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=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 15C63C32767 for ; Fri, 3 Jan 2020 19:06:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E0B48222C3 for ; Fri, 3 Jan 2020 19:06:42 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=ziepe.ca header.i=@ziepe.ca header.b="dU+uoPDj" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728417AbgACTGm (ORCPT ); Fri, 3 Jan 2020 14:06:42 -0500 Received: from mail-qk1-f196.google.com ([209.85.222.196]:32862 "EHLO mail-qk1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728373AbgACTGl (ORCPT ); Fri, 3 Jan 2020 14:06:41 -0500 Received: by mail-qk1-f196.google.com with SMTP id d71so26713507qkc.0 for ; Fri, 03 Jan 2020 11:06:41 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ziepe.ca; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:content-transfer-encoding:in-reply-to :user-agent; bh=EUhwY4KN3Hi+wm+tnv9ZA4z55nw+ALefY3jU2duuCU0=; b=dU+uoPDjAMvMqUkH3zdKc5lBHfmgslkIvSvgbRSsETucM72+/5AR706J1qxKdWYxMy zrQNoVmazalzmV6BVpgUd0Hdd0FJKlhPMQRV1Kn5zzdLJA+zfxNIKJFj5aBIRGx85ADi AGk+m7Q2s+HIiRNIg6CwF6G8mczWXk+ciquiR2TvkQsub9GM4QVYrLyjoAHooiBBqw6J i5SJkZCc8zhOceaRl9wRJtZl5U9tWLgvPuC6bpurHlDxnE4kVm6SUSpXIJF1dNBM4DBM aou6rih0etSIbAHpsfh1KzBX9IBErIoseIPHl4Lp2inCJHAbakwE39JqKnQ7efFTe6t1 5UkA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:content-transfer-encoding :in-reply-to:user-agent; bh=EUhwY4KN3Hi+wm+tnv9ZA4z55nw+ALefY3jU2duuCU0=; b=MjYdQtMwHDAtI2CayNe3ULazES9kDdoep1ZbFBPdRKy1joFittcxvRRm/2bwSwzN+O tHvKjuooMiMOnJVeRsQ/W87qyVDGpHeql91GAdh5aCCj5q/SI5tV4KxH0VyHE7887RLR KVdzWwnI9SkcL5oK+GL6p3coP6W3j4Wb3L9BEHoF99u5tRxivBf/Di7kSkDhipfH50JX RBPYQYWlEMr2dykY6rwc8ngd6WlEYuwoEDsSBbfzqqBiX7hHuw/kXLCKlaYvdDHWTHoZ /wlr+7ipULsTx8n8sIxEKBc/oeAPN7GO5R05fA7moJ8Gmza8kR0JCdJjDrjmAM3rGMVr SClA== X-Gm-Message-State: APjAAAVTmzFhfcydjJLeosiwp66wUNCHgGcKODOi7ZZkAm8p2QCD7CNA crExNVMgItEtMwD18b4OZPlKNA== X-Google-Smtp-Source: APXvYqz1n8Sh0mx4cCcsQyHa2xl1wQP/5+oQQG13fHDdhdNT2yV1hAnWgJ3cAg2DVYLvj9U3j0xyDQ== X-Received: by 2002:a37:77c5:: with SMTP id s188mr74200680qkc.369.1578078400638; Fri, 03 Jan 2020 11:06:40 -0800 (PST) Received: from ziepe.ca (hlfxns017vw-142-68-57-212.dhcp-dynamic.fibreop.ns.bellaliant.net. [142.68.57.212]) by smtp.gmail.com with ESMTPSA id u4sm16688451qkh.59.2020.01.03.11.06.40 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Fri, 03 Jan 2020 11:06:40 -0800 (PST) Received: from jgg by mlx.ziepe.ca with local (Exim 4.90_1) (envelope-from ) id 1inSHP-0005Qf-J8; Fri, 03 Jan 2020 15:06:39 -0400 Date: Fri, 3 Jan 2020 15:06:39 -0400 From: Jason Gunthorpe To: Liran Alon Cc: Will Deacon , saeedm@mellanox.com, leon@kernel.org, netdev@vger.kernel.org, linux-rdma@vger.kernel.org, eli@mellanox.com, tariqt@mellanox.com, danielm@mellanox.com, =?utf-8?B?SMOla29u?= Bugge Subject: Re: [PATCH] net: mlx5: Use writeX() to ring doorbell and remove reduntant wmb() Message-ID: <20200103190639.GD9706@ziepe.ca> References: <20200102174436.66329-1-liran.alon@oracle.com> <20200102192934.GH9282@ziepe.ca> <6524AE07-2ED7-41B5-B761-9F6BE8D2049B@oracle.com> <20200102205847.GJ9282@ziepe.ca> <79BB7EDF-406D-4FA1-ADDC-634D55F15C37@oracle.com> <20200103133749.GA9706@ziepe.ca> <1C8D5596-F9AD-4E9F-B462-D63DCEEFFE54@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <1C8D5596-F9AD-4E9F-B462-D63DCEEFFE54@oracle.com> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Fri, Jan 03, 2020 at 08:38:51PM +0200, Liran Alon wrote: > Actually after re-reading AMD Optimization Guide SDM, I see it is > guaranteed that: “Write-combining is closed if all 64 bytes of the > write buffer are valid”. And this is indeed always the case for AWS > ENA LLQ. Because as can be seen at ena_com_config_llq_info(), > desc_list_entry_size is either 128, 192 or 256. i.e. Always a > multiple of 64 bytes. So this explains why this wasn’t an issue in > production. That makes a lot of sense So, the problem with defining WC in the kernel memory model still remains, but it is back to a theoretical one. Jason