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 442D9C4167B for ; Thu, 2 Dec 2021 00:43:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1355090AbhLBApc (ORCPT ); Wed, 1 Dec 2021 19:45:32 -0500 Received: from ams.source.kernel.org ([145.40.68.75]:37454 "EHLO ams.source.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1354683AbhLBAmc (ORCPT ); Wed, 1 Dec 2021 19:42:32 -0500 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 ams.source.kernel.org (Postfix) with ESMTPS id 18B18B821AB; Thu, 2 Dec 2021 00:39:05 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2706AC5833F; Thu, 2 Dec 2021 00:39:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1638405541; bh=aSUVez5pr95xwvB2cW6TJSk9s0oZI6dr5YoEdwcPgAk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=TvyP7JhGm7FZe65Hv+Gq/Cv3OWAr2vpSVq43dy79+Ap2c3vRWqrzD77A5EZPksdq1 19tM18+ZKS96GShBh0LVecxUGwDQNy4N6lQwDZvH1mOO7DMdNd50uDUIYHYiPmv26T /9+1E1mR6jCc3VHbRz2/c6mbIZdidfJib1vNNK0QE+x7/gKUY86u+0mXP3v8x9vpEN 7eaT4gBtL6wYTyvj6VOTKkjANTd5SO8al2PpY1ITKvZ6v5ZFajsQbn+Y3fRZUuKkA5 Xyeo7phV0aYFFVrj460UZfLbhKlGo54NlmvXbGyRJGGMSsgqCZN59ggO01bCnnNQ5L Jip0SwaXx7oQg== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 62EE35C1357; Wed, 1 Dec 2021 16:39:00 -0800 (PST) From: "Paul E. McKenney" To: rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com, mingo@kernel.org, jiangshanlai@gmail.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, "Paul E. McKenney" , Martin Lau , Neeraj Upadhyay Subject: [PATCH rcu 17/18] rcu-tasks: Use separate ->percpu_dequeue_lim for callback dequeueing Date: Wed, 1 Dec 2021 16:38:57 -0800 Message-Id: <20211202003858.3129628-17-paulmck@kernel.org> X-Mailer: git-send-email 2.31.1.189.g2e36527f23 In-Reply-To: <20211202003826.GA3129369@paulmck-ThinkPad-P17-Gen-1> References: <20211202003826.GA3129369@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 Decreasing the number of callback queues is a bit tricky because it is necessary to handle callbacks that were queued before the number of queues decreased, but which were not ready to invoke until afterwards. This commit takes a first step in this direction by maintaining a separate ->percpu_dequeue_lim to control callback dequeueing, in addition to the existing ->percpu_enqueue_lim which now controls only enqueueing. Reported-by: Martin Lau Cc: Neeraj Upadhyay Signed-off-by: Paul E. McKenney --- kernel/rcu/tasks.h | 15 ++++++++++----- 1 file changed, 10 insertions(+), 5 deletions(-) diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h index 1695da0f6985e..1fbffea6ae469 100644 --- a/kernel/rcu/tasks.h +++ b/kernel/rcu/tasks.h @@ -66,7 +66,8 @@ struct rcu_tasks_percpu { * @call_func: This flavor's call_rcu()-equivalent function. * @rtpcpu: This flavor's rcu_tasks_percpu structure. * @percpu_enqueue_shift: Shift down CPU ID this much when enqueuing callbacks. - * @percpu_enqueue_lim: Number of per-CPU callback queues in use. + * @percpu_enqueue_lim: Number of per-CPU callback queues in use for enqueuing. + * @percpu_dequeue_lim: Number of per-CPU callback queues in use for dequeuing. * @barrier_q_mutex: Serialize barrier operations. * @barrier_q_count: Number of queues being waited on. * @barrier_q_completion: Barrier wait/wakeup mechanism. @@ -96,6 +97,7 @@ struct rcu_tasks { struct rcu_tasks_percpu __percpu *rtpcpu; int percpu_enqueue_shift; int percpu_enqueue_lim; + int percpu_dequeue_lim; struct mutex barrier_q_mutex; atomic_t barrier_q_count; struct completion barrier_q_completion; @@ -121,6 +123,7 @@ static struct rcu_tasks rt_name = \ .name = n, \ .percpu_enqueue_shift = ilog2(CONFIG_NR_CPUS), \ .percpu_enqueue_lim = 1, \ + .percpu_dequeue_lim = 1, \ .barrier_q_mutex = __MUTEX_INITIALIZER(rt_name.barrier_q_mutex), \ .barrier_q_seq = (0UL - 50UL) << RCU_SEQ_CTR_SHIFT, \ .kname = #rt_name, \ @@ -223,6 +226,7 @@ static void cblist_init_generic(struct rcu_tasks *rtp) if (lim > nr_cpu_ids) lim = nr_cpu_ids; WRITE_ONCE(rtp->percpu_enqueue_shift, ilog2(nr_cpu_ids / lim)); + WRITE_ONCE(rtp->percpu_dequeue_lim, lim); smp_store_release(&rtp->percpu_enqueue_lim, lim); for_each_possible_cpu(cpu) { struct rcu_tasks_percpu *rtpcp = per_cpu_ptr(rtp->rtpcpu, cpu); @@ -290,6 +294,7 @@ static void call_rcu_tasks_generic(struct rcu_head *rhp, rcu_callback_t func, raw_spin_lock_irqsave(&rtp->cbs_gbl_lock, flags); if (rtp->percpu_enqueue_lim != nr_cpu_ids) { WRITE_ONCE(rtp->percpu_enqueue_shift, ilog2(nr_cpu_ids)); + WRITE_ONCE(rtp->percpu_enqueue_lim, nr_cpu_ids); smp_store_release(&rtp->percpu_enqueue_lim, nr_cpu_ids); pr_info("Switching %s to per-CPU callback queuing.\n", rtp->name); } @@ -343,7 +348,7 @@ static void rcu_barrier_tasks_generic(struct rcu_tasks *rtp) init_completion(&rtp->barrier_q_completion); atomic_set(&rtp->barrier_q_count, 2); for_each_possible_cpu(cpu) { - if (cpu >= smp_load_acquire(&rtp->percpu_enqueue_lim)) + if (cpu >= smp_load_acquire(&rtp->percpu_dequeue_lim)) break; rtpcp = per_cpu_ptr(rtp->rtpcpu, cpu); rtpcp->barrier_q_head.func = rcu_barrier_tasks_generic_cb; @@ -367,7 +372,7 @@ static int rcu_tasks_need_gpcb(struct rcu_tasks *rtp) unsigned long flags; int needgpcb = 0; - for (cpu = 0; cpu < smp_load_acquire(&rtp->percpu_enqueue_lim); cpu++) { + for (cpu = 0; cpu < smp_load_acquire(&rtp->percpu_dequeue_lim); cpu++) { struct rcu_tasks_percpu *rtpcp = per_cpu_ptr(rtp->rtpcpu, cpu); /* Advance and accelerate any new callbacks. */ @@ -399,11 +404,11 @@ static void rcu_tasks_invoke_cbs(struct rcu_tasks *rtp, struct rcu_tasks_percpu cpu = rtpcp->cpu; cpunext = cpu * 2 + 1; - if (cpunext < smp_load_acquire(&rtp->percpu_enqueue_lim)) { + if (cpunext < smp_load_acquire(&rtp->percpu_dequeue_lim)) { rtpcp_next = per_cpu_ptr(rtp->rtpcpu, cpunext); queue_work_on(cpunext, system_wq, &rtpcp_next->rtp_work); cpunext++; - if (cpunext < smp_load_acquire(&rtp->percpu_enqueue_lim)) { + if (cpunext < smp_load_acquire(&rtp->percpu_dequeue_lim)) { rtpcp_next = per_cpu_ptr(rtp->rtpcpu, cpunext); queue_work_on(cpunext, system_wq, &rtpcp_next->rtp_work); } -- 2.31.1.189.g2e36527f23