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 B9E1CC2D0C2 for ; Fri, 3 Jan 2020 16:36:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8B2F621835 for ; Fri, 3 Jan 2020 16:36:10 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=ziepe.ca header.i=@ziepe.ca header.b="Eruve59U" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728197AbgACQgJ (ORCPT ); Fri, 3 Jan 2020 11:36:09 -0500 Received: from mail-qk1-f196.google.com ([209.85.222.196]:34163 "EHLO mail-qk1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728190AbgACQgI (ORCPT ); Fri, 3 Jan 2020 11:36:08 -0500 Received: by mail-qk1-f196.google.com with SMTP id j9so34586631qkk.1 for ; Fri, 03 Jan 2020 08:36:07 -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:in-reply-to:user-agent; bh=sudCo7UPl2UlykD1ORZaeISXEUoxyJkiMctvtW517Vk=; b=Eruve59U1yI6zP+DxqzqA6nOcfTxBDD2pvh1trBTe+FIfzgwQKQt9nZ8gEpOeV9C6G ySUQVUr5F8gO7fcUqlyy/1o6PYcXuY3aO/le+gaPWnBy66Z4b09Vn7D6UdkPPGK0X1RO 6vqFyrIhzRPZwieZHcCenPPyNRl2nDxm+8kXc+E/euj9D+Q6miZAXaDedlXU+FKeI26s FeuTtRlYbmQ5LUs/L6btIPvJXQTNy0XrRcjvo9vIp8b4uuFuUtX2FnRKGP8+B0tvRfYS 31+QXO7LmHL7CGOXDFpFuemQa6G90fpxFrmFnAn+3T+dxIABrpCXux5MrFKGirJTkppv Pk3A== 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:in-reply-to:user-agent; bh=sudCo7UPl2UlykD1ORZaeISXEUoxyJkiMctvtW517Vk=; b=Gva01e0wK6JZRVTJZovb3JhTk2JkGyEr2+p3Fu2Fa6S0k6rLQTDY85pCoUDBjWvrTb dI3uldQ3dHUcVm/zo0qmfNoBn7xmdF83oncGbe3a5fQAKe6T5WZ98o/hSLy2I+vXWdEd aYDbvs+rjsyAQjTlt522rZvKPgIfCYP7DUJxI4qUI2qrTvuUTPBuGysOSl6ubmTItxYH IdPUNgqwurSnHRle/fWGVRHx2tfhnO/BDhlbAGu43MwQQ6rMV4tFE6hiFZqm8K5pFL8C a8T/GLaF6fkDozczMzc9zsEfq6N6QLASOSz6Oo5G2pZmSA8n7kIrc8Tx7FNzX3aPWohZ wg7g== X-Gm-Message-State: APjAAAUxOs4V5KCeaUr3fARLJKc0FJghQeR8hgAOSlItnUKhRg+1fH7+ O2wqcEhk4hiuvz11w3Ebcc4gjQ== X-Google-Smtp-Source: APXvYqzXPuO8Q2iCwT4AOJu6PVHWbP/PHxoj1vucsu2b26srgGmPlSmUUaaGVFAEw5nH5VrXrOROLg== X-Received: by 2002:a37:a807:: with SMTP id r7mr63400124qke.346.1578069367426; Fri, 03 Jan 2020 08:36:07 -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 a36sm18738401qtk.29.2020.01.03.08.36.06 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Fri, 03 Jan 2020 08:36:06 -0800 (PST) Received: from jgg by mlx.ziepe.ca with local (Exim 4.90_1) (envelope-from ) id 1inPvi-0001M8-Gt; Fri, 03 Jan 2020 12:36:06 -0400 Date: Fri, 3 Jan 2020 12:36:06 -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: <20200103163606.GC9706@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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 06:31:18PM +0200, Liran Alon wrote: > > I am surprised that AMD is different here, the evolution of the WC > > feature on x86 was to transparently speed up graphics, so I'm pretty > > surprised AMD can get away with not ordering the same as Intel.. > > Completely agree. I was very surprised to see this from AMD SDM and > Optimization Guide SDM. It made sense to me too that graphics frame > buffer is written to WC memory and then is committed to GPU by > writing to some doorbell register mapped as UC memory. It is possible this manual is wrong or misleading? Having WC writes not strongly order after UC writes to the same device, on x86, seems very, very surprising to me. Everything is ordered on x86 :) Jason