From patchwork Sat Jul 29 14:27:34 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Joel Fernandes X-Patchwork-Id: 13333187 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 22A2DC001E0 for ; Sat, 29 Jul 2023 14:28:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231931AbjG2O2B (ORCPT ); Sat, 29 Jul 2023 10:28:01 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56482 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231899AbjG2O2A (ORCPT ); Sat, 29 Jul 2023 10:28:00 -0400 Received: from mail-io1-xd33.google.com (mail-io1-xd33.google.com [IPv6:2607:f8b0:4864:20::d33]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 722DC2686 for ; Sat, 29 Jul 2023 07:27:59 -0700 (PDT) Received: by mail-io1-xd33.google.com with SMTP id ca18e2360f4ac-7909307ecd1so16793439f.1 for ; Sat, 29 Jul 2023 07:27:59 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=joelfernandes.org; s=google; t=1690640879; x=1691245679; 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=0DIiXFGh73Irk8k8jfSTlgn3pzuU9BPg/xYZpIge3SA=; b=HsW5SYF4O4C1xrNtb8sm4pRTfnrrViTLGL7v+Gn/Ah7UCbBgZ2opbMTyrHiGdhoaEn gcNOhQcOz0QL2+Q2P4xe34TxFbuIhXlf9EExkeLpiag6Pz3CQW2C2PScS3kCNl4lYs5+ 6y9zYLXR2axTa6ZjwfeIofwo3CIgGps6icYMg= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1690640879; x=1691245679; 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=0DIiXFGh73Irk8k8jfSTlgn3pzuU9BPg/xYZpIge3SA=; b=Q+wB6kyQ0BNNINmu3gyCG52LR2w29q/LoNP08R5kBGng6tZ69mADG6XEy3SJm3Ngbc U6pepjeUplkhlxKQ+h/3mol4crCrzMIesCwfl9wRRJhSEQRc7Dhd0AZReNrxL6hWMFUq 57HBe7WC4OsJ7/VRQyely8UcX9p3yLN6uQjwZbMmfFn9RtJXvYxxospA+1kSYIg5GIy3 4DD+Y6nZq0JsXV5RqACJ6tUN9dGoNjTmlGFDtxRBqwGK7RGFOE93gsDxR17jesqwx/AC U0WR8yR7wyiQcpO0GAM9zA2L8sNAmP6nYHzI6RkYVexxjPpEL0MjZEeehYqpxhym1pAg ILyw== X-Gm-Message-State: ABy/qLYgOXlgq81YpKUIUKCq92iAcIHtXn22ugpMeNxz9iXHKkeaNqBd sRzdgUau7roMnDOKBzig4u6QVg== X-Google-Smtp-Source: APBJJlGcgY471iiH1xZgoLcliih5C9aIWb1vc/SB0/AH9RPxwH+38J4y3R/0f9F30AOyyZrL/iE+Xg== X-Received: by 2002:a5e:a90c:0:b0:787:34d:f223 with SMTP id c12-20020a5ea90c000000b00787034df223mr2373322iod.11.1690640878695; Sat, 29 Jul 2023 07:27:58 -0700 (PDT) Received: from joelboxx5.c.googlers.com.com (254.82.172.34.bc.googleusercontent.com. [34.172.82.254]) by smtp.gmail.com with ESMTPSA id q9-20020a0566380ec900b0042b35c7b8c5sm1855362jas.61.2023.07.29.07.27.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 29 Jul 2023 07:27:58 -0700 (PDT) From: "Joel Fernandes (Google)" To: linux-kernel@vger.kernel.org Cc: rcu@vger.kernel.org, paulmck@kernel.org, "Joel Fernandes (Google)" , Frederic Weisbecker , Neeraj Upadhyay , Josh Triplett , Boqun Feng , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , Zqiang Subject: [PATCH v2 4/5] tree/nocb: Improve readability of nocb_gp_wait() Date: Sat, 29 Jul 2023 14:27:34 +0000 Message-ID: <20230729142738.222208-5-joel@joelfernandes.org> X-Mailer: git-send-email 2.41.0.487.g6d72f3e995-goog In-Reply-To: <20230729142738.222208-1-joel@joelfernandes.org> References: <20230729142738.222208-1-joel@joelfernandes.org> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org The nocb_gp_wait() function contains logic to check each rdp's bypass list, flush if needed, and decide on wakeups. This makes the function hard to follow. Split out the bypass checking and flushing into a separate helper nocb_gp_flush_wake(). The new function encapsulates the logic to: - Check if the bypass needs to be flushed - Flush if needed - Return info on wakeups (lazy, bypass or none) nocb_gp_wait() now becomes simpler by calling the helper to handle the bypass flushing and waking logic. This splitting improves the readability and maintainability of the code by encapsulating related logic into a function with a clear purpose. Signed-off-by: Joel Fernandes (Google) --- kernel/rcu/tree_nocb.h | 113 ++++++++++++++++++++++++----------------- 1 file changed, 66 insertions(+), 47 deletions(-) diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h index 5598212d1f27..c805825c3f00 100644 --- a/kernel/rcu/tree_nocb.h +++ b/kernel/rcu/tree_nocb.h @@ -670,22 +670,68 @@ static void nocb_gp_sleep(struct rcu_data *my_rdp, int cpu) trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("EndSleep")); } +/* + * Given an rdp, flush its bypass list if needed and return information about + * if a deferred-wakeup needs to be organized depending on whether things are + * still in the bypass list. Also tell caller if the list was flushed and if it + * is still empty after any flushing. + */ +static int nocb_gp_flush_wake(struct rcu_data *rdp, bool *empty, bool *flush) +{ + long bypass_ncbs; + long lazy_ncbs; + unsigned long j = jiffies; + + trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("Check")); + lockdep_assert_held(&rdp->nocb_lock); + bypass_ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass); + lazy_ncbs = READ_ONCE(rdp->lazy_len); + + *flush = false; + *empty = false; + if (bypass_ncbs && (lazy_ncbs == bypass_ncbs) && + (time_after(j, READ_ONCE(rdp->nocb_bypass_first) + jiffies_till_flush) || + bypass_ncbs > 2 * qhimark)) { + *flush = true; + } else if (bypass_ncbs && (lazy_ncbs != bypass_ncbs) && + (time_after(j, READ_ONCE(rdp->nocb_bypass_first) + 1) || + bypass_ncbs > 2 * qhimark)) { + *flush = true; + } else if (!bypass_ncbs && rcu_segcblist_empty(&rdp->cblist)) { + *empty = true; + return RCU_NOCB_WAKE_NOT; + } + + if (*flush) { + // Bypass full or old, so flush it. + (void)rcu_nocb_try_flush_bypass(rdp, j); + bypass_ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass); + lazy_ncbs = READ_ONCE(rdp->lazy_len); + } + + if (bypass_ncbs) { + trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, + bypass_ncbs == lazy_ncbs ? TPS("Lazy") : TPS("Bypass")); + return (bypass_ncbs == lazy_ncbs ? RCU_NOCB_WAKE_LAZY : + RCU_NOCB_WAKE_BYPASS); + } + return RCU_NOCB_WAKE_NOT; +} + /* * No-CBs GP kthreads come here to wait for additional callbacks to show up * or for grace periods to end. */ static void nocb_gp_wait(struct rcu_data *my_rdp) { - bool bypass = false; int __maybe_unused cpu = my_rdp->cpu; unsigned long cur_gp_seq; unsigned long flags; bool gotcbs = false; - unsigned long j = jiffies; - bool lazy = false; bool needwait_gp = false; // This prevents actual uninitialized use. bool needwake; bool needwake_gp; + int defer_wake_type = RCU_NOCB_WAKE_NOT; struct rcu_data *rdp, *rdp_toggling = NULL; struct rcu_node *rnp; unsigned long wait_gp_seq = 0; // Suppress "use uninitialized" warning. @@ -712,44 +758,24 @@ static void nocb_gp_wait(struct rcu_data *my_rdp) * won't be ignored for long. */ list_for_each_entry(rdp, &my_rdp->nocb_head_rdp, nocb_entry_rdp) { - long bypass_ncbs; - bool flush_bypass = false; - long lazy_ncbs; + int defer_wake_type_one = RCU_NOCB_WAKE_NOT; + bool flushed; + bool empty; - trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("Check")); rcu_nocb_lock_irqsave(rdp, flags); - lockdep_assert_held(&rdp->nocb_lock); - bypass_ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass); - lazy_ncbs = READ_ONCE(rdp->lazy_len); + defer_wake_type_one = nocb_gp_flush_wake(rdp, &empty, &flushed); - if (bypass_ncbs && (lazy_ncbs == bypass_ncbs) && - (time_after(j, READ_ONCE(rdp->nocb_bypass_first) + jiffies_till_flush) || - bypass_ncbs > 2 * qhimark)) { - flush_bypass = true; - } else if (bypass_ncbs && (lazy_ncbs != bypass_ncbs) && - (time_after(j, READ_ONCE(rdp->nocb_bypass_first) + 1) || - bypass_ncbs > 2 * qhimark)) { - flush_bypass = true; - } else if (!bypass_ncbs && rcu_segcblist_empty(&rdp->cblist)) { - rcu_nocb_unlock_irqrestore(rdp, flags); - continue; /* No callbacks here, try next. */ - } + // We may need to do a deferred wakeup later for bypass/lazy + // So note down what we learnt from the rdp. + defer_wake_type = max(defer_wake_type_one, defer_wake_type); - if (flush_bypass) { - // Bypass full or old, so flush it. - (void)rcu_nocb_try_flush_bypass(rdp, j); - bypass_ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass); - lazy_ncbs = READ_ONCE(rdp->lazy_len); + // Did we make any updates to main cblist? If not, no + // non-deferred wake up to do for this rdp. + if (!flushed && empty) { + rcu_nocb_unlock_irqrestore(rdp, flags); + continue; } - if (bypass_ncbs) { - trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, - bypass_ncbs == lazy_ncbs ? TPS("Lazy") : TPS("Bypass")); - if (bypass_ncbs == lazy_ncbs) - lazy = true; - else - bypass = true; - } rnp = rdp->mynode; // Advance callbacks if helpful and low contention. @@ -792,23 +818,16 @@ static void nocb_gp_wait(struct rcu_data *my_rdp) rcu_gp_kthread_wake(); } - my_rdp->nocb_gp_bypass = bypass; + my_rdp->nocb_gp_bypass = (defer_wake_type == RCU_NOCB_WAKE_BYPASS); my_rdp->nocb_gp_gp = needwait_gp; my_rdp->nocb_gp_seq = needwait_gp ? wait_gp_seq : 0; // At least one child with non-empty ->nocb_bypass, so set // timer in order to avoid stranding its callbacks. - if (!rcu_nocb_poll) { - // If bypass list only has lazy CBs. Add a deferred lazy wake up. - if (lazy && !bypass) { - wake_nocb_gp_defer(my_rdp, RCU_NOCB_WAKE_LAZY, - TPS("WakeLazyIsDeferred")); - // Otherwise add a deferred bypass wake up. - } else if (bypass) { - wake_nocb_gp_defer(my_rdp, RCU_NOCB_WAKE_BYPASS, - TPS("WakeBypassIsDeferred")); - } - } + if (!rcu_nocb_poll && defer_wake_type != RCU_NOCB_WAKE_NOT) + wake_nocb_gp_defer(my_rdp, defer_wake_type, + defer_wake_type == RCU_NOCB_WAKE_LAZY ? + TPS("WakeLazyIsDeferred") : TPS("WakeBypassIsDeferred")); if (rcu_nocb_poll) { /* Polling, so trace if first poll in the series. */