From: Mathieu Desnoyers Date: Wed, 10 Jun 2009 14:17:35 +0000 (-0400) Subject: Remove unneeded signal-based MB from QSBR rcu X-Git-Tag: v0.1~180 X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=656c6da75f7ee119bfc49e026f52d695d0d1aea2;p=urcu.git Remove unneeded signal-based MB from QSBR rcu Signed-off-by: Mathieu Desnoyers --- diff --git a/urcu-qsbr.c b/urcu-qsbr.c index fd0ebf6..48bc62e 100644 --- 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 101b94d..5962180 100644 --- 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