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=-3.8 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 5D18CC433DF for ; Fri, 31 Jul 2020 18:05:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3C15F2177B for ; Fri, 31 Jul 2020 18:05:56 +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="G5Unzz6C" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387688AbgGaSFz (ORCPT ); Fri, 31 Jul 2020 14:05:55 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55734 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387676AbgGaSFy (ORCPT ); Fri, 31 Jul 2020 14:05:54 -0400 Received: from merlin.infradead.org (merlin.infradead.org [IPv6:2001:8b0:10b:1231::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 19EC0C061574 for ; Fri, 31 Jul 2020 11:05:52 -0700 (PDT) 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=t1zAWmfo6qZtPbotvLd0epPAf9W0ABBv1rEkWfGnG6M=; b=G5Unzz6CF86b4LiWMq14iFn1a0 k335RypiF19sg+JpP4kuO5gOOvqtUJpqPeXAF8kEDx/AHklbwDoYY20wCwIQjhzEZeQELdFdZmhe+ Q72Xbc933oafaTBi/l6LEonJXabKCu/uTEMwHCCm/RyUq68jWZWSqB4t+UwOEM8SsCIYh94r5MliY Qg9wAXER+eY1aB0ofmrgYCW0WLLhvKRAk9z7sH0g7sJDV1vj7h7XFNYYQZbAbUPqcdjQXt68i3i1W Ui0Zc8Vq9ayh0rnkxON5TOIcyvp+5V0jU9ILXlDkFGS5/JVGoKx8+8GdSyjLuWamiESSFNp1zKri8 wtA8Zmnw==; 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 1k1ZPZ-0001r8-Eg; Fri, 31 Jul 2020 18:05:41 +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 966B33050F0; Fri, 31 Jul 2020 20:05:39 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 64849203C70DC; Fri, 31 Jul 2020 20:05:39 +0200 (CEST) Date: Fri, 31 Jul 2020 20:05:39 +0200 From: peterz@infradead.org To: Andi Kleen Cc: Jiri Olsa , David Ahern , Jiri Olsa , Arnaldo Carvalho de Melo , lkml , Ingo Molnar , Namhyung Kim , Alexander Shishkin , Michael Petlan , Ian Rogers , =?iso-8859-1?Q?Genevi=E8ve?= Bastien , Wang Nan , Jeremie Galarneau Subject: Re: [PATCH 0/6] perf tools: Add wallclock time conversion support Message-ID: <20200731180539.GA2674@hirez.programming.kicks-ass.net> References: <20200730213950.1503773-1-jolsa@kernel.org> <20200730221423.GH2638@hirez.programming.kicks-ass.net> <20200731074726.GA1485940@krava> <20200731153612.GC1299820@tassilo.jf.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200731153612.GC1299820@tassilo.jf.intel.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jul 31, 2020 at 08:36:12AM -0700, Andi Kleen wrote: > > yep, we have a customer that needs to compare data from multiple servers > > It's also needed to correlate over different guests on the same machine. > This is an important use case. Both these cases you want to sync up CLOCK_MONOTONIC, using walltime is just utterly misguided. What happens if the servers have (per accident or otherwise) different DST settings, or someone does a clock_setttime() for giggles. All you really want is a clock that runs at the same rate but is not subject to random jumps and user foibles.