Date: Mon, 29 Jun 2015 09:58:40 +0000 (UTC) From: Konstantin Belousov <kib@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r284922 - in head/sys: amd64/include i386/include Message-ID: <201506290958.t5T9weY9024691@svn.freebsd.org>
next in thread | raw e-mail | index | archive | help
Author: kib Date: Mon Jun 29 09:58:40 2015 New Revision: 284922 URL: https://svnweb.freebsd.org/changeset/base/284922 Log: Add a comment about too strong semantic of atomic_load_acq() on x86. Submitted by: bde MFC after: 2 weeks Modified: head/sys/amd64/include/atomic.h head/sys/i386/include/atomic.h Modified: head/sys/amd64/include/atomic.h ============================================================================== --- head/sys/amd64/include/atomic.h Mon Jun 29 07:53:44 2015 (r284921) +++ head/sys/amd64/include/atomic.h Mon Jun 29 09:58:40 2015 (r284922) @@ -296,6 +296,15 @@ __storeload_barrier(void) } #endif /* _KERNEL*/ +/* + * C11-standard acq/rel semantics only apply when the variable in the + * call is the same for acq as it is for rel. However, our previous + * (x86) implementations provided much stronger ordering than required + * (essentially what is called seq_cst order in C11). This + * implementation provides the historical strong ordering since some + * callers depend on it. + */ + #define ATOMIC_LOAD(TYPE) \ static __inline u_##TYPE \ atomic_load_acq_##TYPE(volatile u_##TYPE *p) \ Modified: head/sys/i386/include/atomic.h ============================================================================== --- head/sys/i386/include/atomic.h Mon Jun 29 07:53:44 2015 (r284921) +++ head/sys/i386/include/atomic.h Mon Jun 29 09:58:40 2015 (r284922) @@ -278,6 +278,15 @@ __storeload_barrier(void) } #endif /* _KERNEL*/ +/* + * C11-standard acq/rel semantics only apply when the variable in the + * call is the same for acq as it is for rel. However, our previous + * (x86) implementations provided much stronger ordering than required + * (essentially what is called seq_cst order in C11). This + * implementation provides the historical strong ordering since some + * callers depend on it. + */ + #define ATOMIC_LOAD(TYPE) \ static __inline u_##TYPE \ atomic_load_acq_##TYPE(volatile u_##TYPE *p) \
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?201506290958.t5T9weY9024691>