From patchwork Thu Sep 10 20:20:52 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: 1361982 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=cC54oQPV; dkim-atps=neutral Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by ozlabs.org (Postfix) with ESMTP id 4BnWGy3pyRz9sTv for ; Fri, 11 Sep 2020 06:50:02 +1000 (AEST) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727028AbgIJUt4 (ORCPT ); Thu, 10 Sep 2020 16:49:56 -0400 Received: from mail.kernel.org ([198.145.29.99]:51436 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726932AbgIJUU4 (ORCPT ); Thu, 10 Sep 2020 16:20:56 -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 8777B221EA; Thu, 10 Sep 2020 20:20:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1599769255; bh=EN8Ux1f40Gwbt7c8BI9OtZebo/fiQdq5Hs8XaO02MuA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=cC54oQPVSUHFiKwGk7Ytv6VTyCltQC2OYgYqIL1BN7knZVhOZKy9523c6vulodT6j uw1bWHuvSxSna8xmJFeZcdwzCCjpNygLqz4qpcurELJfipR6uu/j8tEQfaf+HlZuU9 qqhlv25t2ibIMDqKO/q7FgPwVVXM7rBpX933Q+4I= 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 4/4] rcu-tasks: Shorten per-grace-period sleep for RCU Tasks Trace Date: Thu, 10 Sep 2020 13:20:52 -0700 Message-Id: <20200910202052.5073-4-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 various RCU tasks flavors currently wait 100 milliseconds between each grace period in order to prevent CPU-bound loops and to favor efficiency over latency. However, RCU Tasks Trace needs to have a grace-period latency of roughly 25 milliseconds, which is completely infeasible given the 100-millisecond per-grace-period sleep. This commit therefore reduces this sleep duration to 5 milliseconds (or one jiffy, whichever is longer) in kernels built with CONFIG_TASKS_TRACE_RCU_READ_MB=y. 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 | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h index 2b4df23..a0eaed5 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). + * @gp_sleep: Per-grace-period sleep to prevent CPU-bound looping. * @init_fract: Initial backoff sleep interval. * @gp_jiffies: Time of last @gp_state transition. * @gp_start: Most recent grace-period start in jiffies. @@ -49,6 +50,7 @@ struct rcu_tasks { struct wait_queue_head cbs_wq; raw_spinlock_t cbs_lock; int gp_state; + int gp_sleep; int init_fract; unsigned long gp_jiffies; unsigned long gp_start; @@ -233,7 +235,7 @@ static int __noreturn rcu_tasks_kthread(void *arg) cond_resched(); } /* Paranoid sleep to keep this from entering a tight loop */ - schedule_timeout_idle(HZ/10); + schedule_timeout_idle(rtp->gp_sleep); set_tasks_gp_state(rtp, RTGS_WAIT_CBS); } @@ -557,6 +559,7 @@ EXPORT_SYMBOL_GPL(rcu_barrier_tasks); static int __init rcu_spawn_tasks_kthread(void) { + rcu_tasks.gp_sleep = HZ / 10; rcu_tasks.init_fract = 10; rcu_tasks.pregp_func = rcu_tasks_pregp_step; rcu_tasks.pertask_func = rcu_tasks_pertask; @@ -690,6 +693,7 @@ EXPORT_SYMBOL_GPL(rcu_barrier_tasks_rude); static int __init rcu_spawn_tasks_rude_kthread(void) { + rcu_tasks_rude.gp_sleep = HZ / 10; rcu_spawn_tasks_kthread_generic(&rcu_tasks_rude); return 0; } @@ -1170,8 +1174,12 @@ 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.gp_sleep = HZ / 10; rcu_tasks_trace.init_fract = 10; } else { + rcu_tasks_trace.gp_sleep = HZ / 200; + if (rcu_tasks_trace.gp_sleep <= 0) + rcu_tasks_trace.gp_sleep = 1; rcu_tasks_trace.init_fract = HZ / 5; if (rcu_tasks_trace.init_fract <= 0) rcu_tasks_trace.init_fract = 1;