Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752140AbbEFQEs (ORCPT ); Wed, 6 May 2015 12:04:48 -0400 Received: from mail-wi0-f169.google.com ([209.85.212.169]:38072 "EHLO mail-wi0-f169.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751638AbbEFQEm (ORCPT ); Wed, 6 May 2015 12:04:42 -0400 From: Frederic Weisbecker To: Ingo Molnar Cc: LKML , Frederic Weisbecker , "Rafael J . Wysocki" , Peter Zijlstra , Mike Galbraith , Chris Metcalf , Dave Jones , Thomas Gleixner , Oleg Nesterov , "Paul E . McKenney" , Ingo Molnar , Rik van Riel , Martin Schwidefsky Subject: [PATCH 2/4] context_tracking: Inherit TIF_NOHZ through forks instead of context switches Date: Wed, 6 May 2015 18:04:24 +0200 Message-Id: <1430928266-24888-3-git-send-email-fweisbec@gmail.com> X-Mailer: git-send-email 2.1.4 In-Reply-To: <1430928266-24888-1-git-send-email-fweisbec@gmail.com> References: <1430928266-24888-1-git-send-email-fweisbec@gmail.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5619 Lines: 161 TIF_NOHZ is used by context_tracking to force syscall slow-path on every task in order to track userspace roundtrips. As such, it must be set on all running tasks. It's currently explicitly inherited through context switches. There is no need to do it on this fast-path though. The flag could be simply set once for all on all tasks, whether they are running or not. Lets do this by setting the flag to init task on early boot and let it propagate through fork inheritance. While at it mark context_tracking_cpu_set() as init code, we only need it at early boot time. Suggested-by: Oleg Nesterov Reviewed-by: Rik van Riel Signed-off-by: Frederic Weisbecker Cc: Thomas Gleixner Cc: Peter Zijlstra Cc: Rik van Riel Cc: Paul E. McKenney Cc: Ingo Molnar Cc: Dave Jones Cc: Oleg Nesterov --- include/linux/context_tracking.h | 10 --------- include/linux/sched.h | 3 +++ kernel/context_tracking.c | 44 +++++++++++++++++----------------------- kernel/sched/core.c | 1 - 4 files changed, 22 insertions(+), 36 deletions(-) diff --git a/include/linux/context_tracking.h b/include/linux/context_tracking.h index 2821838..b96bd29 100644 --- a/include/linux/context_tracking.h +++ b/include/linux/context_tracking.h @@ -14,8 +14,6 @@ extern void context_tracking_enter(enum ctx_state state); extern void context_tracking_exit(enum ctx_state state); extern void context_tracking_user_enter(void); extern void context_tracking_user_exit(void); -extern void __context_tracking_task_switch(struct task_struct *prev, - struct task_struct *next); static inline void user_enter(void) { @@ -51,19 +49,11 @@ static inline void exception_exit(enum ctx_state prev_ctx) } } -static inline void context_tracking_task_switch(struct task_struct *prev, - struct task_struct *next) -{ - if (context_tracking_is_enabled()) - __context_tracking_task_switch(prev, next); -} #else static inline void user_enter(void) { } static inline void user_exit(void) { } static inline enum ctx_state exception_enter(void) { return 0; } static inline void exception_exit(enum ctx_state prev_ctx) { } -static inline void context_tracking_task_switch(struct task_struct *prev, - struct task_struct *next) { } #endif /* !CONFIG_CONTEXT_TRACKING */ diff --git a/include/linux/sched.h b/include/linux/sched.h index 8222ae4..f5d4f9e 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -2540,6 +2540,9 @@ static inline unsigned long wait_task_inactive(struct task_struct *p, } #endif +#define tasklist_empty() \ + list_empty(&init_task.tasks) + #define next_task(p) \ list_entry_rcu((p)->tasks.next, struct task_struct, tasks) diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c index b9e0b4f..a3aaca7 100644 --- a/kernel/context_tracking.c +++ b/kernel/context_tracking.c @@ -30,14 +30,6 @@ EXPORT_SYMBOL_GPL(context_tracking_enabled); DEFINE_PER_CPU(struct context_tracking, context_tracking); EXPORT_SYMBOL_GPL(context_tracking); -void context_tracking_cpu_set(int cpu) -{ - if (!per_cpu(context_tracking.active, cpu)) { - per_cpu(context_tracking.active, cpu) = true; - static_key_slow_inc(&context_tracking_enabled); - } -} - static bool context_tracking_recursion_enter(void) { int recursion; @@ -194,24 +186,26 @@ void context_tracking_user_exit(void) } NOKPROBE_SYMBOL(context_tracking_user_exit); -/** - * __context_tracking_task_switch - context switch the syscall callbacks - * @prev: the task that is being switched out - * @next: the task that is being switched in - * - * The context tracking uses the syscall slow path to implement its user-kernel - * boundaries probes on syscalls. This way it doesn't impact the syscall fast - * path on CPUs that don't do context tracking. - * - * But we need to clear the flag on the previous task because it may later - * migrate to some CPU that doesn't do the context tracking. As such the TIF - * flag may not be desired there. - */ -void __context_tracking_task_switch(struct task_struct *prev, - struct task_struct *next) +void __init context_tracking_cpu_set(int cpu) { - clear_tsk_thread_flag(prev, TIF_NOHZ); - set_tsk_thread_flag(next, TIF_NOHZ); + static __initdata bool initialized = false; + + if (!per_cpu(context_tracking.active, cpu)) { + per_cpu(context_tracking.active, cpu) = true; + static_key_slow_inc(&context_tracking_enabled); + } + + if (initialized) + return; + + /* + * Set TIF_NOHZ to init/0 and let it propagate to all tasks through fork + * This assumes that init is the only task at this early boot stage. + */ + set_tsk_thread_flag(&init_task, TIF_NOHZ); + WARN_ON_ONCE(!tasklist_empty()); + + initialized = true; } #ifdef CONFIG_CONTEXT_TRACKING_FORCE diff --git a/kernel/sched/core.c b/kernel/sched/core.c index d8a6196..6f149f8 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -2338,7 +2338,6 @@ context_switch(struct rq *rq, struct task_struct *prev, */ spin_release(&rq->lock.dep_map, 1, _THIS_IP_); - context_tracking_task_switch(prev, next); /* Here we just switch the register state and the stack. */ switch_to(prev, next, prev); barrier(); -- 2.1.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/