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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id C16C8C433EF for ; Tue, 19 Apr 2022 00:04:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236929AbiDSAHF (ORCPT ); Mon, 18 Apr 2022 20:07:05 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52786 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236870AbiDSAGJ (ORCPT ); Mon, 18 Apr 2022 20:06:09 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3B176237FA; Mon, 18 Apr 2022 17:03:28 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id A4726612DC; Tue, 19 Apr 2022 00:03:26 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4BEF1C385C7; Tue, 19 Apr 2022 00:03:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1650326605; bh=YwNURKj9mCIVjxikZL9NORCNyWNTo9uPcdOZhbmsazc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=RxdI+F6nO1OTvalSor++1mZLjYnYU8Y+aoppUZZ8k3QCqMWlamU/36mJsF+OZGNBT 86yeE7C3ZvDHvpaj+g00OR0hgH3ecm1bhH7UsBlPDRubzRgTS3lsq+RxR2/RIfna81 YkzC9dnjPQKUPrv6t1R6kGnkf+1qWhayp0KqEv/OvRFxFsbOGQgF53cP7oaXl3mIL3 E4R51gi4VREdCVH25xDY76DlJIpllyVqDGH5W8h9+IdyooPU8OP40d0xuiKLIyBLSz 4EAdjiGIH7Giw8Q3UaOSG5gMWXzIkKUqDZGUv95f1d9rW6u7kgPYTqHjdHyj6+LSZa 8kPVNIsHbcDww== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 6D2B45C30DF; Mon, 18 Apr 2022 17:03:24 -0700 (PDT) From: "Paul E. McKenney" To: rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com, rostedt@goodmis.org, "Paul E. McKenney" , Neeraj Upadhyay Subject: [PATCH rcu 18/21] srcu: Automatically determine size-transition strategy at boot Date: Mon, 18 Apr 2022 17:03:19 -0700 Message-Id: <20220419000322.3948903-18-paulmck@kernel.org> X-Mailer: git-send-email 2.31.1.189.g2e36527f23 In-Reply-To: <20220419000315.GA3948789@paulmck-ThinkPad-P17-Gen-1> References: <20220419000315.GA3948789@paulmck-ThinkPad-P17-Gen-1> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This commit adds a srcutree.convert_to_big option of zero that causes SRCU to decide at boot whether to wait for contention (small systems) or immediately expand to large (large systems). A new srcutree.big_cpu_lim (defaulting to 128) defines how many CPUs constitute a large system. Co-developed-by: Neeraj Upadhyay Signed-off-by: Neeraj Upadhyay Signed-off-by: Paul E. McKenney --- .../admin-guide/kernel-parameters.txt | 9 ++++++++ kernel/rcu/srcutree.c | 23 ++++++++++++++++--- 2 files changed, 29 insertions(+), 3 deletions(-) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 177e688768c0..057e30613d00 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -5608,6 +5608,14 @@ off: Disable mitigation and remove performance impact to RDRAND and RDSEED + srcutree.big_cpu_lim [KNL] + Specifies the number of CPUs constituting a + large system, such that srcu_struct structures + should immediately allocate an srcu_node array. + This kernel-boot parameter defaults to 128, but + takes effect only when srcutree.convert_to_big + is equal to zero. + srcutree.convert_to_big [KNL] Specifies under what conditions an SRCU tree srcu_struct structure will be converted to big @@ -5616,6 +5624,7 @@ 0: Never. 1: At init_srcu_struct() time. 2: When rcutorture decides to. + 3: Decide at boot time (default). 0x1X: Above plus if high contention. Either way, the srcu_node tree will be sized based diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c index 0bc6a0a3edee..b9dec26245e0 100644 --- a/kernel/rcu/srcutree.c +++ b/kernel/rcu/srcutree.c @@ -41,10 +41,10 @@ module_param(counter_wrap_check, ulong, 0444); /* * Control conversion to SRCU_SIZE_BIG: - * 0: Don't convert at all (default). + * 0: Don't convert at all. * 1: Convert at init_srcu_struct() time. * 2: Convert when rcutorture invokes srcu_torture_stats_print(). - * 3: Decide at boot time based on system shape. + * 3: Decide at boot time based on system shape (default). * 0x1x: Convert when excessive contention encountered. */ #define SRCU_SIZING_NONE 0 @@ -57,9 +57,13 @@ module_param(counter_wrap_check, ulong, 0444); #define SRCU_SIZING_IS_INIT() (SRCU_SIZING_IS(SRCU_SIZING_INIT)) #define SRCU_SIZING_IS_TORTURE() (SRCU_SIZING_IS(SRCU_SIZING_TORTURE)) #define SRCU_SIZING_IS_CONTEND() (convert_to_big & SRCU_SIZING_CONTEND) -static int convert_to_big = SRCU_SIZING_NONE; +static int convert_to_big = SRCU_SIZING_AUTO; module_param(convert_to_big, int, 0444); +/* Number of CPUs to trigger init_srcu_struct()-time transition to big. */ +static int big_cpu_lim __read_mostly = 128; +module_param(big_cpu_lim, int, 0444); + /* Contention events per jiffy to initiate transition to big. */ static int small_contention_lim __read_mostly = 100; module_param(small_contention_lim, int, 0444); @@ -1619,6 +1623,17 @@ void __init srcu_init(void) { struct srcu_struct *ssp; + /* Decide on srcu_struct-size strategy. */ + if (SRCU_SIZING_IS(SRCU_SIZING_AUTO)) { + if (nr_cpu_ids >= big_cpu_lim) { + convert_to_big = SRCU_SIZING_INIT; // Don't bother waiting for contention. + pr_info("%s: Setting srcu_struct sizes to big.\n", __func__); + } else { + convert_to_big = SRCU_SIZING_NONE | SRCU_SIZING_CONTEND; + pr_info("%s: Setting srcu_struct sizes based on contention.\n", __func__); + } + } + /* * Once that is set, call_srcu() can follow the normal path and * queue delayed work. This must follow RCU workqueues creation @@ -1629,6 +1644,8 @@ void __init srcu_init(void) ssp = list_first_entry(&srcu_boot_list, struct srcu_struct, work.work.entry); list_del_init(&ssp->work.work.entry); + if (SRCU_SIZING_IS(SRCU_SIZING_INIT) && ssp->srcu_size_state == SRCU_SIZE_SMALL) + ssp->srcu_size_state = SRCU_SIZE_ALLOC; queue_work(rcu_gp_wq, &ssp->work.work); } } -- 2.31.1.189.g2e36527f23