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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>
82 lines
4.1 KiB
C
82 lines
4.1 KiB
C
#ifndef _UAPI_LINUX_MEMBARRIER_H
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#define _UAPI_LINUX_MEMBARRIER_H
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/*
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* linux/membarrier.h
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*
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* membarrier system call API
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*
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* Copyright (c) 2010, 2015 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
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* in the Software without restriction, including without limitation the rights
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* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in
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* all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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* SOFTWARE.
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*/
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/**
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* enum membarrier_cmd - membarrier system call command
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* @MEMBARRIER_CMD_QUERY: Query the set of supported commands. It returns
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* a bitmask of valid commands.
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* @MEMBARRIER_CMD_SHARED: Execute a memory barrier on all running threads.
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* Upon return from system call, the caller thread
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* is ensured that all running threads have passed
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* through a state where all memory accesses to
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* user-space addresses match program order between
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* entry to and return from the system call
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* (non-running threads are de facto in such a
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* state). This covers threads from all processes
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* running on the system. This command returns 0.
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* @MEMBARRIER_CMD_PRIVATE_EXPEDITED:
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* Execute a memory barrier on each running
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* thread belonging to the same process as the current
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* thread. Upon return from system call, the
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* caller thread is ensured that all its running
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* threads siblings have passed through a state
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* where all memory accesses to user-space
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* addresses match program order between entry
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* to and return from the system call
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* (non-running threads are de facto in such a
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* state). This only covers threads from the
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* same processes as the caller thread. This
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* command returns 0 on success. The
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* "expedited" commands complete faster than
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* the non-expedited ones, they never block,
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* but have the downside of causing extra
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* overhead. A process needs to register its
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* intent to use the private expedited command
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* prior to using it, otherwise this command
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* returns -EPERM.
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* @MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED:
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* Register the process intent to use
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* MEMBARRIER_CMD_PRIVATE_EXPEDITED. Always
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* returns 0.
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*
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* Command to be passed to the membarrier system call. The commands need to
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* be a single bit each, except for MEMBARRIER_CMD_QUERY which is assigned to
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* the value 0.
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*/
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enum membarrier_cmd {
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MEMBARRIER_CMD_QUERY = 0,
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MEMBARRIER_CMD_SHARED = (1 << 0),
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/* reserved for MEMBARRIER_CMD_SHARED_EXPEDITED (1 << 1) */
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/* reserved for MEMBARRIER_CMD_PRIVATE (1 << 2) */
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MEMBARRIER_CMD_PRIVATE_EXPEDITED = (1 << 3),
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MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED = (1 << 4),
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};
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#endif /* _UAPI_LINUX_MEMBARRIER_H */
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