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 7BEE9C76196 for ; Mon, 3 Apr 2023 15:07:05 +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 D338398FAA for ; Mon, 3 Apr 2023 15:07:04 +0000 (UTC) Received: from lists.oasis-open.org (oasis-open.org [10.110.1.242]) by lists.oasis-open.org (Postfix) with ESMTP id B7A06986400 for ; Mon, 3 Apr 2023 15:07:04 +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 AB0E89863D6; Mon, 3 Apr 2023 15:07:04 +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 9BCC89863DD for ; Mon, 3 Apr 2023 15:07:04 +0000 (UTC) X-Virus-Scanned: amavisd-new at kavi.com X-MC-Unique: 2vjN1G3INpKmCQhmM2U0eA-1 X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; t=1680534414; 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=UhOlvUnZPjx9ar17FWMMNs1oDfbZiA03vaE0YQb5kLs=; b=uPI3Mm7NyxLkfzPX4cBsbevMBfICd+0JjO/VYrautqHmPS3NCmlcVXWvL7UJQziqBx n/epiNFPTTSsEXRqFouzD5mm8hWjAqRmKlKq/WtbLKs1atagDK1kYXiYXCWlytjCFsfl LTx1Wqd4Kkbx7XhBFWhngtVCO4wflMW9N+0fxDlt0ZIHnG18PJP6BLqAvc7y+PXDnqr6 UFcwe1HiOFiO4phji1Kr8f8R6N5xWOwD3tc2yj+yqRldUOI7btj0rFc+XU5QtLKRg+u5 E0Ub/Oeq0a++ir0h70ZkrHBQnP4WW5eZLkKH6BunnkS7m8i0d+D7xSQuNNAnBB5ue9eo RWJQ== X-Gm-Message-State: AAQBX9e4RaBzi0ztV07aQkQIbzZm+OdcivAoxcGXoA/4AsWh4fTUDjNn cOuc3w/KrPTpEaglpCdKsXUVPALHxL9VralnLJPulVvK941tt4QqpJB/C9lvOMe3sptp4Moy27z 8rgem6XhBIrff91F4H2AEECI7GYDJ X-Received: by 2002:a05:6402:1842:b0:4fd:21a6:a649 with SMTP id v2-20020a056402184200b004fd21a6a649mr28884550edy.40.1680534414287; Mon, 03 Apr 2023 08:06:54 -0700 (PDT) X-Google-Smtp-Source: AKy350aI4Aq4a5QDKVoZ2QKRSmzeCqO7cLjoLBsmFhSxb9Lpx1R8DL5KQpptipgenHuWe5X8tYwmKg== X-Received: by 2002:a05:6402:1842:b0:4fd:21a6:a649 with SMTP id v2-20020a056402184200b004fd21a6a649mr28884529edy.40.1680534413999; Mon, 03 Apr 2023 08:06:53 -0700 (PDT) Date: Mon, 3 Apr 2023 11:06:49 -0400 From: "Michael S. Tsirkin" To: Parav Pandit Cc: "virtio-dev@lists.oasis-open.org" , "cohuck@redhat.com" , "virtio-comment@lists.oasis-open.org" , Shahaf Shuler Message-ID: <20230403110320-mutt-send-email-mst@kernel.org> References: <20230330225834.506969-1-parav@nvidia.com> <20230331024500-mutt-send-email-mst@kernel.org> <0dcd9907-4bb0-ef0d-678d-5bc8f0ded9ec@nvidia.com> <20230403105050-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: [PATCH 00/11] Introduce transitional mmr pci device On Mon, Apr 03, 2023 at 02:57:26PM +0000, Parav Pandit wrote: > > > > From: Michael S. Tsirkin > > Sent: Monday, April 3, 2023 10:53 AM > > > > On Fri, Mar 31, 2023 at 05:43:11PM -0400, Parav Pandit wrote: > > > > I can not say I thought about this > > > > deeply so maybe there's some problem, or maybe it's a worse approach > > > > - could you comment on this? It looks like this could be a smaller > > > > change, but maybe it isn't? Did you consider this option? > > > > > > We can possibly let both the options open for device vendors to implement. > > > > > > Change wise transport VQ is fairly big addition for both hypervisor > > > driver and also for the device. > > > > OTOH it is presumably required for scalability anyway, no? > No. > Most new generation SIOV and SR-IOV devices operate without any para-virtualization. Don't see the connection to PV. You need an emulation layer in the host if you want to run legacy guests. Looks like it could do transport vq just as well. > > And presumably it can all be done in firmware ... > > Is there actual hardware that can't implement transport vq but is going to > > implement the mmr spec? > > > Nvidia and Marvell DPUs implement MMR spec. Hmm implement it in what sense exactly? > Transport VQ has very high latency and DMA overheads for 2 to 4 bytes read/write. How many of these 2 byte accesses trigger from a typical guest? > And before discussing "why not that approach", lets finish reviewing "this approach" first. That's a weird way to put it. We don't want so many ways to do legacy if we can help it. -- MST --------------------------------------------------------------------- To unsubscribe, e-mail: virtio-dev-unsubscribe@lists.oasis-open.org For additional commands, e-mail: virtio-dev-help@lists.oasis-open.org