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 Received: from ws5-mx01.kavi.com (ws5-mx01.kavi.com [34.193.7.191]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 0F1BFEB64DA for ; Wed, 28 Jun 2023 10:48:13 +0000 (UTC) Received: from lists.oasis-open.org (oasis.ws5.connectedcommunity.org [10.110.1.242]) by ws5-mx01.kavi.com (Postfix) with ESMTP id 6F08D12D8A8 for ; Wed, 28 Jun 2023 10:48:12 +0000 (UTC) Received: from lists.oasis-open.org (oasis-open.org [10.110.1.242]) by lists.oasis-open.org (Postfix) with ESMTP id 6AD159865CA for ; Wed, 28 Jun 2023 10:48:12 +0000 (UTC) Received: from host09.ws5.connectedcommunity.org (host09.ws5.connectedcommunity.org [10.110.1.97]) by lists.oasis-open.org (Postfix) with QMQP id 5F38898656F; Wed, 28 Jun 2023 10:48:12 +0000 (UTC) Mailing-List: contact virtio-dev-help@lists.oasis-open.org; run by ezmlm List-ID: Sender: Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: Received: from lists.oasis-open.org (oasis-open.org [10.110.1.242]) by lists.oasis-open.org (Postfix) with ESMTP id 4DAAA98656E for ; Wed, 28 Jun 2023 10:48:10 +0000 (UTC) X-Virus-Scanned: amavisd-new at kavi.com X-MC-Unique: Pwx2U61ZNgqv3QWT1Ugmrg-1 X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1687949284; x=1690541284; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=SVxinU5f7dlDhe327Sb9bJFETxerMLKi0MYEXgxQWng=; b=gkai+fjpBX279yRrM1vvMHDot5D1k+ip3WWvn1XAUF78hkqWgUjAm+MAHGq8Hir8a+ Ds53bMsZ83trAy4RlfEFocuznkcIXFiouacIX5DsruCL2ZJc6iu/FqbWnQVX/ZlL63Vs wQhiyINckDOHYp47vqT8kG6dPhg76CUB6+oZfNvQ/PDbdtyHp+RXt6ZzGu0L83g1g6hN 8VGrZn0GolRriww15dtGzUTezOUochUV9lGJpZBRbPC7hFhzYyIqtibVMryt8bMJNsuf lj2Azh1lht2F8NamEPtCkxWkFOBDd2NKfKYUnGJZX7K7zgXeDboQ7yF9gXKt3GHeV9/T kogQ== X-Gm-Message-State: AC+VfDxrfUGay3Agj6oqBh0Xc1K6sNgG2I52MJtqqr5PstAlIS5v9Xop bRNsQUbuBZxSgSrV2nGkc07MRzFgNzklWfOknH1r9rm+Am6dMqy+dYbSGXqrp2c2WbShsxg1A9K mq0KvGsX/kZiwf0rqNIB7xl0CZCYn X-Received: by 2002:a7b:c7d8:0:b0:3fa:935e:e185 with SMTP id z24-20020a7bc7d8000000b003fa935ee185mr11181510wmk.22.1687949284514; Wed, 28 Jun 2023 03:48:04 -0700 (PDT) X-Google-Smtp-Source: ACHHUZ7dmNCWj9wdsmbEhmxG64LQaiP37Eh///9ClSfeYAUTL+IVfHWRq6vXVq2kx2a6kzey4XnRPg== X-Received: by 2002:a7b:c7d8:0:b0:3fa:935e:e185 with SMTP id z24-20020a7bc7d8000000b003fa935ee185mr11181490wmk.22.1687949284207; Wed, 28 Jun 2023 03:48:04 -0700 (PDT) Date: Wed, 28 Jun 2023 06:47:59 -0400 From: "Michael S. Tsirkin" To: Parav Pandit Cc: Heng Qi , "virtio-comment@lists.oasis-open.org" , "virtio-dev@lists.oasis-open.org" , Jason Wang , Yuri Benditovich , Xuan Zhuo , Cornelia Huck Message-ID: <20230628064137-mutt-send-email-mst@kernel.org> References: <20230622130359-mutt-send-email-mst@kernel.org> <20230622132837-mutt-send-email-mst@kernel.org> <20230622140412-mutt-send-email-mst@kernel.org> <20230622143626-mutt-send-email-mst@kernel.org> <20230622145052-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Subject: [virtio-dev] Re: [virtio-comment] Re: [virtio-dev] Re: [virtio-comment] Re: [PATCH v18] virtio-net: support inner header hash On Thu, Jun 22, 2023 at 08:27:48PM +0000, Parav Pandit wrote: > > > > From: Michael S. Tsirkin > > Sent: Thursday, June 22, 2023 3:02 PM > > > > > Existing fields used by existing drivers must be in MMIO. > > > Device does not have a choice. > > > > They can if they like mask some less important features reducing the footprint. > How do to that? How would device know to not have existing fields on MMIO? As you said yourself, feature bits also have cost. They must be accessed with DMA too, not through MMIO. This set of features can have more bits than the one in MMIO. > > This will be the cost/benefit analysis each vendor does separately. > > > > Case in point, if inner hash support is in 1.3, and linux drivers don't really use > > that at all for a year or two because it's only used by alibaba in their stack, and > > by the time linux starts using them it also supports the new commands, then > > practically devices do not care and can just mask the feature bit in MMIO. > > > Once it lands to config space, it becomes existing fields. What's in which version of the spec is immaterial. If all guests using it also support config space through DMA then it does not matter that technically there was a spec version which had inner hash but not DMA. > More below. > > > > > > > If they want to cut at 1.3 time, they can, but they also can cut it > > > > at 1.2 time, this means some features will not be accessible through > > > > MMIO only through the new commands. > > > > > > > New commands services new fields by newer driver. > > > Newer driver can call new command to get new and old fields both. > > > > yes. > > > > > So 1.3 and 1.4 devices cannot optimize for older drivers. > > > > > > I don't know what this means. > > > I guess next below question answers it. I still don't know what did you mean by "So 1.3 and 1.4 devices cannot optimize for older drivers". If it's immaterial, fine. -- MST --------------------------------------------------------------------- To unsubscribe, e-mail: virtio-dev-unsubscribe@lists.oasis-open.org For additional commands, e-mail: virtio-dev-help@lists.oasis-open.org