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SubjectRe: [RFC PATCH 3/3] Update membarrier manpage for 4.14, 4.15
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Hi Mathieu,

On 11/16/2017 04:17 PM, Mathieu Desnoyers wrote:
> Add documentation for those new membarrier commands:
>
> New in 4.14:
> MEMBARRIER_CMD_PRIVATE_EXPEDITED
> MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED
>
> Adapt the MEMBARRIER_CMD_SHARED return value documentation to reflect
> that it now returns -EINVAL when issued on a system configured for
> nohz_full.
>
> New in 4.15:
> MEMBARRIER_CMD_SHARED_EXPEDITED
> MEMBARRIER_CMD_REGISTER_SHARED_EXPEDITED

Combining details into one patch in this way makes things more difficult
for me. I would prefer these details to be split into separate pieces
for the 4.14 and 4.15 changes, in part because of the way the man-pages
release cycle currently works (roughly synchronized with kernel releases)
and also because the 4.15 details might change.

I've applied the 4.14 details from this patch to the man page; if you had a
chance to check whether I did that job correctly, that would be great.
See the patch below.

Once the pieces get merged for 4.15, could you ping me/resend a patch for
the 4.15 changes please.

Cheers,

Michael


diff --git a/man2/membarrier.2 b/man2/membarrier.2
index bbf611e10..6390f9693 100644
--- a/man2/membarrier.2
+++ b/man2/membarrier.2
@@ -1,4 +1,4 @@
-.\" Copyright 2015 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
+.\" Copyright 2015-2017 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
.\"
.\" %%%LICENSE_START(VERBATIM)
.\" Permission is granted to make and distribute verbatim copies of this
@@ -22,7 +22,7 @@
.\" the source, must acknowledge the copyright and authors of this work.
.\" %%%LICENSE_END
.\"
-.TH MEMBARRIER 2 2017-09-15 "Linux" "Linux Programmer's Manual"
+.TH MEMBARRIER 2 2017-11-15 "Linux" "Linux Programmer's Manual"
.SH NAME
membarrier \- issue memory barriers on a set of threads
.SH SYNOPSIS
@@ -87,6 +87,25 @@ order between entry to and return from the
.BR membarrier ()
system call.
All threads on the system are targeted by this command.
+.TP
+.BR MEMBARRIER_CMD_PRIVATE_EXPEDITED " (since Linux 4.14)"
+Execute a memory barrier on each running thread belonging to the same
+process as the current thread.
+Upon return from system call, the calling
+thread is assured that all its running threads siblings have passed
+through a state where all memory accesses to user-space addresses match
+program order between entry to and return from the system call
+(non-running threads are de facto in such a state).
+This covers only threads from the same process as the calling thread.
+.IP
+The "expedited" commands complete faster than the non-expedited ones;
+they never block, but have the downside of causing extra overhead.
+A process needs to register its intent to use the private
+expedited command prior to using it.
+.TP
+.BR MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED " (since Linux 4.14)"
+Register the process's intent to use
+.BR MEMBARRIER_CMD_PRIVATE_EXPEDITED .
.PP
The
.I flags
@@ -117,9 +136,12 @@ The pair ordering is detailed as (O: ordered, X: not ordered):
.SH RETURN VALUE
On success, the
.B MEMBARRIER_CMD_QUERY
-operation returns a bit mask of supported commands and the
-.B MEMBARRIER_CMD_SHARED
-operation returns zero.
+operation returns a bit mask of supported commands, and the
+.B MEMBARRIER_CMD_SHARED ,
+.B MEMBARRIER_CMD_PRIVATE_EXPEDITED ,
+and
+.B MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED ,
+operations return zero.
On error, \-1 is returned,
and
.I errno
@@ -138,22 +160,22 @@ set to 0, error handling is required only for the first call to
.TP
.B EINVAL
.I cmd
-is invalid or
+is invalid, or
.I flags
-is non-zero.
+is non-zero, or the
+.BR MEMBARRIER_CMD_SHARED
+command is disabled because the
+.I nohz_full
+CPU parameter has been set.
.TP
.B ENOSYS
The
.BR membarrier ()
system call is not implemented by this kernel.
.TP
-.BR ENOSYS " (since Linux 4.11)"
-.\" 907565337ebf998a68cb5c5b2174ce5e5da065eb
-The
-.BR membarrier ()
-system call is disabled because the
-.I nohz_full
-CPU parameter has been set.
+.B EPERM
+The current process was not registered prior to using private expedited
+commands.
.SH VERSIONS
The
.BR membarrier ()
@@ -162,6 +184,10 @@ system call was added in Linux 4.3.
.SH CONFORMING TO
.BR membarrier ()
is Linux-specific.
+.\" .SH SEE ALSO
+.\" FIXME See if the following syscalls make it into Linux 4.15 or later
+.\" .BR cpu_opv (2),
+.\" .BR rseq (2)
.SH NOTES
A memory barrier instruction is part of the instruction set of
architectures with weakly-ordered memory models.
--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/

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