From patchwork Thu Sep 10 20:20:50 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Paul E. McKenney" X-Patchwork-Id: 1361983 X-Patchwork-Delegate: davem@davemloft.net Return-Path: X-Original-To: incoming-bpf@patchwork.ozlabs.org Delivered-To: patchwork-incoming-bpf@bilbo.ozlabs.org Authentication-Results: ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=vger.kernel.org (client-ip=23.128.96.18; helo=vger.kernel.org; envelope-from=bpf-owner@vger.kernel.org; receiver=) Authentication-Results: ozlabs.org; dmarc=pass (p=none dis=none) header.from=kernel.org Authentication-Results: ozlabs.org; dkim=pass (1024-bit key; unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=default header.b=dgAf6k13; dkim-atps=neutral Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by ozlabs.org (Postfix) with ESMTP id 4BnWHg1X57z9sVS for ; Fri, 11 Sep 2020 06:50:39 +1000 (AEST) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726385AbgIJUue (ORCPT ); Thu, 10 Sep 2020 16:50:34 -0400 Received: from mail.kernel.org ([198.145.29.99]:51368 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726879AbgIJUUz (ORCPT ); Thu, 10 Sep 2020 16:20:55 -0400 Received: from paulmck-ThinkPad-P72.home (unknown [50.45.173.55]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id E39D2221E2; Thu, 10 Sep 2020 20:20:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1599769255; bh=SfAmhvlfMQYT+jzOFWGoEAQ9AA14MQ9NYDdfLyXdGdQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=dgAf6k13tA2TgklDD0y3Tcg+HxUT81BD3jOCafAWbbCTboWDIH1o5agVzwuFpqwUa uuJCx26loMLLjm5578Cl4/TV/HJVeddio08DZSLEwepjHv1SBgsZCwA0p0z+Z/tHYF pl1nb0/NZq8Ef204JxWMZfxuXZz7pLbhHrvsFEEA= From: paulmck@kernel.org To: rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com, mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org, alexei.starovoitov@gmail.com, daniel@iogearbox.net, jolsa@redhat.com, bpf@vger.kernel.org, "Paul E. McKenney" Subject: [PATCH RFC tip/core/rcu 2/4] rcu-tasks: Use more aggressive polling for RCU Tasks Trace Date: Thu, 10 Sep 2020 13:20:50 -0700 Message-Id: <20200910202052.5073-2-paulmck@kernel.org> X-Mailer: git-send-email 2.9.5 In-Reply-To: <20200910201956.GA24190@paulmck-ThinkPad-P72> References: <20200910201956.GA24190@paulmck-ThinkPad-P72> Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org From: "Paul E. McKenney" The RCU Tasks Trace grace periods are too slow, as in 40x slower than those of RCU Tasks. This is due to my having assumed a one-second grace period was OK, and thus not having optimized any further. This commit provides the first step in this optimization process, namely by allowing the task_list scan backoff interval to be specified on a per-flavor basis, and then speeding up the scans for RCU Tasks Trace. However, kernels built with CONFIG_TASKS_TRACE_RCU_READ_MB=y continue to use the old slower backoff, consistent with that Kconfig option's goal of reducing IPIs. Link: https://lore.kernel.org/bpf/CAADnVQK_AiX+S_L_A4CQWT11XyveppBbQSQgH_qWGyzu_E8Yeg@mail.gmail.com/ Reported-by: Alexei Starovoitov Cc: Daniel Borkmann Cc: Jiri Olsa Cc: Signed-off-by: Paul E. McKenney --- kernel/rcu/tasks.h | 16 ++++++++++++++-- 1 file changed, 14 insertions(+), 2 deletions(-) diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h index 978508e..ad8c4f3 100644 --- a/kernel/rcu/tasks.h +++ b/kernel/rcu/tasks.h @@ -28,6 +28,7 @@ typedef void (*postgp_func_t)(struct rcu_tasks *rtp); * @kthread_ptr: This flavor's grace-period/callback-invocation kthread. * @gp_func: This flavor's grace-period-wait function. * @gp_state: Grace period's most recent state transition (debugging). + * @init_fract: Initial backoff sleep interval. * @gp_jiffies: Time of last @gp_state transition. * @gp_start: Most recent grace-period start in jiffies. * @n_gps: Number of grace periods completed since boot. @@ -48,6 +49,7 @@ struct rcu_tasks { struct wait_queue_head cbs_wq; raw_spinlock_t cbs_lock; int gp_state; + int init_fract; unsigned long gp_jiffies; unsigned long gp_start; unsigned long n_gps; @@ -329,8 +331,10 @@ static void rcu_tasks_wait_gp(struct rcu_tasks *rtp) */ lastreport = jiffies; - /* Start off with HZ/10 wait and slowly back off to 1 HZ wait. */ - fract = 10; + // Start off with initial wait and slowly back off to 1 HZ wait. + fract = rtp->init_fract; + if (fract > HZ) + fract = HZ; for (;;) { bool firstreport; @@ -553,6 +557,7 @@ EXPORT_SYMBOL_GPL(rcu_barrier_tasks); static int __init rcu_spawn_tasks_kthread(void) { + rcu_tasks.init_fract = 10; rcu_tasks.pregp_func = rcu_tasks_pregp_step; rcu_tasks.pertask_func = rcu_tasks_pertask; rcu_tasks.postscan_func = rcu_tasks_postscan; @@ -1163,6 +1168,13 @@ EXPORT_SYMBOL_GPL(rcu_barrier_tasks_trace); static int __init rcu_spawn_tasks_trace_kthread(void) { + if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB)) { + rcu_tasks_trace.init_fract = 10; + } else { + rcu_tasks_trace.init_fract = HZ / 5; + if (rcu_tasks_trace.init_fract <= 0) + rcu_tasks_trace.init_fract = 1; + } rcu_tasks_trace.pregp_func = rcu_tasks_trace_pregp_step; rcu_tasks_trace.pertask_func = rcu_tasks_trace_pertask; rcu_tasks_trace.postscan_func = rcu_tasks_trace_postscan;