]> git.proxmox.com Git - mirror_ubuntu-kernels.git/commit
membarrier: Provide register expedited private command
authorMathieu Desnoyers <mathieu.desnoyers@efficios.com>
Thu, 19 Oct 2017 17:30:15 +0000 (13:30 -0400)
committerLinus Torvalds <torvalds@linux-foundation.org>
Fri, 20 Oct 2017 02:13:40 +0000 (22:13 -0400)
commita961e40917fb14614d368d8bc9782ca4d6a8cd11
treebb2778144007d317d197b4f6cb5816ae91afb300
parent96f893abc87bd29339c973edf6068a064cb8a756
membarrier: Provide register expedited private command

This introduces a "register private expedited" membarrier command which
allows eventual removal of important memory barrier constraints on the
scheduler fast-paths. It changes how the "private expedited" membarrier
command (new to 4.14) is used from user-space.

This new command allows processes to register their intent to use the
private expedited command.  This affects how the expedited private
command introduced in 4.14-rc is meant to be used, and should be merged
before 4.14 final.

Processes are now required to register before using
MEMBARRIER_CMD_PRIVATE_EXPEDITED, otherwise that command returns EPERM.

This fixes a problem that arose when designing requested extensions to
sys_membarrier() to allow JITs to efficiently flush old code from
instruction caches.  Several potential algorithms are much less painful
if the user register intent to use this functionality early on, for
example, before the process spawns the second thread.  Registering at
this time removes the need to interrupt each and every thread in that
process at the first expedited sys_membarrier() system call.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
fs/exec.c
include/linux/mm_types.h
include/linux/sched/mm.h
include/uapi/linux/membarrier.h
kernel/sched/membarrier.c