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=-4.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,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 31F2CC433E7 for ; Sun, 18 Oct 2020 18:26:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DE9472225A for ; Sun, 18 Oct 2020 18:26:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603045616; bh=SlZgxGNGsrjH8Ef0LjyB2AeicMtrdksOpK9vWtOJZkY=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=BJILUklyQln+dnZq2/xcbAml5Mm6B5xyJ9uZOZ9zN2qeYYnyhVyniVNkv2U/p3z3u hmM9Srr2609hC/44dHMQzwDVSa645+JjtgnCXh7ebWO8AqsuqldnHPTqMVKlOaB5jX reyp0HJ2uSzv+MEiBFyII2reUxor9BQ9Pt6m33aM= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727281AbgJRS0z (ORCPT ); Sun, 18 Oct 2020 14:26:55 -0400 Received: from mail.kernel.org ([198.145.29.99]:42844 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727094AbgJRS0z (ORCPT ); Sun, 18 Oct 2020 14:26:55 -0400 Received: from kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com (unknown [163.114.132.5]) (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 F14AD21655; Sun, 18 Oct 2020 18:26:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603045615; bh=SlZgxGNGsrjH8Ef0LjyB2AeicMtrdksOpK9vWtOJZkY=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=SrYlgbxAuEKP5KePBYv8aFENO3bvDw2e2qqtsLX2eEZuUv+jDB7HJATyQQcNRCIfz JpJvnXUeqWoxcOUtXChnLNXSLUbEYKH1VFSFwzek3kUMA8i8ajW8bi6HBPTCEb6cwS kEJqNgZmdFvzhGpPF8S+kBQATSQ8QrlxASVlZYC8= Date: Sun, 18 Oct 2020 11:26:53 -0700 From: Jakub Kicinski To: Andrew Lunn Cc: Vladimir Oltean , netdev@vger.kernel.org, f.fainelli@gmail.com, vivien.didelot@gmail.com, Christian Eggers , Kurt Kanzenbach Subject: Re: [RFC PATCH 01/13] net: dsa: add plumbing for custom netdev statistics Message-ID: <20201018112653.21735d08@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> In-Reply-To: <20201018173649.GF456889@lunn.ch> References: <20201017213611.2557565-1-vladimir.oltean@nxp.com> <20201017213611.2557565-2-vladimir.oltean@nxp.com> <20201018094951.0016f208@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> <20201018173649.GF456889@lunn.ch> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Sun, 18 Oct 2020 19:36:49 +0200 Andrew Lunn wrote: > On Sun, Oct 18, 2020 at 09:49:51AM -0700, Jakub Kicinski wrote: > > > + struct u64_stats_sync syncp; > > > +} __aligned(1 * sizeof(u64)); > > > > Why aligned to u64? Compiler should pick a reasonable alignment here > > by itself. > > Hi Jakub > > I wondered that as well. But: > > struct gnet_stats_basic_cpu { > struct gnet_stats_basic_packed bstats; > struct u64_stats_sync syncp; > } __aligned(2 * sizeof(u64)); > > /* often modified stats are per-CPU, other are shared (netdev->stats) */ > struct pcpu_sw_netstats { > u64 rx_packets; > u64 rx_bytes; > u64 tx_packets; > u64 tx_bytes; > struct u64_stats_sync syncp; > } __aligned(4 * sizeof(u64)); > > struct pcpu_lstats { > u64_stats_t packets; > u64_stats_t bytes; > struct u64_stats_sync syncp; > } __aligned(2 * sizeof(u64)); > > Cargo cult or is there a real need? Hm, looks like the intent is to enforce power of two alignment to prevent the structure from spanning cache lines. Doesn't make any difference for 1 counter, but I guess we can keep the style for consistency.