Remove unneeded signal-based MB from QSBR rcu

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>

diff --git a/urcu-qsbr.c b/urcu-qsbr.c
index fd0ebf6c4a710ae2bed98e6a919f424eb05bc992..48bc62ec25e09e18395970d591f9dc64b57a1ed7 100644 (file)
--- a/urcu-qsbr.c
+++ b/urcu-qsbr.c
@@ -36,11 +36,6 @@
 /* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
 #include "urcu.h"
 
-void __attribute__((constructor)) urcu_init(void);
-void __attribute__((destructor)) urcu_exit(void);
-
-int init_done;
-
 pthread_mutex_t urcu_mutex = PTHREAD_MUTEX_INITIALIZER;
 
 /*
@@ -110,7 +105,6 @@ void internal_urcu_unlock(void)
        }
 }
 
-#ifdef DEBUG_FULL_MB
 #ifdef HAS_INCOHERENT_CACHES
 static void force_mb_single_thread(struct reader_registry *index)
 {
@@ -122,74 +116,6 @@ static void force_mb_all_threads(void)
 {
        smp_mb();
 }
-#else /* #ifdef DEBUG_FULL_MB */
-#ifdef HAS_INCOHERENT_CACHES
-static void force_mb_single_thread(struct reader_registry *index)
-{
-       assert(registry);
-       /*
-        * pthread_kill has a smp_mb(). But beware, we assume it performs
-        * a cache flush on architectures with non-coherent cache. Let's play
-        * safe and don't assume anything : we use smp_mc() to make sure the
-        * cache flush is enforced.
-        */
-       *index->need_mb = 1;
-       smp_mc();       /* write ->need_mb before sending the signals */
-       pthread_kill(index->tid, SIGURCU);
-       smp_mb();
-       /*
-        * Wait for sighandler (and thus mb()) to execute on every thread.
-        * BUSY-LOOP.
-        */
-       while (*index->need_mb) {
-               poll(NULL, 0, 1);
-       }
-       smp_mb();       /* read ->need_mb before ending the barrier */
-}
-#endif /* #ifdef HAS_INCOHERENT_CACHES */
-
-static void force_mb_all_threads(void)
-{
-       struct reader_registry *index;
-       /*
-        * Ask for each threads to execute a smp_mb() so we can consider the
-        * compiler barriers around rcu read lock as real memory barriers.
-        */
-       if (!registry)
-               return;
-       /*
-        * pthread_kill has a smp_mb(). But beware, we assume it performs
-        * a cache flush on architectures with non-coherent cache. Let's play
-        * safe and don't assume anything : we use smp_mc() to make sure the
-        * cache flush is enforced.
-        */
-       for (index = registry; index < registry + num_readers; index++) {
-               *index->need_mb = 1;
-               smp_mc();       /* write need_mb before sending the signal */
-               pthread_kill(index->tid, SIGURCU);
-       }
-       /*
-        * Wait for sighandler (and thus mb()) to execute on every thread.
-        *
-        * Note that the pthread_kill() will never be executed on systems
-        * that correctly deliver signals in a timely manner.  However, it
-        * is not uncommon for kernels to have bugs that can result in
-        * lost or unduly delayed signals.
-        *
-        * If you are seeing the below pthread_kill() executing much at
-        * all, we suggest testing the underlying kernel and filing the
-        * relevant bug report.  For Linux kernels, we recommend getting
-        * the Linux Test Project (LTP).
-        */
-       for (index = registry; index < registry + num_readers; index++) {
-               while (*index->need_mb) {
-                       pthread_kill(index->tid, SIGURCU);
-                       poll(NULL, 0, 1);
-               }
-       }
-       smp_mb();       /* read ->need_mb before ending the barrier */
-}
-#endif /* #else #ifdef DEBUG_FULL_MB */
 
 void wait_for_quiescent_state(void)
 {
@@ -324,7 +250,6 @@ static void rcu_remove_reader(pthread_t id)
 void rcu_register_thread(void)
 {
        internal_urcu_lock();
-       urcu_init();    /* In case gcc does not support constructor attribute */
        rcu_add_reader(pthread_self());
        internal_urcu_unlock();
 }
@@ -335,56 +260,3 @@ void rcu_unregister_thread(void)
        rcu_remove_reader(pthread_self());
        internal_urcu_unlock();
 }
-
-#ifndef DEBUG_FULL_MB
-static void sigurcu_handler(int signo, siginfo_t *siginfo, void *context)
-{
-       /*
-        * Executing this smp_mb() is the only purpose of this signal handler.
-        * It punctually promotes barrier() into smp_mb() on every thread it is
-        * executed on.
-        */
-       smp_mb();
-       need_mb = 0;
-       smp_mb();
-}
-
-/*
- * urcu_init constructor. Called when the library is linked, but also when
- * reader threads are calling rcu_register_thread().
- * Should only be called by a single thread at a given time. This is ensured by
- * holing the internal_urcu_lock() from rcu_register_thread() or by running at
- * library load time, which should not be executed by multiple threads nor
- * concurrently with rcu_register_thread() anyway.
- */
-void urcu_init(void)
-{
-       struct sigaction act;
-       int ret;
-
-       if (init_done)
-               return;
-       init_done = 1;
-
-       act.sa_sigaction = sigurcu_handler;
-       ret = sigaction(SIGURCU, &act, NULL);
-       if (ret) {
-               perror("Error in sigaction");
-               exit(-1);
-       }
-}
-
-void urcu_exit(void)
-{
-       struct sigaction act;
-       int ret;
-
-       ret = sigaction(SIGURCU, NULL, &act);
-       if (ret) {
-               perror("Error in sigaction");
-               exit(-1);
-       }
-       assert(act.sa_sigaction == sigurcu_handler);
-       free(registry);
-}
-#endif /* #ifndef DEBUG_FULL_MB */

diff --git a/urcu-qsbr.h b/urcu-qsbr.h
index 101b94d49d83c71230bf208bf5cd9771656bab5b..59621807abf470012bc94ee48cc7e6ee786d2b65 100644 (file)
--- a/urcu-qsbr.h
+++ b/urcu-qsbr.h
@@ -117,13 +117,8 @@
 #define YIELD_READ     (1 << 0)
 #define YIELD_WRITE    (1 << 1)
 
-/* Updates without DEBUG_FULL_MB are much slower. Account this in the delay */
-#ifdef DEBUG_FULL_MB
 /* maximum sleep delay, in us */
 #define MAX_SLEEP 50
-#else
-#define MAX_SLEEP 30000
-#endif
 
 extern unsigned int yield_active;
 extern unsigned int __thread rand_yield;
@@ -161,17 +156,10 @@ static inline void debug_yield_init(void)
 }
 #endif
 
-#ifdef DEBUG_FULL_MB
 static inline void reader_barrier()
 {
        smp_mb();
 }
-#else
-static inline void reader_barrier()
-{
-       barrier();
-}
-#endif
 
 /*
  * The trick here is that RCU_GP_CTR_BIT must be a multiple of 8 so we can use a