From patchwork Tue Feb 20 18:31:12 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Uladzislau Rezki X-Patchwork-Id: 13564338 Received: from mail-lf1-f48.google.com (mail-lf1-f48.google.com [209.85.167.48]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id BFAA41272AD; Tue, 20 Feb 2024 18:31:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.167.48 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1708453882; cv=none; b=KNOEsZr809n25/WJGOG4wsQp92kjN7WQR93oc2QIvQeOYcFABIVtWhiYt+hdz78wnGL7QT+tIw2FtXecurlL98pkENzTIieD/BiOAD14vx+3h1ww+jPPbTLo8pQveEsAyqlinLwO4jWABLgkum+dYZQqTFp5yTigADebIsO2+F0= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1708453882; c=relaxed/simple; bh=+sM30cOyHqXSmmhxaV2sjUAEf1nC4m+PeirwUjejQqo=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=uKsKbgkyyWYhpEgvk/TUTdHcDsuuHUtTses99sDEhtUTWdRPGoyShLKfQiL2nM+Q0gfsZ4sIuIXZ5Gks4QSjeNC3EwBgAkC3CHJfbfaTr/jpfV7QSbiRGO8yVquLFjzCHKSxljaB7lMl/A2Mq+drPR7l3YrK/eRNTJtsTTaUwuc= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=lytMmJFk; arc=none smtp.client-ip=209.85.167.48 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="lytMmJFk" Received: by mail-lf1-f48.google.com with SMTP id 2adb3069b0e04-512ab55fde6so4139617e87.2; Tue, 20 Feb 2024 10:31:20 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1708453879; x=1709058679; 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=jOpDJiuEMajeibzl8V5uZUX1gqeJEBwIDoQaXh828aE=; b=lytMmJFkzEhXGCGzjPYPaUY+u5+v9PrKjqXTG3IGC+RAZhYn8M+X/9KVfHkcNU9ibO CM+FJ5gG09sGRoLhn7Je2SJiT0ZlryUpdOrW0HD5GQEZYSVTxYmslEEJJndcK0raDTQ3 cmN2j5VKVY9U5BPLmJB3M/SDgHpHYrMYAANiB8Yg3syD9nPMZLrh3OaOSfE2SUvHQ0Ou p7yiT+ivyWe0R/Zho/3iQPVKPjpEFClifH813D9pabpfi+VThIgb4lDDUQHgM/OS47R2 Q6TPdmYdbNTQwrNB1p27Akncl/sy4+Y2WFnWa3tkYWfmCejkMhsXVnEsIx7UQof/Yh8T PwEw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1708453879; x=1709058679; 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=jOpDJiuEMajeibzl8V5uZUX1gqeJEBwIDoQaXh828aE=; b=B5zMSMQCNLZ6NcQNy/EZv/1mrEiaJQZMm131YEMJ4CgE463ubJtjWWzk3KutnQatCM SkCjX8Drn4MO/JW+hN5q6k1SzXYsjusBhk6cOUiKHMGiYI2ARnOWLpvELYFUBnjpXfca ZyT6ouL9QWTNhz6sBz5NYKU6QAfoc0erIQXWhaG0lft4LWhegCBgjRjuqvWM7CClgHUa rmbVUAq51wI14LSwNe24gz7hBgRbk9Ou2hIs2OWfW9fQF0eifxHkb4/9k8IJWYJGwztK 2jL2beSCCTVMLl5be2gSJiRMw7jBOEhMSBJBdUiiDHa7AYvY2qSqUc0xZCyjWFJwJr55 mhzg== X-Forwarded-Encrypted: i=1; AJvYcCXoWb5XFEZegHA6BjGAuc3HCzaMaUR+HAZcHtdoA4uDzqcf+r0pZLyRVr0XofkubjIpG/378P8OX0B0jE/qtk+4M1vlwgXEWXkxhefV X-Gm-Message-State: AOJu0YxZa+jOx/vxvYU5TLwfk1FlZsi1yAm7lfcj/0Ez4agZtb4CaUTX 5OuGs3s2vArRLQCkv4IpKlAn0ndjkCD7oxOye79KY9+RhSXa+J9LAXROOtl5 X-Google-Smtp-Source: AGHT+IFEWEH+rV+eoGOniJBjuYuCBphY4QaFey8wMvcUlAbEtVKv1haHkL7sEnZi1q8cd7e/oYyLtg== X-Received: by 2002:a05:6512:708:b0:512:b372:4eed with SMTP id b8-20020a056512070800b00512b3724eedmr3947732lfs.8.1708453878610; Tue, 20 Feb 2024 10:31:18 -0800 (PST) Received: from pc638.lan (host-185-121-47-193.sydskane.nu. [185.121.47.193]) by smtp.gmail.com with ESMTPSA id b14-20020ac247ee000000b005118add498asm1365937lfp.130.2024.02.20.10.31.17 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 20 Feb 2024 10:31:18 -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 v5 1/4] rcu: Add data structures for synchronize_rcu() Date: Tue, 20 Feb 2024 19:31:12 +0100 Message-Id: <20240220183115.74124-2-urezki@gmail.com> X-Mailer: git-send-email 2.39.2 In-Reply-To: <20240220183115.74124-1-urezki@gmail.com> References: <20240220183115.74124-1-urezki@gmail.com> Precedence: bulk X-Mailing-List: rcu@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 The synchronize_rcu() call is going to be reworked, thus this patch adds dedicated fields into the rcu_state structure. Signed-off-by: Uladzislau Rezki (Sony) --- kernel/rcu/tree.h | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h index df48160b3136..b942b9437438 100644 --- a/kernel/rcu/tree.h +++ b/kernel/rcu/tree.h @@ -315,6 +315,13 @@ do { \ __set_current_state(TASK_RUNNING); \ } while (0) +#define SR_NORMAL_GP_WAIT_HEAD_MAX 5 + +struct sr_wait_node { + atomic_t inuse; + struct llist_node node; +}; + /* * RCU global state, including node hierarchy. This hierarchy is * represented in "heap" form in a dense array. The root (first level) @@ -400,6 +407,13 @@ struct rcu_state { /* Synchronize offline with */ /* GP pre-initialization. */ int nocb_is_setup; /* nocb is setup from boot */ + + /* synchronize_rcu() part. */ + struct llist_head srs_next; /* request a GP users. */ + struct llist_node *srs_wait_tail; /* wait for GP users. */ + struct llist_node *srs_done_tail; /* ready for GP users. */ + struct sr_wait_node srs_wait_nodes[SR_NORMAL_GP_WAIT_HEAD_MAX]; + struct work_struct srs_cleanup_work; }; /* Values for rcu_state structure's gp_flags field. */ From patchwork Tue Feb 20 18:31:13 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Uladzislau Rezki X-Patchwork-Id: 13564339 Received: from mail-lj1-f169.google.com (mail-lj1-f169.google.com [209.85.208.169]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8D8E5127B42; Tue, 20 Feb 2024 18:31:21 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.208.169 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1708453884; cv=none; b=CALfGtYfQ1LPlw92gANIIpt4TbSpKgpXODVt+MjozXTWehIjG15K4IVPDacCpi3TgXgcYRLWola9M3+XeOr/oj3+9fPphxpDH1IC3HKOOKPt9lXtll1rG5wX+ksOKSJQ0o1tRZx58bMN5vI/XS7212jkq3R7HJ2dysKtpHbrhWU= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1708453884; c=relaxed/simple; bh=FdF0mgTap9bXDrmQSaRzwCgS3LDsGplUhtEqGb0GcTQ=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=Vbbmo3iUrg3ui57Co9pXn50yonwrrksmZ0EpCe+yX7UaG9eEZreK1EurnsTbZsZFWyclGsB/DmVrCPlWaq8YDPiSEqBN59+53UV3Il29a6ulhXhkt8ccxjqPYn9fYwJ9MPQcC2OCemJlXcACz1keeg7GcnBWPlsQ4SPcdx1eHyE= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=F6XCHcoq; arc=none smtp.client-ip=209.85.208.169 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="F6XCHcoq" Received: by mail-lj1-f169.google.com with SMTP id 38308e7fff4ca-2d208be133bso60713851fa.2; Tue, 20 Feb 2024 10:31:21 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1708453880; x=1709058680; 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=wus0M0lyQQHcOlLysxUocxe/UwP6fnCb6fumk2LTjUE=; b=F6XCHcoqsMOsLi4lNao4Pbisp6mpJM1GecH4m4yT0AZoR9AVHepHbtzeqoo4oaoZIJ okIHB3hAeihWwe5VdZiKy42DkJsbsJVFL/1GPxZqSnWsp/OfFLJMbm1rNfppF90DkhBv NGxmDZI9ySfJvFjGrhuSusaf+z0+F/ime0OmXVWCUpNWEMisy5CW6AsczaUA8wiFC89v sG/nAmHgcWfjIPOUCrEUBaLB2BlZhNwR3gE7hrDR28z3MIm9zIARw6u/6LcpVeJ3C1YV lpg0EoyBw3bXtRD76vXxJDfeGBJSyZj+m8SBEH36C2brPvEWKhVHhSScd1+tZoEdqSO3 M4QA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1708453880; x=1709058680; 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=wus0M0lyQQHcOlLysxUocxe/UwP6fnCb6fumk2LTjUE=; b=MbmCcCC+0jj5gmySD+UzJrMcC9EqNgt7sqDnCwWS1W+l0IpIMcujSOgomCUyIJephd fEjXTEKb6Anj5BPhlWTajS/B2tY29ajAOuxqzP9KCVHy939bLryPAmANDYa0JVYHKpYD IikGdi2bXTt/Ebuv0wCZLdHHLDGX+YIlKLiy8fqw0aYN9eN+GDsNXMAQ9xFavgKKGAIY XQ10OYaNBwqFo9KITLYAR0Vl3f9ME2l8q5CQFaxOiRqDyI7UuhgB56NC/jKVVumOCBWk k0BpcPUKyQc5uMX3oWXYJHh1tBp7tFMIJSaC0cvSt2UuxWU//l3TVkF8AjMq4NWbVgdl 7V9g== X-Forwarded-Encrypted: i=1; AJvYcCX+eM2o4909rq4xe5CcrCnKI1tA1XLVPe8GnpkFMp9ltTqK+wBYND4FLm+lmbXTDT1joXzlsHRd41pvRvKj4J1KXLfLt83Na5bdak7I X-Gm-Message-State: AOJu0YxT6t+rNM6qy63iPxBzkU3QmBc6xaYUqtzaGk9T4gaYgeGCnw5o dq3JSiXeKUFnzMa9eIuLqxEUcpNqLGlzQ2APt3zR1zIlnnkI0X/K X-Google-Smtp-Source: AGHT+IF869iG7UewWJD16vnzP5Kezt7YBbNT+sy5+ZXKwMYTCLeX8ifpPhPoJLMRHaNM6yCQejQglQ== X-Received: by 2002:a05:6512:3a5:b0:512:be45:2b9 with SMTP id v5-20020a05651203a500b00512be4502b9mr2995147lfp.45.1708453879477; Tue, 20 Feb 2024 10:31:19 -0800 (PST) Received: from pc638.lan (host-185-121-47-193.sydskane.nu. [185.121.47.193]) by smtp.gmail.com with ESMTPSA id b14-20020ac247ee000000b005118add498asm1365937lfp.130.2024.02.20.10.31.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 20 Feb 2024 10:31:19 -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 v5 2/4] rcu: Reduce synchronize_rcu() latency Date: Tue, 20 Feb 2024 19:31:13 +0100 Message-Id: <20240220183115.74124-3-urezki@gmail.com> X-Mailer: git-send-email 2.39.2 In-Reply-To: <20240220183115.74124-1-urezki@gmail.com> References: <20240220183115.74124-1-urezki@gmail.com> Precedence: bulk X-Mailing-List: rcu@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 A call to a synchronize_rcu() can be optimized from a latency point of view. Workloads which depend on this can benefit of it. The delay of wakeme_after_rcu() callback, which unblocks a waiter, depends on several factors: - how fast a process of offloading is started. Combination of: - !CONFIG_RCU_NOCB_CPU/CONFIG_RCU_NOCB_CPU; - !CONFIG_RCU_LAZY/CONFIG_RCU_LAZY; - other. - when started, invoking path is interrupted due to: - time limit; - need_resched(); - if limit is reached. - where in a nocb list it is located; - how fast previous callbacks completed; Example: 1. On our embedded devices i can easily trigger the scenario when it is a last in the list out of ~3600 callbacks: <...>-29 [001] d..1. 21950.145313: rcu_batch_start: rcu_preempt CBs=3613 bl=28 ... <...>-29 [001] ..... 21950.152578: rcu_invoke_callback: rcu_preempt rhp=00000000b2d6dee8 func=__free_vm_area_struct.cfi_jt <...>-29 [001] ..... 21950.152579: rcu_invoke_callback: rcu_preempt rhp=00000000a446f607 func=__free_vm_area_struct.cfi_jt <...>-29 [001] ..... 21950.152580: rcu_invoke_callback: rcu_preempt rhp=00000000a5cab03b func=__free_vm_area_struct.cfi_jt <...>-29 [001] ..... 21950.152581: rcu_invoke_callback: rcu_preempt rhp=0000000013b7e5ee func=__free_vm_area_struct.cfi_jt <...>-29 [001] ..... 21950.152582: rcu_invoke_callback: rcu_preempt rhp=000000000a8ca6f9 func=__free_vm_area_struct.cfi_jt <...>-29 [001] ..... 21950.152583: rcu_invoke_callback: rcu_preempt rhp=000000008f162ca8 func=wakeme_after_rcu.cfi_jt <...>-29 [001] d..1. 21950.152625: rcu_batch_end: rcu_preempt CBs-invoked=3612 idle=.... 2. We use cpuset/cgroup to classify tasks and assign them into different cgroups. For example "backgrond" group which binds tasks only to little CPUs or "foreground" which makes use of all CPUs. Tasks can be migrated between groups by a request if an acceleration is needed. See below an example how "surfaceflinger" task gets migrated. Initially it is located in the "system-background" cgroup which allows to run only on little cores. In order to speed it up it can be temporary moved into "foreground" cgroup which allows to use big/all CPUs: cgroup_attach_task(): -> cgroup_migrate_execute() -> cpuset_can_attach() -> percpu_down_write() -> rcu_sync_enter() -> synchronize_rcu() -> now move tasks to the new cgroup. -> cgroup_migrate_finish() rcuop/1-29 [000] ..... 7030.528570: rcu_invoke_callback: rcu_preempt rhp=00000000461605e0 func=wakeme_after_rcu.cfi_jt PERFD-SERVER-1855 [000] d..1. 7030.530293: cgroup_attach_task: dst_root=3 dst_id=22 dst_level=1 dst_path=/foreground pid=1900 comm=surfaceflinger TimerDispatch-2768 [002] d..5. 7030.537542: sched_migrate_task: comm=surfaceflinger pid=1900 prio=98 orig_cpu=0 dest_cpu=4 "Boosting a task" depends on synchronize_rcu() latency: - first trace shows a completion of synchronize_rcu(); - second shows attaching a task to a new group; - last shows a final step when migration occurs. 3. To address this drawback, maintain a separate track that consists of synchronize_rcu() callers only. After completion of a grace period users are deferred to a dedicated worker to process requests. 4. This patch reduces the latency of synchronize_rcu() approximately by ~30-40% on synthetic tests. The real test case, camera launch time, shows(time is in milliseconds): 1-run 542 vs 489 improvement 9% 2-run 540 vs 466 improvement 13% 3-run 518 vs 468 improvement 9% 4-run 531 vs 457 improvement 13% 5-run 548 vs 475 improvement 13% 6-run 509 vs 484 improvement 4% Synthetic test(no "noise" from other callbacks): Hardware: x86_64 64 CPUs, 64GB of memory Linux-6.6 - 10K tasks(simultaneous); - each task does(1000 loops) synchronize_rcu(); kfree(p); default: CONFIG_RCU_NOCB_CPU: takes 54 seconds to complete all users; patch: CONFIG_RCU_NOCB_CPU: takes 35 seconds to complete all users. Running 60K gives approximately same results on my setup. Please note it is without any interaction with another type of callbacks, otherwise it will impact a lot a default case. 5. By default it is disabled. To enable this perform one of the below sequence: echo 1 > /sys/module/rcutree/parameters/rcu_normal_wake_from_gp or pass a boot parameter "rcutree.rcu_normal_wake_from_gp=1" Reviewed-by: Frederic Weisbecker Co-developed-by: Neeraj Upadhyay Signed-off-by: Uladzislau Rezki (Sony) --- .../admin-guide/kernel-parameters.txt | 14 + kernel/rcu/tree.c | 331 +++++++++++++++++- kernel/rcu/tree_exp.h | 2 +- 3 files changed, 345 insertions(+), 2 deletions(-) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 2244aa0a013b..7ca84cf7b4f4 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -5059,6 +5059,20 @@ delay, memory pressure or callback list growing too big. + rcutree.rcu_normal_wake_from_gp= [KNL] + Reduces a latency of synchronize_rcu() call. This approach + maintains its own track of synchronize_rcu() callers, so it + does not interact with regular callbacks because it does not + use a call_rcu[_hurry]() path. Please note, this is for a + normal grace period. + + How to enable it: + + echo 1 > /sys/module/rcutree/parameters/rcu_normal_wake_from_gp + or pass a boot parameter "rcutree.rcu_normal_wake_from_gp=1" + + Default is 0. + rcuscale.gp_async= [KNL] Measure performance of asynchronous grace-period primitives such as call_rcu(). diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index c8980d76f402..1328da63c3cd 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -75,6 +75,7 @@ #define MODULE_PARAM_PREFIX "rcutree." /* Data structures. */ +static void rcu_sr_normal_gp_cleanup_work(struct work_struct *); static DEFINE_PER_CPU_SHARED_ALIGNED(struct rcu_data, rcu_data) = { .gpwrap = true, @@ -93,6 +94,8 @@ static struct rcu_state rcu_state = { .exp_mutex = __MUTEX_INITIALIZER(rcu_state.exp_mutex), .exp_wake_mutex = __MUTEX_INITIALIZER(rcu_state.exp_wake_mutex), .ofl_lock = __ARCH_SPIN_LOCK_UNLOCKED, + .srs_cleanup_work = __WORK_INITIALIZER(rcu_state.srs_cleanup_work, + rcu_sr_normal_gp_cleanup_work), }; /* Dump rcu_node combining tree at boot to verify correct setup. */ @@ -1422,6 +1425,282 @@ static void rcu_poll_gp_seq_end_unlocked(unsigned long *snap) raw_spin_unlock_irqrestore_rcu_node(rnp, flags); } +/* + * There is a single llist, which is used for handling + * synchronize_rcu() users' enqueued rcu_synchronize nodes. + * Within this llist, there are two tail pointers: + * + * wait tail: Tracks the set of nodes, which need to + * wait for the current GP to complete. + * done tail: Tracks the set of nodes, for which grace + * period has elapsed. These nodes processing + * will be done as part of the cleanup work + * execution by a kworker. + * + * At every grace period init, a new wait node is added + * to the llist. This wait node is used as wait tail + * for this new grace period. Given that there are a fixed + * number of wait nodes, if all wait nodes are in use + * (which can happen when kworker callback processing + * is delayed) and additional grace period is requested. + * This means, a system is slow in processing callbacks. + * + * TODO: If a slow processing is detected, a first node + * in the llist should be used as a wait-tail for this + * grace period, therefore users which should wait due + * to a slow process are handled by _this_ grace period + * and not next. + * + * Below is an illustration of how the done and wait + * tail pointers move from one set of rcu_synchronize nodes + * to the other, as grace periods start and finish and + * nodes are processed by kworker. + * + * + * a. Initial llist callbacks list: + * + * +----------+ +--------+ +-------+ + * | | | | | | + * | head |---------> | cb2 |--------->| cb1 | + * | | | | | | + * +----------+ +--------+ +-------+ + * + * + * + * b. New GP1 Start: + * + * WAIT TAIL + * | + * | + * v + * +----------+ +--------+ +--------+ +-------+ + * | | | | | | | | + * | head ------> wait |------> cb2 |------> | cb1 | + * | | | head1 | | | | | + * +----------+ +--------+ +--------+ +-------+ + * + * + * + * c. GP completion: + * + * WAIT_TAIL == DONE_TAIL + * + * DONE TAIL + * | + * | + * v + * +----------+ +--------+ +--------+ +-------+ + * | | | | | | | | + * | head ------> wait |------> cb2 |------> | cb1 | + * | | | head1 | | | | | + * +----------+ +--------+ +--------+ +-------+ + * + * + * + * d. New callbacks and GP2 start: + * + * WAIT TAIL DONE TAIL + * | | + * | | + * v v + * +----------+ +------+ +------+ +------+ +-----+ +-----+ +-----+ + * | | | | | | | | | | | | | | + * | head ------> wait |--->| cb4 |--->| cb3 |--->|wait |--->| cb2 |--->| cb1 | + * | | | head2| | | | | |head1| | | | | + * +----------+ +------+ +------+ +------+ +-----+ +-----+ +-----+ + * + * + * + * e. GP2 completion: + * + * WAIT_TAIL == DONE_TAIL + * DONE TAIL + * | + * | + * v + * +----------+ +------+ +------+ +------+ +-----+ +-----+ +-----+ + * | | | | | | | | | | | | | | + * | head ------> wait |--->| cb4 |--->| cb3 |--->|wait |--->| cb2 |--->| cb1 | + * | | | head2| | | | | |head1| | | | | + * +----------+ +------+ +------+ +------+ +-----+ +-----+ +-----+ + * + * + * While the llist state transitions from d to e, a kworker + * can start executing rcu_sr_normal_gp_cleanup_work() and + * can observe either the old done tail (@c) or the new + * done tail (@e). So, done tail updates and reads need + * to use the rel-acq semantics. If the concurrent kworker + * observes the old done tail, the newly queued work + * execution will process the updated done tail. If the + * concurrent kworker observes the new done tail, then + * the newly queued work will skip processing the done + * tail, as workqueue semantics guarantees that the new + * work is executed only after the previous one completes. + * + * f. kworker callbacks processing complete: + * + * + * DONE TAIL + * | + * | + * v + * +----------+ +--------+ + * | | | | + * | head ------> wait | + * | | | head2 | + * +----------+ +--------+ + * + */ +static bool rcu_sr_is_wait_head(struct llist_node *node) +{ + return &(rcu_state.srs_wait_nodes)[0].node <= node && + node <= &(rcu_state.srs_wait_nodes)[SR_NORMAL_GP_WAIT_HEAD_MAX - 1].node; +} + +static struct llist_node *rcu_sr_get_wait_head(void) +{ + struct sr_wait_node *sr_wn; + int i; + + for (i = 0; i < SR_NORMAL_GP_WAIT_HEAD_MAX; i++) { + sr_wn = &(rcu_state.srs_wait_nodes)[i]; + + if (!atomic_cmpxchg_acquire(&sr_wn->inuse, 0, 1)) + return &sr_wn->node; + } + + return NULL; +} + +static void rcu_sr_put_wait_head(struct llist_node *node) +{ + struct sr_wait_node *sr_wn = container_of(node, struct sr_wait_node, node); + atomic_set_release(&sr_wn->inuse, 0); +} + +/* Disabled by default. */ +static int rcu_normal_wake_from_gp; +module_param(rcu_normal_wake_from_gp, int, 0644); + +static void rcu_sr_normal_complete(struct llist_node *node) +{ + struct rcu_synchronize *rs = container_of( + (struct rcu_head *) node, struct rcu_synchronize, head); + unsigned long oldstate = (unsigned long) rs->head.func; + + WARN_ONCE(IS_ENABLED(CONFIG_PROVE_RCU) && + !poll_state_synchronize_rcu(oldstate), + "A full grace period is not passed yet: %lu", + rcu_seq_diff(get_state_synchronize_rcu(), oldstate)); + + /* Finally. */ + complete(&rs->completion); +} + +static void rcu_sr_normal_gp_cleanup_work(struct work_struct *work) +{ + struct llist_node *done, *rcu, *next, *head; + + /* + * This work execution can potentially execute + * while a new done tail is being updated by + * grace period kthread in rcu_sr_normal_gp_cleanup(). + * So, read and updates of done tail need to + * follow acq-rel semantics. + * + * Given that wq semantics guarantees that a single work + * cannot execute concurrently by multiple kworkers, + * the done tail list manipulations are protected here. + */ + done = smp_load_acquire(&rcu_state.srs_done_tail); + if (!done) + return; + + WARN_ON_ONCE(!rcu_sr_is_wait_head(done)); + head = done->next; + done->next = NULL; + + /* + * The dummy node, which is pointed to by the + * done tail which is acq-read above is not removed + * here. This allows lockless additions of new + * rcu_synchronize nodes in rcu_sr_normal_add_req(), + * while the cleanup work executes. The dummy + * nodes is removed, in next round of cleanup + * work execution. + */ + llist_for_each_safe(rcu, next, head) { + if (!rcu_sr_is_wait_head(rcu)) { + rcu_sr_normal_complete(rcu); + continue; + } + + rcu_sr_put_wait_head(rcu); + } +} + +/* + * Helper function for rcu_gp_cleanup(). + */ +static void rcu_sr_normal_gp_cleanup(void) +{ + struct llist_node *wait_tail; + + wait_tail = rcu_state.srs_wait_tail; + if (wait_tail == NULL) + return; + + rcu_state.srs_wait_tail = NULL; + ASSERT_EXCLUSIVE_WRITER(rcu_state.srs_wait_tail); + + // concurrent sr_normal_gp_cleanup work might observe this update. + smp_store_release(&rcu_state.srs_done_tail, wait_tail); + ASSERT_EXCLUSIVE_WRITER(rcu_state.srs_done_tail); + + if (wait_tail) + queue_work(system_highpri_wq, &rcu_state.srs_cleanup_work); +} + +/* + * Helper function for rcu_gp_init(). + */ +static bool rcu_sr_normal_gp_init(void) +{ + struct llist_node *first; + struct llist_node *wait_head; + bool start_new_poll = false; + + first = READ_ONCE(rcu_state.srs_next.first); + if (!first || rcu_sr_is_wait_head(first)) + return start_new_poll; + + wait_head = rcu_sr_get_wait_head(); + if (!wait_head) { + // Kick another GP to retry. + start_new_poll = true; + return start_new_poll; + } + + /* Inject a wait-dummy-node. */ + llist_add(wait_head, &rcu_state.srs_next); + + /* + * A waiting list of rcu_synchronize nodes should be empty on + * this step, since a GP-kthread, rcu_gp_init() -> gp_cleanup(), + * rolls it over. If not, it is a BUG, warn a user. + */ + WARN_ON_ONCE(rcu_state.srs_wait_tail != NULL); + rcu_state.srs_wait_tail = wait_head; + ASSERT_EXCLUSIVE_WRITER(rcu_state.srs_wait_tail); + + return start_new_poll; +} + +static void rcu_sr_normal_add_req(struct rcu_synchronize *rs) +{ + llist_add((struct llist_node *) &rs->head, &rcu_state.srs_next); +} + /* * Initialize a new grace period. Return false if no grace period required. */ @@ -1432,6 +1711,7 @@ static noinline_for_stack bool rcu_gp_init(void) unsigned long mask; struct rcu_data *rdp; struct rcu_node *rnp = rcu_get_root(); + bool start_new_poll; WRITE_ONCE(rcu_state.gp_activity, jiffies); raw_spin_lock_irq_rcu_node(rnp); @@ -1456,10 +1736,24 @@ static noinline_for_stack bool rcu_gp_init(void) /* Record GP times before starting GP, hence rcu_seq_start(). */ rcu_seq_start(&rcu_state.gp_seq); ASSERT_EXCLUSIVE_WRITER(rcu_state.gp_seq); + start_new_poll = rcu_sr_normal_gp_init(); trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("start")); rcu_poll_gp_seq_start(&rcu_state.gp_seq_polled_snap); raw_spin_unlock_irq_rcu_node(rnp); + /* + * The "start_new_poll" is set to true, only when this GP is not able + * to handle anything and there are outstanding users. It happens when + * the rcu_sr_normal_gp_init() function was not able to insert a dummy + * separator to the llist, because there were no left any dummy-nodes. + * + * Number of dummy-nodes is fixed, it could be that we are run out of + * them, if so we start a new pool request to repeat a try. It is rare + * and it means that a system is doing a slow processing of callbacks. + */ + if (start_new_poll) + (void) start_poll_synchronize_rcu(); + /* * Apply per-leaf buffered online and offline operations to * the rcu_node tree. Note that this new grace period need not @@ -1825,6 +2119,9 @@ static noinline void rcu_gp_cleanup(void) } raw_spin_unlock_irq_rcu_node(rnp); + // Make synchronize_rcu() users aware of the end of old grace period. + rcu_sr_normal_gp_cleanup(); + // If strict, make all CPUs aware of the end of the old grace period. if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD)) on_each_cpu(rcu_strict_gp_boundary, NULL, 0); @@ -3559,6 +3856,38 @@ static int rcu_blocking_is_gp(void) return true; } +/* + * Helper function for the synchronize_rcu() API. + */ +static void synchronize_rcu_normal(void) +{ + struct rcu_synchronize rs; + + if (!READ_ONCE(rcu_normal_wake_from_gp)) { + wait_rcu_gp(call_rcu_hurry); + return; + } + + init_rcu_head_on_stack(&rs.head); + init_completion(&rs.completion); + + /* + * This code might be preempted, therefore take a GP + * snapshot before adding a request. + */ + if (IS_ENABLED(CONFIG_PROVE_RCU)) + rs.head.func = (void *) get_state_synchronize_rcu(); + + rcu_sr_normal_add_req(&rs); 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[185.121.47.193]) by smtp.gmail.com with ESMTPSA id b14-20020ac247ee000000b005118add498asm1365937lfp.130.2024.02.20.10.31.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 20 Feb 2024 10:31:19 -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 v5 3/4] rcu: Add a trace event for synchronize_rcu_normal() Date: Tue, 20 Feb 2024 19:31:14 +0100 Message-Id: <20240220183115.74124-4-urezki@gmail.com> X-Mailer: git-send-email 2.39.2 In-Reply-To: <20240220183115.74124-1-urezki@gmail.com> References: <20240220183115.74124-1-urezki@gmail.com> Precedence: bulk X-Mailing-List: rcu@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Add an rcu_sr_normal() trace event. It takes three arguments first one is the name of RCU flavour, second one is a user id which triggeres synchronize_rcu_normal() and last one is an event. There are two traces in the synchronize_rcu_normal(). On entry, when a new request is registered and on exit point when request is completed. Please note, CONFIG_RCU_TRACE=y is required to activate traces. Signed-off-by: Uladzislau Rezki (Sony) --- include/trace/events/rcu.h | 27 +++++++++++++++++++++++++++ kernel/rcu/tree.c | 7 ++++++- 2 files changed, 33 insertions(+), 1 deletion(-) diff --git a/include/trace/events/rcu.h b/include/trace/events/rcu.h index 2ef9c719772a..31b3e0d3e65f 100644 --- a/include/trace/events/rcu.h +++ b/include/trace/events/rcu.h @@ -707,6 +707,33 @@ TRACE_EVENT_RCU(rcu_invoke_kfree_bulk_callback, __entry->rcuname, __entry->p, __entry->nr_records) ); +/* + * Tracepoint for a normal synchronize_rcu() states. The first argument + * is the RCU flavor, the second argument is a pointer to rcu_head the + * last one is an event. + */ +TRACE_EVENT_RCU(rcu_sr_normal, + + TP_PROTO(const char *rcuname, struct rcu_head *rhp, const char *srevent), + + TP_ARGS(rcuname, rhp, srevent), + + TP_STRUCT__entry( + __field(const char *, rcuname) + __field(void *, rhp) + __field(const char *, srevent) + ), + + TP_fast_assign( + __entry->rcuname = rcuname; + __entry->rhp = rhp; + __entry->srevent = srevent; + ), + + TP_printk("%s rhp=0x%p event=%s", + __entry->rcuname, __entry->rhp, __entry->srevent) +); + /* * Tracepoint for exiting rcu_do_batch after RCU callbacks have been * invoked. 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[185.121.47.193]) by smtp.gmail.com with ESMTPSA id b14-20020ac247ee000000b005118add498asm1365937lfp.130.2024.02.20.10.31.20 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 20 Feb 2024 10:31:20 -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 v5 4/4] rcu: Support direct wake-up of synchronize_rcu() users Date: Tue, 20 Feb 2024 19:31:15 +0100 Message-Id: <20240220183115.74124-5-urezki@gmail.com> X-Mailer: git-send-email 2.39.2 In-Reply-To: <20240220183115.74124-1-urezki@gmail.com> References: <20240220183115.74124-1-urezki@gmail.com> Precedence: bulk X-Mailing-List: rcu@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 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 | 31 +++++++++++++++++++++++++++++-- kernel/rcu/tree.h | 6 ++++++ 2 files changed, 35 insertions(+), 2 deletions(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 3bf6b3c5ef05..31f3a61f9c38 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -1644,7 +1644,8 @@ static void rcu_sr_normal_gp_cleanup_work(struct work_struct *work) */ static void rcu_sr_normal_gp_cleanup(void) { - struct llist_node *wait_tail; + struct llist_node *wait_tail, *next, *rcu; + int done = 0; wait_tail = rcu_state.srs_wait_tail; if (wait_tail == NULL) @@ -1652,12 +1653,38 @@ static void rcu_sr_normal_gp_cleanup(void) rcu_state.srs_wait_tail = NULL; ASSERT_EXCLUSIVE_WRITER(rcu_state.srs_wait_tail); + WARN_ON_ONCE(!rcu_sr_is_wait_head(wait_tail)); + + /* + * 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, next, wait_tail->next) { + if (rcu_sr_is_wait_head(rcu)) { + if (!rcu->next) { + rcu_sr_put_wait_head(rcu); + wait_tail->next = NULL; + } else { + wait_tail->next = rcu; + } + + break; + } + + rcu_sr_normal_complete(rcu); + // It can be last, update a next on this step. + wait_tail->next = next; + + if (++done == SR_MAX_USERS_WAKE_FROM_GP) + break; + } // concurrent sr_normal_gp_cleanup work might observe this update. smp_store_release(&rcu_state.srs_done_tail, wait_tail); ASSERT_EXCLUSIVE_WRITER(rcu_state.srs_done_tail); - if (wait_tail) + if (wait_tail->next) queue_work(system_highpri_wq, &rcu_state.srs_cleanup_work); } diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h index b942b9437438..2832787cee1d 100644 --- a/kernel/rcu/tree.h +++ b/kernel/rcu/tree.h @@ -315,6 +315,12 @@ do { \ __set_current_state(TASK_RUNNING); \ } while (0) +/* + * 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 struct sr_wait_node {