From nobody Wed Dec 17 12:44:11 2025 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 E67DEC4167B for ; Tue, 28 Nov 2023 08:01:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234637AbjK1IBJ (ORCPT ); Tue, 28 Nov 2023 03:01:09 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58984 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1343963AbjK1IAh (ORCPT ); Tue, 28 Nov 2023 03:00:37 -0500 Received: from mail-lf1-x12c.google.com (mail-lf1-x12c.google.com [IPv6:2a00:1450:4864:20::12c]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 75B4CB6; Tue, 28 Nov 2023 00:00:42 -0800 (PST) Received: by mail-lf1-x12c.google.com with SMTP id 2adb3069b0e04-50abb83866bso6932977e87.3; Tue, 28 Nov 2023 00:00:42 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1701158441; x=1701763241; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=MRdqwIFL2uVW5SxPC7i3fG3JaqKAc+zofDkQy5XD79k=; b=LfhBQkt4wO0EbJX2OvRJREaSOnZEbNUkktBqO1TRXMgOZ8ds3NkB2YsMFzPlLmtLmY wBk5SyDZy4tQiciLSbv791qs56flA+8XRMJWbgrxJpNkrrxeskv8H37gkmRmXazphcW6 LKXj14loIRF0rTWMV3GuAPUcWNBh+zBL4m7U2N7+uV4CiHJ68Dx3VCYaBso3Me3B3bWw /RcXClN2pPmQTsf68A0giys4f+DhwnkRwgj3P0rtheFnll0oxTVLLYIShtYIK/3gzGuU J3dtw/zqc3IFuy8nEHs0+yXdh4JesRQmrhUnI8Y8kr66mf74JoQ00UN0XGDyI+mBpN+W WjBA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1701158441; x=1701763241; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=MRdqwIFL2uVW5SxPC7i3fG3JaqKAc+zofDkQy5XD79k=; b=V4x4lDDxhXBTebb9mjzmNjFdURqOPPLqJ0nae87okG7YgDDgEeGIMrlg1GnE1lxPRf W61rBva6utkhWmIke7xMzVc9r/KL5qi5CCFjnuV8XZpyDcLxGAMoJnwN2w63HSR1qZ1O hC3SXFi+foFgmdJBkrVhq1H1ClRfSLqF4MItDZzfciz5CC0WqVm4AaO36M6r2daHoJGp +blkhDEFNrFuLN3sjPLe+GUqGVzFRVPU2uOrcClQUgEZ/wnKQkMrgj+eC8amFrLlPsRc ocRQhfXOquleSMbecCFbEOJV/Yd+ZNl8BAzvZKjEDRjeDlbbdm7YCiM82JrVPdI7NnMk q/wA== X-Gm-Message-State: AOJu0YwTvdclA3soNl3y+WeV1FDYoNe4lDqvFwTdcK3ujOwnUSO4utk0 Wp5Q+GORhIVVBGSaTga2nG0= X-Google-Smtp-Source: AGHT+IHe6xi4biLqoNAaaRuvyFCyxXEagtGb5TcjgRABkz7K+RpGBmUMYSw1iQ20LwMVr1VBG52asQ== X-Received: by 2002:a05:6512:1282:b0:50b:ae9f:bf9c with SMTP id u2-20020a056512128200b0050bae9fbf9cmr5286278lfs.55.1701158440567; Tue, 28 Nov 2023 00:00:40 -0800 (PST) Received: from pc638.lan ([155.137.26.201]) by smtp.gmail.com with ESMTPSA id o16-20020ac24bd0000000b004fe202a5c7csm1765501lfq.135.2023.11.28.00.00.39 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 28 Nov 2023 00:00:40 -0800 (PST) From: "Uladzislau Rezki (Sony)" To: "Paul E . McKenney" Cc: RCU , Neeraj upadhyay , Boqun Feng , Hillf Danton , Joel Fernandes , LKML , Uladzislau Rezki , Oleksiy Avramchenko , Frederic Weisbecker Subject: [PATCH v3 5/7] rcu: Support direct wake-up of synchronize_rcu() users Date: Tue, 28 Nov 2023 09:00:31 +0100 Message-Id: <20231128080033.288050-6-urezki@gmail.com> X-Mailer: git-send-email 2.39.2 In-Reply-To: <20231128080033.288050-1-urezki@gmail.com> References: <20231128080033.288050-1-urezki@gmail.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" This patch introduces a small enhancement which allows to do a direct wake-up of synchronize_rcu() callers. It occurs after a completion of grace period, thus by the gp-kthread. Number of clients is limited by the hard-coded maximum allowed threshold. The remaining part, if still exists is deferred to a main worker. Signed-off-by: Uladzislau Rezki (Sony) --- kernel/rcu/tree.c | 39 +++++++++++++++++++++++++++++++++++++-- 1 file changed, 37 insertions(+), 2 deletions(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index d7b48996825f..69663a6d5050 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -1384,6 +1384,12 @@ static void rcu_poll_gp_seq_end_unlocked(unsigned lo= ng *snap) raw_spin_unlock_irqrestore_rcu_node(rnp, flags); } =20 +/* + * A max threshold for synchronize_rcu() users which are + * awaken directly by the rcu_gp_kthread(). Left part is + * deferred to the main worker. + */ +#define SR_MAX_USERS_WAKE_FROM_GP 5 #define SR_NORMAL_GP_WAIT_HEAD_MAX 5 =20 struct sr_wait_node { @@ -1617,7 +1623,8 @@ static DECLARE_WORK(sr_normal_gp_cleanup, rcu_sr_norm= al_gp_cleanup_work); */ static void rcu_sr_normal_gp_cleanup(void) { - struct llist_node *wait_tail; + struct llist_node *wait_tail, *head, *rcu; + int done =3D 0; =20 wait_tail =3D sr.srs_wait_tail; if (wait_tail =3D=3D NULL) @@ -1626,11 +1633,39 @@ static void rcu_sr_normal_gp_cleanup(void) sr.srs_wait_tail =3D NULL; ASSERT_EXCLUSIVE_WRITER(sr.srs_wait_tail); =20 + WARN_ON_ONCE(!rcu_sr_is_wait_head(wait_tail)); + head =3D wait_tail->next; + + /* + * Process (a) and (d) cases. See an illustration. Apart of + * that it handles the scenario when all clients are done, + * wait-head is released if last. The worker is not kicked. + */ + llist_for_each_safe(rcu, head, head) { + if (rcu_sr_is_wait_head(rcu)) { + if (!rcu->next) { + rcu_sr_put_wait_head(rcu); + wait_tail->next =3D NULL; + } else { + wait_tail->next =3D rcu; + } + + break; + } + + rcu_sr_normal_complete(rcu); + // It can be last, update a next on this step. + wait_tail->next =3D head; + + if (++done =3D=3D SR_MAX_USERS_WAKE_FROM_GP) + break; + } + // concurrent sr_normal_gp_cleanup work might observe this update. smp_store_release(&sr.srs_done_tail, wait_tail); ASSERT_EXCLUSIVE_WRITER(sr.srs_done_tail); =20 - if (wait_tail) + if (wait_tail->next) queue_work(system_highpri_wq, &sr_normal_gp_cleanup); } =20 --=20 2.39.2