On Thu, Mar 10, 2022 at 10:12:40PM +0100, Mark Kettenis wrote: > > Date: Thu, 10 Mar 2022 21:53:13 +0100 > > From: Alexander Bluhm <[email protected]> > > > > Hi, > > > > claudio@ mentioned that documentation for membar_enter_after_atomic > > and membar_exit_before_atomic is missing. > > > > ok? > > I think this is fine, although it doesn't actually define what an > "atomic operation" is in this context. Now we we only actually > provide an optimized implementation on x86; on all other architectures > that we support, these are just aliases for membar_enter() and > membar_exit(). So all x86 operations that perform a bus lock are > supported. However the atomic_load_xxx() and atomic_store_xxx() > operations you just introduced do not fall into this category.
I added a paragraph explaining where membar atomic can be used. > Not sure if that needs spelling out. And if it does, maybe the chosen > names for those functions are wrong? Names atomic_load/store are used in FreeBSD and NetBSD. Linux calls them atomic_read/set. Index: share/man/man9/membar_sync.9 =================================================================== RCS file: /data/mirror/openbsd/cvs/src/share/man/man9/membar_sync.9,v retrieving revision 1.3 diff -u -p -r1.3 membar_sync.9 --- share/man/man9/membar_sync.9 14 Feb 2014 05:11:55 -0000 1.3 +++ share/man/man9/membar_sync.9 13 Mar 2022 20:59:27 -0000 @@ -35,7 +35,9 @@ .Nm membar_exit , .Nm membar_producer , .Nm membar_consumer , -.Nm membar_sync +.Nm membar_sync , +.Nm membar_enter_after_atomic , +.Nm membar_exit_before_atomic .Nd memory access barrier operations .Sh SYNOPSIS .In sys/atomic.h @@ -49,6 +51,10 @@ .Fn membar_consumer "void" .Ft void .Fn membar_sync "void" +.Ft void +.Fn membar_enter_after_atomic "void" +.Ft void +.Fn membar_exit_before_atomic "void" .Sh DESCRIPTION The membar set of functions provide an interface for issuing memory barrier access operations with respect to multiple processors in the system. @@ -79,14 +85,38 @@ after the memory barrier complete. All loads and stores preceding the memory barrier will complete and reach global visibility before any loads and stores after the memory barrier complete and reach global visibility. +.It Fn membar_enter_after_atomic +An atomic operation preceding +.Fn membar_enter_after_atomic +will reach global visibility before all loads and stores following it. +The atomic operation is used to protect the start of a critical section. +.It Fn membar_exit_before_atomic +All loads and stores preceding +.Fn membar_exit_before_atomic +will reach global visibility before atomic operation that follows it. +The atomic operation is used to protect the end of a critical section. .El +.Pp +The atomic operations that can be used with +.Fn membar_enter_after_atomic +and +.Fn membar_exit_before_atomic +are the atomic_add, atomic_sub, atomic_inc, and atomic_dec set of +functions. +For other cases use +.Fn membar_enter +or +.Fn membar_exit . .Sh CONTEXT .Fn membar_enter , .Fn membar_exit , .Fn membar_producer , .Fn membar_consumer , -.Fn membar_sync -can all be called during autoconf, from process context, or from interrupt context. +.Fn membar_sync , +.Fn membar_enter_after_atomic , +.Fn membar_exit_before_atomic +can all be called during autoconf, from process context, or from +interrupt context. .Sh HISTORY The membar functions first appeared in .Nx 5.0
