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 277C3C433EF for ; Wed, 9 Mar 2022 01:19:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230438AbiCIBUN (ORCPT ); Tue, 8 Mar 2022 20:20:13 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34626 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230507AbiCIBT5 (ORCPT ); Tue, 8 Mar 2022 20:19:57 -0500 Received: from desiato.infradead.org (desiato.infradead.org [IPv6:2001:8b0:10b:1:d65d:64ff:fe57:4e05]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6BF5D30A for ; Tue, 8 Mar 2022 17:12:03 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=XqYDQ0sO8lLcFH38iNpLV9+za02YSz1bbsT0KsfeIP8=; b=Pjh/y28/PAdf3s2neTwwwFdFwP q2hbcI7URxbuj/rRtMJv+J+/zMaLs1xfegdV5hwwbn1TReO6VUZYFQnesEN9d+VS0DOtvRupX2AFL /mUpbgjG/CCa7zHYIUoIzvf8WvNFHOqK1IZwm9Di9sCZeI0Lm4LS+hVkMc2BvMzeIGDVh/UahgjdK XIoO1f3XX9cgSrxPjX1Flc9HQNbdxAWjNZ//HopeZIxaOmZdaxNOpObW2kc49+SOEWA7BEKrXyQIa NF+qhPF3PZU0H16aajB15UWjkI8Sr3HbdSJ+y1e8cUydVc42gBfRxZXIRbCHDaX/Cvi8OTKS226+A xqE1CzsQ==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1nRjJc-00GaWd-EZ; Tue, 08 Mar 2022 23:32:28 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 149C030027B; Wed, 9 Mar 2022 00:32:25 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id AE5D0203C81E0; Wed, 9 Mar 2022 00:32:25 +0100 (CET) Date: Wed, 9 Mar 2022 00:32:25 +0100 From: Peter Zijlstra To: Marek Szyprowski Cc: Chengming Zhou , mingo@redhat.com, vincent.guittot@linaro.org, bristot@redhat.com, zhaolei@cn.fujitsu.com, tj@kernel.org, lizefan.x@bytedance.com, hannes@cmpxchg.org, linux-kernel@vger.kernel.org, Paul McKenney Subject: Re: [PATCH v3 2/3] sched/cpuacct: optimize away RCU read lock Message-ID: References: <20220220051426.5274-1-zhouchengming@bytedance.com> <20220220051426.5274-2-zhouchengming@bytedance.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Mar 09, 2022 at 12:20:33AM +0100, Marek Szyprowski wrote: > On 20.02.2022 06:14, Chengming Zhou wrote: > > Since cpuacct_charge() is called from the scheduler update_curr(), > > we must already have rq lock held, then the RCU read lock can > > be optimized away. > > > > And do the same thing in it's wrapper cgroup_account_cputime(), > > but we can't use lockdep_assert_rq_held() there, which defined > > in kernel/sched/sched.h. > > > > Suggested-by: Peter Zijlstra (Intel) > > Signed-off-by: Chengming Zhou > > This patch landed recently in linux-next as commit dc6e0818bc9a > ("sched/cpuacct: Optimize away RCU read lock"). On my test systems I > found that it triggers a following warning in the early boot stage: > > Calibrating delay loop (skipped), value calculated using timer > frequency.. 48.00 BogoMIPS (lpj=240000) > pid_max: default: 32768 minimum: 301 > Mount-cache hash table entries: 2048 (order: 1, 8192 bytes, linear) > Mountpoint-cache hash table entries: 2048 (order: 1, 8192 bytes, linear) > CPU: Testing write buffer coherency: ok > CPU0: Spectre v2: using BPIALL workaround > > ============================= > WARNING: suspicious RCU usage > 5.17.0-rc5-00050-gdc6e0818bc9a #11458 Not tainted > ----------------------------- > ./include/linux/cgroup.h:481 suspicious rcu_dereference_check() usage! Arguably, with the flavours folded again, rcu_dereference_check() ought to default include rcu_read_lock_sched_held() or its equivalent I suppose. Paul?