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| author |   Mathieu Desnoyers <mathieu.desnoyers@efficios.com> | 2018-01-29 15:20:11 -0500 |
|---|---|---|
| committer |   Ingo Molnar <mingo@kernel.org> | 2018-02-05 21:34:02 +0100 |
| commit | 3ccfebedd8cf54e291c809c838d8ad5cc00f5688 (patch) | |
| tree | 1366b6cb9a9b7af1fa8f4eb8fc252f897eaf1ba8 /init | |
| parent | membarrier/selftest: Test private expedited command (diff) | |
| download | linux-dev-3ccfebedd8cf54e291c809c838d8ad5cc00f5688.tar.xz linux-dev-3ccfebedd8cf54e291c809c838d8ad5cc00f5688.zip | |
powerpc, membarrier: Skip memory barrier in switch_mm()
Allow PowerPC to skip the full memory barrier in switch_mm(), and
only issue the barrier when scheduling into a task belonging to a
process that has registered to use expedited private.
Threads targeting the same VM but which belong to different thread
groups is a tricky case. It has a few consequences:
It turns out that we cannot rely on get_nr_threads(p) to count the
number of threads using a VM. We can use
(atomic_read(&mm->mm_users) == 1 && get_nr_threads(p) == 1)
instead to skip the synchronize_sched() for cases where the VM only has
a single user, and that user only has a single thread.
It also turns out that we cannot use for_each_thread() to set
thread flags in all threads using a VM, as it only iterates on the
thread group.
Therefore, test the membarrier state variable directly rather than
relying on thread flags. This means
membarrier_register_private_expedited() needs to set the
MEMBARRIER_STATE_PRIVATE_EXPEDITED flag, issue synchronize_sched(), and
only then set MEMBARRIER_STATE_PRIVATE_EXPEDITED_READY which allows
private expedited membarrier commands to succeed.
membarrier_arch_switch_mm() now tests for the
MEMBARRIER_STATE_PRIVATE_EXPEDITED flag.
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: Alan Stern <stern@rowland.harvard.edu>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
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: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Maged Michael <maged.michael@gmail.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nicholas Piggin <npiggin@gmail.com>
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
Cc: linux-arch@vger.kernel.org
Cc: linuxppc-dev@lists.ozlabs.org
Link: http://lkml.kernel.org/r/20180129202020.8515-3-mathieu.desnoyers@efficios.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'init')
| -rw-r--r-- | init/Kconfig | 3 |
1 files changed, 3 insertions, 0 deletions
diff --git a/init/Kconfig b/init/Kconfig index a9a2e2c86671..837adcf075d9 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -1412,6 +1412,9 @@ config USERFAULTFD Enable the userfaultfd() system call that allows to intercept and handle page faults in userland. +config ARCH_HAS_MEMBARRIER_CALLBACKS + bool + config EMBEDDED bool "Embedded system" option allnoconfig_y |