Commit c6d68c1c authored Sep 19, 2019 by Mathieu Desnoyers Committed by Ingo Molnar Sep 25, 2019

sched/membarrier: Skip IPIs when mm->mm_users == 1

If there is only a single mm_user for the mm, the private expedited
membarrier command can skip the IPIs, because only a single thread
is using the mm.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Chris Metcalf <cmetcalf@ezchip.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Kirill Tkhai <tkhai@yandex.ru>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Paul E. McKenney <paulmck@linux.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Russell King - ARM Linux admin <linux@armlinux.org.uk>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20190919173705.2181-7-mathieu.desnoyers@efficios.com

Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 19a4ff53

kernel/sched/membarrier.c

+5 −4

Original line number	Diff line number	Diff line
		@@ -145,20 +145,21 @@ static int membarrier_private_expedited(int flags)
		int cpu;
		bool fallback = false;
		cpumask_var_t tmpmask;
		struct mm_struct *mm = current->mm;

		if (flags & MEMBARRIER_FLAG_SYNC_CORE) {
		if (!IS_ENABLED(CONFIG_ARCH_HAS_MEMBARRIER_SYNC_CORE))
		return -EINVAL;
		if (!(atomic_read(&current->mm->membarrier_state) &
		if (!(atomic_read(&mm->membarrier_state) &
		MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE_READY))
		return -EPERM;
		} else {
		if (!(atomic_read(&current->mm->membarrier_state) &
		if (!(atomic_read(&mm->membarrier_state) &
		MEMBARRIER_STATE_PRIVATE_EXPEDITED_READY))
		return -EPERM;
		}

		if (num_online_cpus() == 1)
		if (atomic_read(&mm->mm_users) == 1 \|\| num_online_cpus() == 1)
		return 0;

		/*
		@@ -194,7 +195,7 @@ static int membarrier_private_expedited(int flags)
		continue;
		rcu_read_lock();
		p = rcu_dereference(cpu_rq(cpu)->curr);
		if (p && p->mm == current->mm) {
		if (p && p->mm == mm) {
		if (!fallback)
		__cpumask_set_cpu(cpu, tmpmask);
		else

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