From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS, USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2C32DC43142 for ; Mon, 30 Jul 2018 22:24:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C5C6820857 for ; Mon, 30 Jul 2018 22:24:51 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=joelfernandes.org header.i=@joelfernandes.org header.b="E/adBkTl" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C5C6820857 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=joelfernandes.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731994AbeGaABy (ORCPT ); Mon, 30 Jul 2018 20:01:54 -0400 Received: from mail-pg1-f196.google.com ([209.85.215.196]:43932 "EHLO mail-pg1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726622AbeGaABx (ORCPT ); Mon, 30 Jul 2018 20:01:53 -0400 Received: by mail-pg1-f196.google.com with SMTP id d17-v6so3551277pgv.10 for ; Mon, 30 Jul 2018 15:24:48 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=joelfernandes.org; s=google; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=hsnFwcN7mJfKlH6J0vgYGpAWbL9lQblexuCLGnoVpEo=; b=E/adBkTl/P1KqJXNmX2N6sZR3baBZCKuEyzVhWwJ/GEmHZJihOSnpti7Qe4MQ3gHrd ODUFGb0gM1jK9bJ+4HigGbCKnCu75PxGLuNMGtO8XLJs92Gd8n4Z3zzKy/msBXzJUjeC ALRuJwPahGyVcjql+4dwFy0F9fecN7HOdl14k= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=hsnFwcN7mJfKlH6J0vgYGpAWbL9lQblexuCLGnoVpEo=; b=IiryTU2KXLGCEjZ07kqi6iLclzx86+AeZAK0WzE+ZqC2bEx7Z5MrPkN/Qdojubowe1 uWdpQvYhoX3HHPKQ1u2YoYe042KpkbWty9zN75soeUDK4PMZTwWmPmxFDnHvEsOMVT0v usZo+TPqiPkYjmZ1FSIUZaIymxVBXVLe+YWmM/vy3k9efVQCdWVrHlnQdj5YTLBvv29k gv1x01sQBaGghC2+e6QTlnyF1evobZhW4khNrgbqKd9gGniTIVJ+VLHH2LVbc4IY4c2V bQ+BXBnjtoYu2DyhAKAwd58z39acU1PMKBJvUYbfdkI+C7Ykb5ZTtrBBDPJNgI58Zxc3 7pCQ== X-Gm-Message-State: AOUpUlG+E92Sd5BNToDaIntwqD1m9W70IORBetmMGgD3Lzhej5o8iaGs Od/mX/5cGUbiEwchUobY/VmIE1qItGk= X-Google-Smtp-Source: AAOMgpd+4G0/qxXVe7jRExIs3S175iu9gI0SVJqw5GJsrYEmY861s9Y9WKUaiI5L4KwXTnN+yqRpHw== X-Received: by 2002:a62:d693:: with SMTP id a19-v6mr19396488pfl.248.1532989487593; Mon, 30 Jul 2018 15:24:47 -0700 (PDT) Received: from joelaf.mtv.corp.google.com ([2620:0:1000:1600:3122:ea9c:d178:eb]) by smtp.gmail.com with ESMTPSA id t21-v6sm21183914pfi.73.2018.07.30.15.24.46 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 30 Jul 2018 15:24:47 -0700 (PDT) From: Joel Fernandes To: linux-kernel@vger.kernel.org Cc: kernel-team@android.com, "Joel Fernandes (Google)" , Boqun Feng , Byungchul Park , Ingo Molnar , Masami Hiramatsu , Mathieu Desnoyers , Namhyung Kim , Paul McKenney , Peter Zijlstra , Steven Rostedt , Thomas Glexiner , Tom Zanussi Subject: [PATCH v12 2/3] tracepoint: Make rcuidle tracepoint callers use SRCU Date: Mon, 30 Jul 2018 15:24:22 -0700 Message-Id: <20180730222423.196630-3-joel@joelfernandes.org> X-Mailer: git-send-email 2.18.0.345.g5c9ce644c3-goog In-Reply-To: <20180730222423.196630-1-joel@joelfernandes.org> References: <20180730222423.196630-1-joel@joelfernandes.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: "Joel Fernandes (Google)" 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. Test: Tested idle and preempt/irq tracepoints. Here are some performance numbers: With a run of the following 30 times on a single core x86 Qemu instance with 1GB memory: hackbench -g 4 -f 2 -l 3000 Completion times in seconds. CONFIG_PROVE_LOCKING=y. No patches (without this series) Mean: 3.048 Median: 3.025 Std Dev: 0.064 With Lockdep using irq tracepoints with RCU implementation: Mean: 3.451 (-11.66 %) Median: 3.447 (-12.22%) Std Dev: 0.049 With Lockdep using irq tracepoints with SRCU implementation (this series): Mean: 3.020 (I would consider the improvement against the "without this series" case as just noise). Median: 3.013 Std Dev: 0.033 [1] https://patchwork.kernel.org/patch/10344297/ [remove rcu_read_lock_sched_notrace as its the equivalent of preempt_disable_notrace and is unnecessary to call in tracepoint code] Cleaned-up-by: Peter Zijlstra Acked-by: Peter Zijlstra Reviewed-by: Mathieu Desnoyers Signed-off-by: Joel Fernandes (Google) --- include/linux/tracepoint.h | 41 ++++++++++++++++++++++++++++++-------- kernel/tracepoint.c | 16 ++++++++++++++- 2 files changed, 48 insertions(+), 9 deletions(-) diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h index 19a690b559ca..6e7bc6ebfcd8 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 @@ -75,10 +78,16 @@ int unregister_tracepoint_module_notifier(struct notifier_block *nb) * probe unregistration and the end of module exit to make sure there is no * caller executing a probe when it is freed. */ +#ifdef CONFIG_TRACEPOINTS static inline void tracepoint_synchronize_unregister(void) { + synchronize_srcu(&tracepoint_srcu); synchronize_sched(); } +#else +static inline void tracepoint_synchronize_unregister(void) +{ } +#endif #ifdef CONFIG_HAVE_SYSCALL_TRACEPOINTS extern int syscall_regfunc(void); @@ -129,18 +138,32 @@ 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, rcuidle) \ 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); \ + \ + /* srcu can't be used from NMI */ \ + if (rcuidle && in_nmi()) \ + WARN_ON_ONCE(1); \ + \ + /* keep srcu and sched-rcu usage consistent */ \ + preempt_disable_notrace(); \ + \ + /* \ + * For rcuidle callers, use srcu since sched-rcu \ + * doesn't work from the idle path. \ + */ \ + if (rcuidle) \ + idx = srcu_read_lock_notrace(&tracepoint_srcu); \ + \ + it_func_ptr = rcu_dereference_raw((tp)->funcs); \ + \ if (it_func_ptr) { \ do { \ it_func = (it_func_ptr)->func; \ @@ -148,9 +171,11 @@ 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 (rcuidle) \ + srcu_read_unlock_notrace(&tracepoint_srcu, idx);\ + \ + preempt_enable_notrace(); \ } while (0) #ifndef MODULE diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c index 6dc6356c3327..955148d91b74 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; @@ -67,16 +70,27 @@ 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) { struct tp_probes *tp_probes = container_of(old, struct tp_probes, probes[0]); + /* + * Tracepoint probes are protected by both sched RCU and SRCU, + * by calling the SRCU callback in the sched RCU callback we + * cover both cases. So let us chain the SRCU and sched RCU + * callbacks to wait for both grace periods. + */ call_rcu_sched(&tp_probes->rcu, rcu_free_old_probes); } } -- 2.18.0.345.g5c9ce644c3-goog