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=-2.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 7374FC433E0 for ; Tue, 26 May 2020 15:45:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 51D4420663 for ; Tue, 26 May 2020 15:45:25 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="MuDE1EeN" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729631AbgEZPpZ (ORCPT ); Tue, 26 May 2020 11:45:25 -0400 Received: from us-smtp-1.mimecast.com ([205.139.110.61]:37046 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1728492AbgEZPpY (ORCPT ); Tue, 26 May 2020 11:45:24 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1590507922; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Dt6LQHnd8XQKjoczzuKu5+J73yx/PTFTJmXrE029Qj0=; b=MuDE1EeNGCQ7ZtyasjHIeRquVoyGlw4ms/cF48n+wazvpvZJXtfMaHWohfbEpb6eu/b5pd cagcXwYz82p5Nr22SwvYHKapCY9bDujsdyxeL5jbNE0kD6wB2awofKGhTvYwW4Qc8IF3qm sR+IEuKfj/j1E+CuQh5LmGbRLqBM3+E= Received: from mail-wm1-f72.google.com (mail-wm1-f72.google.com [209.85.128.72]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-330-xwVuuuiFMJGyt-ByE5kj-w-1; Tue, 26 May 2020 11:45:20 -0400 X-MC-Unique: xwVuuuiFMJGyt-ByE5kj-w-1 Received: by mail-wm1-f72.google.com with SMTP id o8so147475wmd.0 for ; Tue, 26 May 2020 08:45:20 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=Dt6LQHnd8XQKjoczzuKu5+J73yx/PTFTJmXrE029Qj0=; b=pSpSQ6Pnax6FgyINJWuzMrvlXOLj+njFbtnccIyvjkD6YkOX8IKFoqeoZInFv1y1zm clIl15aLVJd4rRcqRhXTcNigPC6L4iC+01O0zPeUhL/R+pkPwJkUn08IGL4dcRZ8mrLv HdRZaVXq+W4iLSbSRHGkN+4wd4Gk5k+ayxTI/Wk9/RqR7XZOLkgVds8Yl6MZQA0Uk/zH oV/8OtYwUcD7V4taInjnybQvK2qgw4bLs7pWzZHKck/36R1MbadUE/h7DQtF1ta25aCl EJSgU1upPyyntQnMIXnR14ryB5d+XMjj/3gzmX66t+opCxZk33wbUv+ImTGAr+E6PsYl XbZA== X-Gm-Message-State: AOAM531U9xDogiZz74frHD/z7Z8ZGM3LkZmleKLJUFPDhFYh+cb5xx1a 4LkvSDq8PZ3EIEfNdZil+UEdOhAKsRWzZqeS7BRnkZToswvsAy7YXV/OBe+czjpeJ0ZGN0paHxM Sbp8tDr69iG1LlFUHzUQz X-Received: by 2002:a05:6000:1202:: with SMTP id e2mr2590861wrx.231.1590507919725; Tue, 26 May 2020 08:45:19 -0700 (PDT) X-Google-Smtp-Source: ABdhPJw5If1uNgTKWEisUAJowYTPwcuzMOOow4nahat1ESbDjPkHGjhZwTTbQrIPi02UQ5LtAAq4hw== X-Received: by 2002:a05:6000:1202:: with SMTP id e2mr2590848wrx.231.1590507919516; Tue, 26 May 2020 08:45:19 -0700 (PDT) Received: from localhost.localdomain ([194.230.155.118]) by smtp.gmail.com with ESMTPSA id u10sm32544wmc.31.2020.05.26.08.45.17 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 26 May 2020 08:45:18 -0700 (PDT) Subject: Re: [PATCH v3 7/7] [not for merge] netstats: example use of stats_fs API To: Andrew Lunn Cc: kvm@vger.kernel.org, Christian Borntraeger , Paolo Bonzini , Jim Mattson , Alexander Viro , Emanuele Giuseppe Esposito , David Rientjes , Jonathan Adams , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mips@vger.kernel.org, kvm-ppc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-fsdevel@vger.kernel.org, netdev@vger.kernel.org References: <20200526110318.69006-1-eesposit@redhat.com> <20200526110318.69006-8-eesposit@redhat.com> <20200526141605.GJ768009@lunn.ch> From: Emanuele Giuseppe Esposito Message-ID: <99217496-929f-ed3b-8e9e-bbd26d06e234@redhat.com> Date: Tue, 26 May 2020 17:45:17 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 MIME-Version: 1.0 In-Reply-To: <20200526141605.GJ768009@lunn.ch> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org Hi Andrew > How do you atomically get and display a group of statistics? > > If you look at how the netlink socket works, you will see code like: > > do { > start = u64_stats_fetch_begin_irq(&cpu_stats->syncp); > rx_packets = cpu_stats->rx_packets; > rx_bytes = cpu_stats->rx_bytes; > .... > } while (u64_stats_fetch_retry_irq(&cpu_stats->syncp, start)); > > It will ensure that rx_packets and rx_bytes are consistent with each > other. If the value of the sequence counter changes while inside the > loop, the loop so repeated until it does not change. > > In general, hardware counters in NICs are the same. You tell it to > take a snapshot of the statistics counters, and then read them all > back, to give a consistent view across all the statistics. > > I've not looked at this new code in detail, but it looks like you have > one file per statistic, and assume each statistic is independent of > every other statistic. This independence can limit how you use the > values, particularly when debugging. The netlink interface we use does > not have this limitation. You're right, statistics are treated independently so what you describe is currently not supported. In KVM the utilization is more qualitative, so there isn't such problem. But as long as the interface is based on file access, the possibility of snapshotting might not be useful; however, it could still be considered to be added later together with the binary access. Jonathan, how is your metricfs handling this case? Thank you, Emanuele