eal/x86: reduce contention when retrying TSX

When TSX transactions abort, it is generally worth retrying a number of
times before falling back to the traditional locking path, as the
parallelism benefits from TSX can be worth it when a transaction does
succeed. For cases with multiple threads and high contention rates, it
can be useful to have increasing delays between retry attempts, so as to
avoid having the same threads repeatedly collided.

Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>

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 60321da0249f80d12a8ac62b7b0bd0cf82fe54a9..e2e2b2643c6cd70dfc7f92f297e7f7735f27ff4f 100644 (file)
--- a/lib/librte_eal/common/include/arch/x86/rte_spinlock.h
+++ b/lib/librte_eal/common/include/arch/x86/rte_spinlock.h
@@ -15,8 +15,9 @@ extern "C" {
 #include "rte_branch_prediction.h"
 #include "rte_common.h"
 #include "rte_pause.h"
+#include "rte_cycles.h"
 
-#define RTE_RTM_MAX_RETRIES (10)
+#define RTE_RTM_MAX_RETRIES (20)
 #define RTE_XABORT_LOCK_BUSY (0xff)
 
 #ifndef RTE_FORCE_INTRINSICS
@@ -76,7 +77,7 @@ static inline int rte_tm_supported(void)
 static inline int
 rte_try_tm(volatile int *lock)
 {
-       int retries;
+       int i, retries;
 
        if (!rte_rtm_supported)
                return 0;
@@ -96,9 +97,21 @@ rte_try_tm(volatile int *lock)
                while (*lock)
                        rte_pause();
 
-               if ((status & RTE_XABORT_EXPLICIT) &&
-                       (RTE_XABORT_CODE(status) == RTE_XABORT_LOCK_BUSY))
+               if ((status & RTE_XABORT_CONFLICT) ||
+                  ((status & RTE_XABORT_EXPLICIT) &&
+                   (RTE_XABORT_CODE(status) == RTE_XABORT_LOCK_BUSY))) {
+                       /* add a small delay before retrying, basing the
+                        * delay on the number of times we've already tried,
+                        * to give a back-off type of behaviour. We
+                        * randomize trycount by taking bits from the tsc count
+                        */
+                       int try_count = RTE_RTM_MAX_RETRIES - retries;
+                       int pause_count = (rte_rdtsc() & 0x7) | 1;
+                       pause_count <<= try_count;
+                       for (i = 0; i < pause_count; i++)
+                               rte_pause();
                        continue;
+               }
 
                if ((status & RTE_XABORT_RETRY) == 0) /* do not retry */
                        break;

diff --git a/lib/librte_eal/linuxapp/eal/eal_alarm.c b/lib/librte_eal/linuxapp/eal/eal_alarm.c
index 391d2a65f0197e793d872e898d7382f4c11bca42..840ede7806645eee66a18f7cfac8b746e27c2e9e 100644 (file)
--- a/lib/librte_eal/linuxapp/eal/eal_alarm.c
+++ b/lib/librte_eal/linuxapp/eal/eal_alarm.c
@@ -30,7 +30,9 @@
 #define NS_PER_US 1000
 #define US_PER_MS 1000
 #define MS_PER_S 1000
+#ifndef US_PER_S
 #define US_PER_S (US_PER_MS * MS_PER_S)
+#endif
 
 #ifdef CLOCK_MONOTONIC_RAW /* Defined in glibc bits/time.h */
 #define CLOCK_TYPE_ID CLOCK_MONOTONIC_RAW