From ca6e601a9d4a72b3699cca15bad12ac1716bf49a Mon Sep 17 00:00:00 2001 From: Torvald Riegel Date: Wed, 30 Nov 2016 17:53:11 +0100 Subject: Use C11-like atomics instead of plain memory accesses in x86 lock elision. This uses atomic operations to access lock elision metadata that is accessed concurrently (ie, adapt_count fields). The size of the data is less than a word but accessed only with atomic loads and stores; therefore, we add support for shorter-size atomic load and stores too. * include/atomic.h (__atomic_check_size_ls): New. (atomic_load_relaxed, atomic_load_acquire, atomic_store_relaxed, atomic_store_release): Use it. * sysdeps/x86/elide.h (ACCESS_ONCE): Remove. (elision_adapt, ELIDE_LOCK): Use atomics. * sysdeps/unix/sysv/linux/x86/elision-lock.c (__lll_lock_elision): Use atomics and improve code comments. * sysdeps/unix/sysv/linux/x86/elision-trylock.c (__lll_trylock_elision): Likewise. --- include/atomic.h | 24 ++++++++++++++++++++---- 1 file changed, 20 insertions(+), 4 deletions(-) (limited to 'include') diff --git a/include/atomic.h b/include/atomic.h index c8b46649c5..d14cbc5ca8 100644 --- a/include/atomic.h +++ b/include/atomic.h @@ -550,6 +550,20 @@ void __atomic_link_error (void); if (sizeof (*mem) != 4) \ __atomic_link_error (); # endif +/* We additionally provide 8b and 16b atomic loads and stores; we do not yet + need other atomic operations of such sizes, and restricting the support to + loads and stores makes this easier for archs that do not have native + support for atomic operations to less-than-word-sized data. */ +# if __HAVE_64B_ATOMICS == 1 +# define __atomic_check_size_ls(mem) \ + if ((sizeof (*mem) != 1) && (sizeof (*mem) != 2) && (sizeof (*mem) != 4) \ + && (sizeof (*mem) != 8)) \ + __atomic_link_error (); +# else +# define __atomic_check_size_ls(mem) \ + if ((sizeof (*mem) != 1) && (sizeof (*mem) != 2) && sizeof (*mem) != 4) \ + __atomic_link_error (); +# endif # define atomic_thread_fence_acquire() \ __atomic_thread_fence (__ATOMIC_ACQUIRE) @@ -559,18 +573,20 @@ void __atomic_link_error (void); __atomic_thread_fence (__ATOMIC_SEQ_CST) # define atomic_load_relaxed(mem) \ - ({ __atomic_check_size((mem)); __atomic_load_n ((mem), __ATOMIC_RELAXED); }) + ({ __atomic_check_size_ls((mem)); \ + __atomic_load_n ((mem), __ATOMIC_RELAXED); }) # define atomic_load_acquire(mem) \ - ({ __atomic_check_size((mem)); __atomic_load_n ((mem), __ATOMIC_ACQUIRE); }) + ({ __atomic_check_size_ls((mem)); \ + __atomic_load_n ((mem), __ATOMIC_ACQUIRE); }) # define atomic_store_relaxed(mem, val) \ do { \ - __atomic_check_size((mem)); \ + __atomic_check_size_ls((mem)); \ __atomic_store_n ((mem), (val), __ATOMIC_RELAXED); \ } while (0) # define atomic_store_release(mem, val) \ do { \ - __atomic_check_size((mem)); \ + __atomic_check_size_ls((mem)); \ __atomic_store_n ((mem), (val), __ATOMIC_RELEASE); \ } while (0) -- cgit v1.2.3