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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_2 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 CC636C433E0 for ; Fri, 15 May 2020 01:43:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AA64820671 for ; Fri, 15 May 2020 01:43:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728093AbgEOBnx (ORCPT ); Thu, 14 May 2020 21:43:53 -0400 Received: from mail.kernel.org ([198.145.29.99]:50988 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727084AbgEOBnx (ORCPT ); Thu, 14 May 2020 21:43:53 -0400 Received: from oasis.local.home (cpe-66-24-58-225.stny.res.rr.com [66.24.58.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 224802065F; Fri, 15 May 2020 01:43:51 +0000 (UTC) Date: Thu, 14 May 2020 21:43:49 -0400 From: Steven Rostedt To: Thomas Gleixner Cc: LKML , x86@kernel.org, "Paul E. McKenney" , Andy Lutomirski , Alexandre Chartre , Frederic Weisbecker , Paolo Bonzini , Sean Christopherson , Masami Hiramatsu , Petr Mladek , Joel Fernandes , Boris Ostrovsky , Juergen Gross , Brian Gerst , Mathieu Desnoyers , Josh Poimboeuf , Will Deacon , Tom Lendacky , Wei Liu , Michael Kelley , Jason Chen CJ , Zhao Yakui , "Peter Zijlstra (Intel)" Subject: Re: [patch V5 04/38] x86: Make hardware latency tracing explicit Message-ID: <20200514214349.24642172@oasis.local.home> In-Reply-To: <20200512213809.784331304@linutronix.de> References: <20200512210059.056244513@linutronix.de> <20200512213809.784331304@linutronix.de> X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 12 May 2020 23:01:03 +0200 Thomas Gleixner wrote: > --- a/arch/x86/kernel/cpu/mce/core.c > +++ b/arch/x86/kernel/cpu/mce/core.c > @@ -1916,7 +1916,7 @@ static __always_inline void exc_machine_ > mce_check_crashing_cpu()) > return; > > - nmi_enter(); > + nmi_enter_notrace(); Now a machine check exception could happen and be a cause of latency (although there may be more issues if it does). The "nmi_enter trace" version does two things. One is for time measurements (if available), and the other is just letting the hardware latency know it happen (a simple increment). The only thing that is checked is "smp_processor_id()" (I just remembered it doesn't need per cpu, as it only runs on a single CPU at a time). Could the notrace version supply the increment, and leave the trace_clock() in the trace version? -- Steve > /* > * The call targets are marked noinstr, but objtool can't figure > * that out because it's an indirect call. Annotate it. >