction,
+ * if it fails or not available try to take the recursive lock
+ *
+ * NOTE: An attempt to perform a HW I/O operation inside a hardware memory
+ * transaction always aborts the transaction since the CPU is not able to
+ * roll-back should the transaction fail. Therefore, hardware transactional
+ * locks are not advised to be used around rte_eth_rx_burst() and
+ * rte_eth_tx_burst() calls.
+ *
+ * @param slr
+ *   A pointer to the recursive spinlock.
+ * @return
+ *   1 if the hardware memory transaction is successfully started
+ *   or lock is successfully taken; 0 otherwise.
+ */
+static inline int rte_spinlock_recursive_trylock_tm(
+	rte_spinlock_recursive_t *slr);
+
 #endif /* _RTE_SPINLOCK_H_ */
-- 
1.9.5.msysgit.0

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