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 C4A8AC433F5 for ; Fri, 4 Mar 2022 14:29:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239817AbiCDO3w (ORCPT ); Fri, 4 Mar 2022 09:29:52 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42086 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239789AbiCDO3q (ORCPT ); Fri, 4 Mar 2022 09:29:46 -0500 Received: from gateway33.websitewelcome.com (gateway33.websitewelcome.com [192.185.145.216]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B116B1B60BA for ; Fri, 4 Mar 2022 06:28:58 -0800 (PST) Received: from cm16.websitewelcome.com (cm16.websitewelcome.com [100.42.49.19]) by gateway33.websitewelcome.com (Postfix) with ESMTP id 125DA501C for ; Fri, 4 Mar 2022 08:28:58 -0600 (CST) Received: from gator4132.hostgator.com ([192.185.4.144]) by cmsmtp with SMTP id Q8vRnY7eyXvvJQ8vSn23vL; Fri, 04 Mar 2022 08:28:58 -0600 X-Authority-Reason: nr=8 Received: from host-82-63-1-3.business.telecomitalia.it ([82.63.1.3]:40132 helo=[10.0.0.45]) by gator4132.hostgator.com with esmtpsa (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 (Exim 4.94.2) (envelope-from ) id 1nQ8vR-0046yN-AP; Fri, 04 Mar 2022 08:28:57 -0600 Message-ID: <78d798aa-388c-70bc-4227-985ba76c1d7e@kernel.org> Date: Fri, 4 Mar 2022 15:28:54 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.5.0 Subject: Re: [PATCH] tracing/osnoise: Force quiescent states while tracing Content-Language: en-US To: Nicolas Saenz Julienne Cc: mingo@redhat.com, linux-kernel@vger.kernel.org, mtosatti@redhat.com, paulmck@kernel.org, rostedt@goodmis.org References: <20220228141423.259691-1-nsaenzju@redhat.com> From: Daniel Bristot de Oliveira In-Reply-To: <20220228141423.259691-1-nsaenzju@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - gator4132.hostgator.com X-AntiAbuse: Original Domain - vger.kernel.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - kernel.org X-BWhitelist: no X-Source-IP: 82.63.1.3 X-Source-L: No X-Exim-ID: 1nQ8vR-0046yN-AP X-Source: X-Source-Args: X-Source-Dir: X-Source-Sender: host-82-63-1-3.business.telecomitalia.it ([10.0.0.45]) [82.63.1.3]:40132 X-Source-Auth: kernel@bristot.me X-Email-Count: 4 X-Source-Cap: YnJpc3RvdG1lO2JyaXN0b3RtZTtnYXRvcjQxMzIuaG9zdGdhdG9yLmNvbQ== X-Local-Domain: no Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2/28/22 15:14, Nicolas Saenz Julienne wrote: > At the moment running osnoise on an isolated CPU and a PREEMPT_RCU > kernel might have the side effect of extending grace periods too much. > This will eventually entice RCU to schedule a task on the isolated CPU > to end the overly extended grace period, adding unwarranted noise to the > CPU being traced in the process. > > So, check if we're the only ones running on this isolated CPU and that > we're on a PREEMPT_RCU setup. If so, let's force quiescent states in > between measurements. > > Non-PREEMPT_RCU setups don't need to worry about this as osnoise main > loop's cond_resched() will go though a quiescent state for them. > > Note that this same exact problem is what extended quiescent states were > created for. But adapting them to this specific use-case isn't trivial > as it'll imply reworking entry/exit and dynticks/context tracking code. Hey Nicolas, While testing this patch with rtla osnoise on the 5.17.0-rc6-rt10+, when I hit ^c on osnoise top, the system freezes :-/. Could you try that on your system? -- Daniel