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authorMathieu Desnoyers <mathieu.desnoyers@efficios.com>2018-01-29 23:20:11 +0300
committerIngo Molnar <mingo@kernel.org>2018-02-05 23:34:02 +0300
commit3ccfebedd8cf54e291c809c838d8ad5cc00f5688 (patch)
tree1366b6cb9a9b7af1fa8f4eb8fc252f897eaf1ba8 /init
parent667ca1ec7c9eb7ac3b80590b6597151b4c2a750b (diff)
downloadlinux-3ccfebedd8cf54e291c809c838d8ad5cc00f5688.tar.xz
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/Kconfig3
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