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membarrier: Provide GLOBAL_EXPEDITED command

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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>
This commit is contained in:
Mathieu Desnoyers 2018-01-29 15:20:13 -05:00 • committed by Ingo Molnar
parent 306e060435
commit c5f58bd58f
4 changed files with 153 additions and 18 deletions
Download patch file Download diff file Expand all files Collapse all files

42
include/uapi/linux/membarrier.h
View file

@ -31,7 +31,7 @@
* enum membarrier_cmd - membarrier system call command
* @MEMBARRIER_CMD_QUERY: Query the set of supported commands. It returns
* a bitmask of valid commands.
* @MEMBARRIER_CMD_SHARED: Execute a memory barrier on all running threads.
* @MEMBARRIER_CMD_GLOBAL: Execute a memory barrier on all running threads.
* Upon return from system call, the caller thread
* is ensured that all running threads have passed
* through a state where all memory accesses to
@ -40,6 +40,28 @@
* (non-running threads are de facto in such a
* state). This covers threads from all processes
* running on the system. This command returns 0.
* @MEMBARRIER_CMD_GLOBAL_EXPEDITED:
* Execute a memory barrier on all running threads
* of all processes which previously registered
* with MEMBARRIER_CMD_REGISTER_GLOBAL_EXPEDITED.
* Upon return from system call, the caller thread
* is ensured that all running threads 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 only covers threads from processes
* which registered with
* MEMBARRIER_CMD_REGISTER_GLOBAL_EXPEDITED.
* This command returns 0. Given that
* registration is about the intent to receive
* the barriers, it is valid to invoke
* MEMBARRIER_CMD_GLOBAL_EXPEDITED from a
* non-registered process.
* @MEMBARRIER_CMD_REGISTER_GLOBAL_EXPEDITED:
* Register the process intent to receive
* MEMBARRIER_CMD_GLOBAL_EXPEDITED memory
* barriers. Always returns 0.
* @MEMBARRIER_CMD_PRIVATE_EXPEDITED:
* Execute a memory barrier on each running
* thread belonging to the same process as the current
@ -64,18 +86,24 @@
* Register the process intent to use
* MEMBARRIER_CMD_PRIVATE_EXPEDITED. Always
* returns 0.
* @MEMBARRIER_CMD_SHARED:
* Alias to MEMBARRIER_CMD_GLOBAL. Provided for
* header backward compatibility.
*
* Command to be passed to the membarrier system call. The commands need to
* be a single bit each, except for MEMBARRIER_CMD_QUERY which is assigned to
* the value 0.
*/
enum membarrier_cmd {
MEMBARRIER_CMD_QUERY = 0,
MEMBARRIER_CMD_SHARED = (1 << 0),
/* reserved for MEMBARRIER_CMD_SHARED_EXPEDITED (1 << 1) */
/* reserved for MEMBARRIER_CMD_PRIVATE (1 << 2) */
MEMBARRIER_CMD_PRIVATE_EXPEDITED = (1 << 3),
MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED = (1 << 4),
MEMBARRIER_CMD_QUERY = 0,
MEMBARRIER_CMD_GLOBAL = (1 << 0),
MEMBARRIER_CMD_GLOBAL_EXPEDITED = (1 << 1),
MEMBARRIER_CMD_REGISTER_GLOBAL_EXPEDITED = (1 << 2),
MEMBARRIER_CMD_PRIVATE_EXPEDITED = (1 << 3),
MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED = (1 << 4),
/* Alias for header backward compatibility. */
MEMBARRIER_CMD_SHARED = MEMBARRIER_CMD_GLOBAL,
};
#endif /* _UAPI_LINUX_MEMBARRIER_H */