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 X-Spam-Level: X-Spam-Status: No, score=-3.9 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2C410C5517A for ; Mon, 26 Oct 2020 08:45:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9B60022400 for ; Mon, 26 Oct 2020 08:45:52 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="b2Jg5WME" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1772056AbgJZIpv (ORCPT ); Mon, 26 Oct 2020 04:45:51 -0400 Received: from merlin.infradead.org ([205.233.59.134]:46928 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1771224AbgJZIpv (ORCPT ); Mon, 26 Oct 2020 04:45:51 -0400 X-Greylist: delayed 1517 seconds by postgrey-1.27 at vger.kernel.org; Mon, 26 Oct 2020 04:45:51 EDT DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; 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=cG+bUw0htssS2VsM1tSm5/tJVv+7Iw86NvNGo250wAA=; b=b2Jg5WMEQkbZCXLmYMhmlHHGD0 i0wezkUlu8euA7C3i2l6BEyNR+Rvd9yXt2Gi2xU83cNxNkLuIMgdipp7/bU3SQs4dWi1jCAbIu7lM C/wcBsh2JqIVv2iIIFP9QTKo98vhcZnUap3lPxPWCQ0yn2XH8Bb32SuF0hMvpnWguLjEZNa/mmuze Fpl/ZJFgwddm2cJ6/vlI5ZnRRnIOafcwoSdE4NBPojQDX51UGO47kKX23tdMytouXJolVVCkJvq2a UjNGewtz2ZPHOwXqRt2sPujjEOqzwWNNlmWPo3uKGuHVFpIfOrF2/hmIg9rgGDWF0xIdUbVfXf93X fAR5oAWw==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1kWxjh-00070s-OX; Mon, 26 Oct 2020 08:20:13 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 9853A301179; Mon, 26 Oct 2020 09:20:10 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 5E077214ECD42; Mon, 26 Oct 2020 09:20:10 +0100 (CET) Date: Mon, 26 Oct 2020 09:20:10 +0100 From: Peter Zijlstra To: Joel Fernandes Cc: Michael Jeanson , linux-kernel@vger.kernel.org, mathieu.desnoyers@efficios.com, Steven Rostedt , Alexei Starovoitov , Yonghong Song , "Paul E . McKenney" , Ingo Molnar , Arnaldo Carvalho de Melo , Mark Rutland , Alexander Shishkin , Jiri Olsa , Namhyung Kim , bpf@vger.kernel.org Subject: Re: [RFC PATCH 6/6] tracing: use sched-RCU instead of SRCU for rcuidle tracepoints Message-ID: <20201026082010.GC2628@hirez.programming.kicks-ass.net> References: <20201023195352.26269-1-mjeanson@efficios.com> <20201023195352.26269-7-mjeanson@efficios.com> <20201023211359.GC3563800@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201023211359.GC3563800@google.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Oct 23, 2020 at 05:13:59PM -0400, Joel Fernandes wrote: > On Fri, Oct 23, 2020 at 03:53:52PM -0400, Michael Jeanson wrote: > > From: Mathieu Desnoyers > > > > Considering that tracer callbacks expect RCU to be watching (for > > instance, perf uses rcu_read_lock), we need rcuidle tracepoints to issue > > rcu_irq_{enter,exit}_irqson around calls to the callbacks. So there is > > no point in using SRCU anymore given that rcuidle tracepoints need to > > ensure RCU is watching. Therefore, simply use sched-RCU like normal > > tracepoints for rcuidle tracepoints. > > High level question: > > IIRC, doing this increases overhead for general tracing that does not use > perf, for 'rcuidle' tracepoints such as the preempt/irq enable/disable > tracepoints. I remember adding SRCU because of this reason. > > Can the 'rcuidle' information not be pushed down further, such that perf does > it because it requires RCU to be watching, so that it does not effect, say, > trace events? There's very few trace_.*_rcuidle() users left. We should eradicate them and remove the option. It's bugs to begin with.