diff options
| -rw-r--r-- | nptl/pthreadP.h | 1 | ||||
| -rw-r--r-- | nptl/pthread_mutex_lock.c | 16 | ||||
| -rw-r--r-- | sysdeps/nptl/pthread_mutex_backoff.h | 35 | ||||
| -rw-r--r-- | sysdeps/x86_64/nptl/pthread_mutex_backoff.h | 39 |
4 files changed, 89 insertions, 2 deletions
diff --git a/nptl/pthreadP.h b/nptl/pthreadP.h index 79be1bc70f..6bc57f494f 100644 --- a/nptl/pthreadP.h +++ b/nptl/pthreadP.h @@ -35,6 +35,7 @@ #include <kernel-features.h> #include <errno.h> #include <internal-signals.h> +#include <pthread_mutex_backoff.h> #include "pthread_mutex_conf.h" diff --git a/nptl/pthread_mutex_lock.c b/nptl/pthread_mutex_lock.c index 253743f76c..16fb05a2bb 100644 --- a/nptl/pthread_mutex_lock.c +++ b/nptl/pthread_mutex_lock.c @@ -130,14 +130,26 @@ __pthread_mutex_lock (pthread_mutex_t *mutex) int cnt = 0; int max_cnt = MIN (max_adaptive_count (), mutex->__data.__spins * 2 + 10); + int spin_count, exp_backoff = 1; + unsigned int jitter = get_jitter (); do { - if (cnt++ >= max_cnt) + /* In each loop, spin count is exponential backoff plus + random jitter, random range is [0, exp_backoff-1]. */ + spin_count = exp_backoff + (jitter & (exp_backoff - 1)); + cnt += spin_count; + if (cnt >= max_cnt) { + /* If cnt exceeds max spin count, just go to wait + queue. */ LLL_MUTEX_LOCK (mutex); break; } - atomic_spin_nop (); + do + atomic_spin_nop (); + while (--spin_count > 0); + /* Prepare for next loop. */ + exp_backoff = get_next_backoff (exp_backoff); } while (LLL_MUTEX_READ_LOCK (mutex) != 0 || LLL_MUTEX_TRYLOCK (mutex) != 0); diff --git a/sysdeps/nptl/pthread_mutex_backoff.h b/sysdeps/nptl/pthread_mutex_backoff.h new file mode 100644 index 0000000000..5b26c22ac7 --- /dev/null +++ b/sysdeps/nptl/pthread_mutex_backoff.h @@ -0,0 +1,35 @@ +/* Pthread mutex backoff configuration. + Copyright (C) 2022 Free Software Foundation, Inc. + This file is part of the GNU C Library. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public + License as published by the Free Software Foundation; either + version 2.1 of the License, or (at your option) any later version. + + The GNU C Library is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library; if not, see + <https://www.gnu.org/licenses/>. */ +#ifndef _PTHREAD_MUTEX_BACKOFF_H +#define _PTHREAD_MUTEX_BACKOFF_H 1 + +static inline unsigned int +get_jitter (void) +{ + /* Arch dependent random jitter, return 0 disables random. */ + return 0; +} + +static inline int +get_next_backoff (int backoff) +{ + /* Next backoff, return 1 disables mutex backoff. */ + return 1; +} + +#endif diff --git a/sysdeps/x86_64/nptl/pthread_mutex_backoff.h b/sysdeps/x86_64/nptl/pthread_mutex_backoff.h new file mode 100644 index 0000000000..ec74c3d9db --- /dev/null +++ b/sysdeps/x86_64/nptl/pthread_mutex_backoff.h @@ -0,0 +1,39 @@ +/* Pthread mutex backoff configuration. + Copyright (C) 2022 Free Software Foundation, Inc. + This file is part of the GNU C Library. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public + License as published by the Free Software Foundation; either + version 2.1 of the License, or (at your option) any later version. + + The GNU C Library is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library; if not, see + <https://www.gnu.org/licenses/>. */ +#ifndef _PTHREAD_MUTEX_BACKOFF_H +#define _PTHREAD_MUTEX_BACKOFF_H 1 + +#include <fast-jitter.h> + +static inline unsigned int +get_jitter (void) +{ + return get_fast_jitter (); +} + +#define MAX_BACKOFF 16 + +static inline int +get_next_backoff (int backoff) +{ + /* Binary expontial backoff. Limiting max backoff + can reduce latency in large critical section. */ + return (backoff < MAX_BACKOFF) ? backoff << 1 : backoff; +} + +#endif |