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 C66A1C433FE for ; Wed, 11 May 2022 14:30:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241039AbiEKOaF (ORCPT ); Wed, 11 May 2022 10:30:05 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43796 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237191AbiEKOaC (ORCPT ); Wed, 11 May 2022 10:30:02 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id EF2D8106A69; Wed, 11 May 2022 07:30:00 -0700 (PDT) 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 dfw.source.kernel.org (Postfix) with ESMTPS id 92E166101F; Wed, 11 May 2022 14:30:00 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id E59E8C34113; Wed, 11 May 2022 14:29:58 +0000 (UTC) Date: Wed, 11 May 2022 10:29:57 -0400 From: Steven Rostedt To: Uladzislau Rezki Cc: "Paul E. McKenney" , Joel Fernandes , Alison Chaiken , Sebastian Andrzej Siewior , LKML , RCU , Frederic Weisbecker , Neeraj Upadhyay , Oleksiy Avramchenko Subject: Re: [PATCH] rcu/nocb: Add an option to ON/OFF an offloading from RT context Message-ID: <20220511102957.56bd582b@gandalf.local.home> In-Reply-To: References: <20220507223247.GK1790663@paulmck-ThinkPad-P17-Gen-1> <20220508213222.GL1790663@paulmck-ThinkPad-P17-Gen-1> <20220509033740.GM1790663@paulmck-ThinkPad-P17-Gen-1> <20220509181417.GO1790663@paulmck-ThinkPad-P17-Gen-1> <20220510100135.62a4f7df@gandalf.local.home> X-Mailer: Claws Mail 3.17.8 (GTK+ 2.24.33; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 11 May 2022 15:39:56 +0200 Uladzislau Rezki wrote: > > rcuop/6-54 [000] .N.. 183.753018: rcu_invoke_callback: rcu_preempt rhp=0xffffff88ffd440b0 func=__d_free.cfi_jt > rcuop/6-54 [000] .N.. 183.753020: rcu_invoke_callback: rcu_preempt rhp=0xffffff892ffd8400 func=inode_free_by_rcu.cfi_jt > rcuop/6-54 [000] .N.. 183.753021: rcu_invoke_callback: rcu_preempt rhp=0xffffff89327cd708 func=i_callback.cfi_jt > ... > rcuop/6-54 [000] .N.. 183.755941: rcu_invoke_callback: rcu_preempt rhp=0xffffff8993c5a968 func=i_callback.cfi_jt > rcuop/6-54 [000] .N.. 183.755942: rcu_invoke_callback: rcu_preempt rhp=0xffffff8993c4bd20 func=__d_free.cfi_jt > rcuop/6-54 [000] dN.. 183.755944: rcu_batch_end: rcu_preempt CBs-invoked=2112 idle=>c<>c<>c<>c< > rcuop/6-54 [000] dN.. 183.755946: rcu_utilization: Start context switch > rcuop/6-54 [000] dN.. 183.755946: rcu_utilization: End context switch > > > i spent some time in order to understand why the context was not switched, > even though the "rcuop" kthread was marked as TIF_NEED_RESCHED and an IPI > was sent to the CPU_0 to reschedule. The last "." in latency field shows > that a context has not disabled any preemption. So everything should be fine. > > An explanation is that a local_bh_disable() modifies the current_thread_info()->preempt.count > so a task becomes non preemtable but the ftrace does not provide any signal about > it. So i was fooled for some time by my tracer logs. > > Do you have any thoughts about it? Should it be solved or signaled > somehow that a task in fact is not preemtable if a counter > 0? Hmm, it should show it in the first part (where the 'd' is). Is this a snapshot from the kernel or from trace-cmd? -- Steve