From c6d68c1c4a4d6611fc0f8145d764226571d737ca Mon Sep 17 00:00:00 2001 From: Mathieu Desnoyers Date: Thu, 19 Sep 2019 13:37:04 -0400 Subject: [PATCH] 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 Signed-off-by: Peter Zijlstra (Intel) Cc: Chris Metcalf Cc: Christoph Lameter Cc: Eric W. Biederman Cc: Kirill Tkhai Cc: Linus Torvalds Cc: Mike Galbraith Cc: Oleg Nesterov Cc: Paul E. McKenney Cc: Peter Zijlstra Cc: Russell King - ARM Linux admin Cc: Thomas Gleixner Link: https://lkml.kernel.org/r/20190919173705.2181-7-mathieu.desnoyers@efficios.com Signed-off-by: Ingo Molnar --- kernel/sched/membarrier.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-) diff --git a/kernel/sched/membarrier.c b/kernel/sched/membarrier.c index 070cf433bb9a..fced54ad0f3d 100644 --- a/kernel/sched/membarrier.c +++ b/kernel/sched/membarrier.c @@ -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(¤t->mm->membarrier_state) & + if (!(atomic_read(&mm->membarrier_state) & MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE_READY)) return -EPERM; } else { - if (!(atomic_read(¤t->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