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 37882C76196 for ; Mon, 3 Apr 2023 15:23:20 +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 90C2D3DF27 for ; Mon, 3 Apr 2023 15:23:19 +0000 (UTC) Received: from lists.oasis-open.org (oasis-open.org [10.110.1.242]) by lists.oasis-open.org (Postfix) with ESMTP id 8567D9863FE for ; Mon, 3 Apr 2023 15:23:19 +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 7B1DC9863DF; Mon, 3 Apr 2023 15:23:19 +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 66FF59863DE for ; Mon, 3 Apr 2023 15:23:14 +0000 (UTC) X-Virus-Scanned: amavisd-new at kavi.com X-MC-Unique: iujV2L4yOjiYpcMBtlc8_g-1 X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; t=1680535391; 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=ie+9l506BIJC9elguckI8ioIKISNJPQKx/yp3ZtyNMs=; b=J185pBUbcy+Fjcef54nV4MWpLUsOSwT74X70QzslH/j9YEXZ/PbCcv+wZthzmy+coZ 67SxaMiCUXpBr2dOcLm4sJKwz0u7lj3Hz3yMvGjobay6womGr/EzEyA0Oiz6MsM12a17 HYBgf7zllVCV2SCSI2oL6gkWw/N80vWQkwYuX4AzPOHkONNfMbBqAfDDdyrG2ykqDvfD pl8GqlxAt1WoRWqkzGUv/thRzCzZoEOPRTsZtiR3GgQZfCbu/yPcWF28cMgrtSjZwFzD UIG+CPIJT/1tLEuzxf/tiEIgOnFqDCD0WCEf3qySdIETlkbYTPw1ohDgb9Mp65Kr/1rs 9vpw== X-Gm-Message-State: AAQBX9cGTD2NbHZEKPng3fI9Yb+zzu7QinPS3iRHtLG63Q1gWpvoPnIF 0YhSRPulyG3c1R5fUhEXAIdNqA/uHhiXuhv/Bgqv7IcjPR8vgJF/W+517MkyIkncwTBFSupBA3Q DP3MTkiKuq1kZQTOqx6uouThSwDPFu8s3UhzJ+Vxqyw== X-Received: by 2002:a17:906:174b:b0:929:7d80:3a37 with SMTP id d11-20020a170906174b00b009297d803a37mr34857090eje.37.1680535391329; Mon, 03 Apr 2023 08:23:11 -0700 (PDT) X-Google-Smtp-Source: AKy350bH6GnppWPLhPpXwy3fuly/GUnxMRu17exlTDNC6TkQsqtv+bcORgUtSBFQUWDPWYF4snCc/w== X-Received: by 2002:a17:906:174b:b0:929:7d80:3a37 with SMTP id d11-20020a170906174b00b009297d803a37mr34857069eje.37.1680535391060; Mon, 03 Apr 2023 08:23:11 -0700 (PDT) Date: Mon, 3 Apr 2023 11:23:05 -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: <20230403111735-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> <20230403110320-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 03:16:53PM +0000, Parav Pandit wrote: > > > > From: Michael S. Tsirkin > > Sent: Monday, April 3, 2023 11:07 AM > > > > > 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. > > > Transport vq for legacy MMR purpose seems fine with its latency and DMA overheads. > Your question was about "scalability". > After your latest response, I am unclear what "scalability" means. > Do you mean saving the register space in the PCI device? yes that's how you used scalability in the past. > If yes, than, no for legacy guests for scalability it is not required, because the legacy register is subset of 1.x. Weird. what does guest being legacy have to do with a wish to save registers on the host hardware? You don't have so many legacy guests as modern guests? Why? > > > > > 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? > > > Do not follow the question. > The proposed series will be implemented as PCI SR-IOV devices using MMR spec. > > > > 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? > > > Mostly during the VM boot time. 20 to 40 registers read write access. That is not a lot! How long does a DMA operation take then? > > > 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. > Sure, so lets finish the review of current proposal details. > At the moment > a. I don't see any visible gain of transport VQ other than device reset part I explained. For example, we do not need a new range of device IDs and existing drivers can bind on the host. > b. it can be a way with high latency, DMA overheads on the virtqueue for read/writes for small access. numbers? -- MST --------------------------------------------------------------------- To unsubscribe, e-mail: virtio-dev-unsubscribe@lists.oasis-open.org For additional commands, e-mail: virtio-dev-help@lists.oasis-open.org