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=-5.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham 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 837F4C2BA83 for ; Thu, 13 Feb 2020 08:30:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 503D121734 for ; Thu, 13 Feb 2020 08:30:13 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="HdWCTIPh" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729584AbgBMIaM (ORCPT ); Thu, 13 Feb 2020 03:30:12 -0500 Received: from bombadil.infradead.org ([198.137.202.133]:47938 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726232AbgBMIaM (ORCPT ); Thu, 13 Feb 2020 03:30:12 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.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=lqYHniyuFF82g1hkULXfEHjo4HV1jpimDv0o2K20OUU=; b=HdWCTIPhz1Qqup3ZyZCHR7FwoA zWEfEKNgo3x7t8+smFyp0QXWcoE+WJVmBNcjK45jVIeqVVXG0n8eOwFoHSA8kaRhR4zbSM9usP1JC JXvNuUCtU2SddqMInPipINGFrrpqD/a/0yOEGrbFa9f21KFd6dK7qZABfYm6g/2oiX/wlnz0dC5Or qzHXAAuIq0Zmql9FTORDSbQlXabm4Cbqka71D5FyVxdbw1HrMSnpdlvFco3V6fjRLnTrwZKmf7Ff3 r1IlfGsVZPnfBZYSmFmm/Zgv1FmELK9TvsI0Sd/yLAbgZH8OkVxmBBDCAZVC/4GXMiRxU2RzQuN9U XN+kZHhg==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1j29sf-0003Jc-71; Thu, 13 Feb 2020 08:29:53 +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 18D2C300606; Thu, 13 Feb 2020 09:28:02 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id A01072B4CEBC2; Thu, 13 Feb 2020 09:29:51 +0100 (CET) Date: Thu, 13 Feb 2020 09:29:51 +0100 From: Peter Zijlstra To: Joel Fernandes Cc: linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, rostedt@goodmis.org, mingo@kernel.org, gregkh@linuxfoundation.org, gustavo@embeddedor.com, tglx@linutronix.de, paulmck@kernel.org, josh@joshtriplett.org, mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com, "Steven Rostedt (VMware)" Subject: Re: [PATCH v2 6/9] perf,tracing: Prepare the perf-trace interface for RCU changes Message-ID: <20200213082951.GK14897@hirez.programming.kicks-ass.net> References: <20200212210139.382424693@infradead.org> <20200212210750.142334759@infradead.org> <20200212232830.GB170680@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200212232830.GB170680@google.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 12, 2020 at 06:28:30PM -0500, Joel Fernandes wrote: > On Wed, Feb 12, 2020 at 10:01:45PM +0100, Peter Zijlstra wrote: > > The tracepoint interface will stop providing regular RCU context; make > > sure we do it ourselves, since perf makes use of regular RCU protected > > data. > > > > Suggested-by: Steven Rostedt (VMware) > > Suggested-by: Mathieu Desnoyers > > Signed-off-by: Peter Zijlstra (Intel) > > --- > > kernel/events/core.c | 5 +++++ > > 1 file changed, 5 insertions(+) > > > > --- a/kernel/events/core.c > > +++ b/kernel/events/core.c > > @@ -8950,6 +8950,7 @@ void perf_tp_event(u16 event_type, u64 c > > { > > struct perf_sample_data data; > > struct perf_event *event; > > + unsigned long rcu_flags; > > The flags are not needed I guess, if you agree on not using in_nmi() in > trace_rcu_enter(). Even then we need to store the state: 'didn't do nothing' vs 'did call rcu_needs_to_wake_up_and_pay_attention_noaw'. That is, we only need to do something (expensive!) when !rcu_is_watching().