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Mathieu Desnoyers c5f58bd58f membarrier: Provide GLOBAL_EXPEDITED command 
Allow expedited membarrier to be used for data shared between processes
through shared memory.

Processes wishing to receive the membarriers register with
MEMBARRIER_CMD_REGISTER_GLOBAL_EXPEDITED. Those which want to issue
membarrier invoke MEMBARRIER_CMD_GLOBAL_EXPEDITED.

This allows extremely simple kernel-level implementation: we have almost
everything we need with the PRIVATE_EXPEDITED barrier code. All we need
to do is to add a flag in the mm_struct that will be used to check
whether we need to send the IPI to the current thread of each CPU.

There is a slight downside to this approach compared to targeting
specific shared memory users: when performing a membarrier operation,
all registered "global" receivers will get the barrier, even if they
don't share a memory mapping with the sender issuing
MEMBARRIER_CMD_GLOBAL_EXPEDITED.

This registration approach seems to fit the requirement of not
disturbing processes that really deeply care about real-time: they
simply should not register with MEMBARRIER_CMD_REGISTER_GLOBAL_EXPEDITED.

In order to align the membarrier command names, the "MEMBARRIER_CMD_SHARED"
command is renamed to "MEMBARRIER_CMD_GLOBAL", keeping an alias of
MEMBARRIER_CMD_SHARED to MEMBARRIER_CMD_GLOBAL for UAPI header backward
compatibility.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrea Parri <parri.andrea@gmail.com>
Cc: Andrew Hunter <ahh@google.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Avi Kivity <avi@scylladb.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Dave Watson <davejwatson@fb.com>
Cc: David Sehr <sehr@google.com>
Cc: Greg Hackmann <ghackmann@google.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Maged Michael <maged.michael@gmail.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Will Deacon <will.deacon@arm.com>
Cc: linux-api@vger.kernel.org
Link: http://lkml.kernel.org/r/20180129202020.8515-5-mathieu.desnoyers@efficios.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-02-05 21:34:31 +01:00
..
asm-generic bpf: correct broken uapi for BPF_PROG_TYPE_PERF_EVENT program type 2017-12-05 15:02:40 +01:00
drm main drm pull request for v4.15 2017-11-15 20:42:10 -08:00
linux membarrier: Provide GLOBAL_EXPEDITED command 2018-02-05 21:34:31 +01:00
misc License cleanup: add SPDX license identifier to uapi header files with a license 2017-11-02 11:20:11 +01:00
mtd License cleanup: add SPDX license identifier to uapi header files with a license 2017-11-02 11:20:11 +01:00
rdma Updates for 4.15 kernel merge window 2017-11-15 14:54:53 -08:00
scsi License cleanup: add SPDX license identifier to uapi header files with a license 2017-11-02 11:20:11 +01:00
sound Merge remote-tracking branches 'asoc/topic/fsl', 'asoc/topic/fsl-ssi', 'asoc/topic/fsl_asrc' and 'asoc/topic/hdac_hdmi' into asoc-next 2018-01-18 11:55:56 +00:00
video License cleanup: add SPDX license identifier to uapi header files with a license 2017-11-02 11:20:11 +01:00
xen License cleanup: add SPDX license identifier to uapi header files with a license 2017-11-02 11:20:11 +01:00