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 16ED0C433E1 for ; Tue, 26 May 2020 15:45:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DF27A2086A for ; Tue, 26 May 2020 15:45:31 +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 S1728492AbgEZPpZ (ORCPT ); Tue, 26 May 2020 11:45:25 -0400 Received: from us-smtp-2.mimecast.com ([205.139.110.61]:23636 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1728201AbgEZPpY (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-wr1-f70.google.com (mail-wr1-f70.google.com [209.85.221.70]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-330-sPA2QOaTPLOkRSk93i4cvw-1; Tue, 26 May 2020 11:45:20 -0400 X-MC-Unique: sPA2QOaTPLOkRSk93i4cvw-1 Received: by mail-wr1-f70.google.com with SMTP id j8so3203243wrb.9 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=BtNgBSVVQ57W2+T9pfQDI2HDIuMdWMOVPGHbYxMRjMOM3bP2OmpugxfkUc9HEDojg8 Eb4kEKntypRbM+3duQ5I5KApRhivhTuEHUdwfY9Knjtn/oVWOsqtl9w7BX3z9ZNeysir qXE9WVOVtr7bH7TFi5QwttaJ7ol9m+ODrB/mQV+olB6CIids9x0mE5LhPI9tAG0xSrNI ITcmEiVc6TMbZigHtl0DohPhX7b751YNpDN3sdehOWY6OCiQYosysjAJ/E4Mnd1jm/R2 g4OeGl3rY0qK1akHuxvFLmfwlHPqXBbVYv/5Bx5TqJ7Im38gbrvYSss9v9iIyR73Kdmu 0Fpg== X-Gm-Message-State: AOAM531YnwlAxfzWodWrw+BqZRFsVg4AHCrLgyPAD7mfoeeNCbV2tloY HieqNbBlDY2PYNTvQ7me2VqCyd0HpY/aZNVFY82/sKzBWOKNa/qfsBf6Zhl+tC0dLU+9895qDCk e+L3yA2du24ulZoRCd8SnBA== X-Received: by 2002:a05:6000:1202:: with SMTP id e2mr2590856wrx.231.1590507919724; 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-mips-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-mips@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