From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751977AbeD0E1R (ORCPT ); Fri, 27 Apr 2018 00:27:17 -0400 Received: from mail-pf0-f193.google.com ([209.85.192.193]:36210 "EHLO mail-pf0-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750877AbeD0E1P (ORCPT ); Fri, 27 Apr 2018 00:27:15 -0400 X-Google-Smtp-Source: AB8JxZoo74zIdmh7fVwO9sM05KENYZlt2sJFJ529DsF8AahhS4gtPi7n/EqShniD05Qp7giL1P3lqg== From: Joel Fernandes To: linux-kernel@vger.kernel.org Cc: Joel Fernandes , Steven Rostedt , Peter Zilstra , Ingo Molnar , Mathieu Desnoyers , Tom Zanussi , Namhyung Kim , Thomas Glexiner , Boqun Feng , Paul McKenney , Frederic Weisbecker , Randy Dunlap , Masami Hiramatsu , Fenguang Wu , Baohong Liu , Vedang Patel , kernel-team@android.com Subject: [PATCH RFC] tracepoint: Introduce tracepoint callbacks executing with preempt on Date: Thu, 26 Apr 2018 21:26:56 -0700 Message-Id: <20180427042656.190746-1-joelaf@google.com> X-Mailer: git-send-email 2.17.0.441.gb46fe60e1d-goog Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org In recent tests with IRQ on/off tracepoints, a large performance overhead ~10% is noticed when running hackbench. This is root caused to calls to rcu_irq_enter_irqson and rcu_irq_exit_irqson from the tracepoint code. Following a long discussion on the list [1] about this, we concluded that srcu is a better alternative for use during rcu idle. Although it does involve extra barriers, its lighter than the sched-rcu version which has to do additional RCU calls to notify RCU idle about entry into RCU sections. In this patch, we change the underlying implementation of the trace_*_rcuidle API to use SRCU. This has shown to improve performance alot for the high frequency irq enable/disable tracepoints. In the future, we can add a new may_sleep API which can use this infrastructure for callbacks that actually can sleep which will support Mathieu's usecase of blocking probes. Test: Tested idle and preempt/irq tracepoints. [1] https://patchwork.kernel.org/patch/10344297/ Cc: Steven Rostedt Cc: Peter Zilstra Cc: Ingo Molnar Cc: Mathieu Desnoyers Cc: Tom Zanussi Cc: Namhyung Kim Cc: Thomas Glexiner Cc: Boqun Feng Cc: Paul McKenney Cc: Frederic Weisbecker Cc: Randy Dunlap Cc: Masami Hiramatsu Cc: Fenguang Wu Cc: Baohong Liu Cc: Vedang Patel Cc: kernel-team@android.com Signed-off-by: Joel Fernandes --- include/linux/tracepoint.h | 37 +++++++++++++++++++++++++++++-------- kernel/tracepoint.c | 10 +++++++++- 2 files changed, 38 insertions(+), 9 deletions(-) diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h index c94f466d57ef..a1c1987de423 100644 --- a/include/linux/tracepoint.h +++ b/include/linux/tracepoint.h @@ -15,6 +15,7 @@ */ #include +#include #include #include #include @@ -33,6 +34,8 @@ struct trace_eval_map { #define TRACEPOINT_DEFAULT_PRIO 10 +extern struct srcu_struct tracepoint_srcu; + extern int tracepoint_probe_register(struct tracepoint *tp, void *probe, void *data); extern int @@ -77,6 +80,7 @@ int unregister_tracepoint_module_notifier(struct notifier_block *nb) */ static inline void tracepoint_synchronize_unregister(void) { + synchronize_srcu(&tracepoint_srcu); synchronize_sched(); } @@ -129,18 +133,26 @@ extern void syscall_unregfunc(void); * as "(void *, void)". The DECLARE_TRACE_NOARGS() will pass in just * "void *data", where as the DECLARE_TRACE() will pass in "void *data, proto". */ -#define __DO_TRACE(tp, proto, args, cond, rcucheck) \ +#define __DO_TRACE(tp, proto, args, cond, preempt_on) \ do { \ struct tracepoint_func *it_func_ptr; \ void *it_func; \ void *__data; \ + int __maybe_unused idx = 0; \ \ if (!(cond)) \ return; \ - if (rcucheck) \ - rcu_irq_enter_irqson(); \ - rcu_read_lock_sched_notrace(); \ - it_func_ptr = rcu_dereference_sched((tp)->funcs); \ + if (preempt_on) { \ + WARN_ON_ONCE(in_nmi()); /* no srcu from nmi */ \ + idx = srcu_read_lock(&tracepoint_srcu); \ + it_func_ptr = srcu_dereference((tp)->funcs, \ + &tracepoint_srcu); \ + } else { \ + rcu_read_lock_sched_notrace(); \ + it_func_ptr = \ + rcu_dereference_sched((tp)->funcs); \ + } \ + \ if (it_func_ptr) { \ do { \ it_func = (it_func_ptr)->func; \ @@ -148,12 +160,21 @@ extern void syscall_unregfunc(void); ((void(*)(proto))(it_func))(args); \ } while ((++it_func_ptr)->func); \ } \ - rcu_read_unlock_sched_notrace(); \ - if (rcucheck) \ - rcu_irq_exit_irqson(); \ + \ + if (preempt_on) \ + srcu_read_unlock(&tracepoint_srcu, idx); \ + else \ + rcu_read_unlock_sched_notrace(); \ } while (0) #ifndef MODULE +/* + * This is for tracepoints that may be called from an rcu idle path. To make + * sure we its safe in the idle path, use the srcu instead of sched-rcu by + * specifying the preempt_on flag below. This has the obvious effect that any + * callback expecting preemption to be disabled should explicitly do so since + * with srcu it'd run with preempt on. + */ #define __DECLARE_TRACE_RCU(name, proto, args, cond, data_proto, data_args) \ static inline void trace_##name##_rcuidle(proto) \ { \ diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c index 671b13457387..b3b1d65a2460 100644 --- a/kernel/tracepoint.c +++ b/kernel/tracepoint.c @@ -31,6 +31,9 @@ extern struct tracepoint * const __start___tracepoints_ptrs[]; extern struct tracepoint * const __stop___tracepoints_ptrs[]; +DEFINE_SRCU(tracepoint_srcu); +EXPORT_SYMBOL_GPL(tracepoint_srcu); + /* Set to 1 to enable tracepoint debug output */ static const int tracepoint_debug; @@ -67,11 +70,16 @@ static inline void *allocate_probes(int count) return p == NULL ? NULL : p->probes; } -static void rcu_free_old_probes(struct rcu_head *head) +static void srcu_free_old_probes(struct rcu_head *head) { kfree(container_of(head, struct tp_probes, rcu)); } +static void rcu_free_old_probes(struct rcu_head *head) +{ + call_srcu(&tracepoint_srcu, head, srcu_free_old_probes); +} + static inline void release_probes(struct tracepoint_func *old) { if (old) { -- 2.17.0.441.gb46fe60e1d-goog