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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 78247C433FE for ; Fri, 1 Oct 2021 17:50:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5FD0161A10 for ; Fri, 1 Oct 2021 17:50:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1355472AbhJARw2 (ORCPT ); Fri, 1 Oct 2021 13:52:28 -0400 Received: from foss.arm.com ([217.140.110.172]:49460 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1355467AbhJARw1 (ORCPT ); Fri, 1 Oct 2021 13:52:27 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id DB6BE106F; Fri, 1 Oct 2021 10:50:42 -0700 (PDT) Received: from e113632-lin (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 3AD573F70D; Fri, 1 Oct 2021 10:50:41 -0700 (PDT) From: Valentin Schneider To: Frederic Weisbecker , "Paul E . McKenney" Cc: LKML , Frederic Weisbecker , Sebastian Andrzej Siewior , Peter Zijlstra , Uladzislau Rezki , Thomas Gleixner , Boqun Feng , Neeraj Upadhyay , Josh Triplett , Joel Fernandes , rcu@vger.kernel.org Subject: Re: [PATCH 05/11] rcu/nocb: Make rcu_core() callbacks acceleration (de-)offloading safe In-Reply-To: <20210929221012.228270-6-frederic@kernel.org> References: <20210929221012.228270-1-frederic@kernel.org> <20210929221012.228270-6-frederic@kernel.org> Date: Fri, 01 Oct 2021 18:50:39 +0100 Message-ID: <87a6jsmy6o.mognet@arm.com> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 30/09/21 00:10, Frederic Weisbecker wrote: > When callbacks are offloaded, the NOCB kthreads handle the callbacks > progression on behalf of rcu_core(). > > However during the (de-)offloading process, the kthread may not be > entirely up to the task. As a result some callbacks grace period > sequence number may remain stale for a while because rcu_core() won't > take care of them either. > But that should be taken care of at the tail end of the (de)offloading process, either by rcu_core() or by the NOCB kthreads, no? Or is it e.g. in the case of offloading, we want to make sure an rcu_core() invocation runs callback acceleration because even if the NOCB GP/CB kthreads are being set up, we're not guaranteed is going to do that straight away? IIUC it would be a similar case for deoffload when we stash the NOCB GP/CB kthreads and get rcu_core() running concurrently. > Fix this with forcing callbacks acceleration from rcu_core() as long > as the offloading process isn't complete. >