Received: by 2002:a05:6a10:a0d1:0:0:0:0 with SMTP id j17csp2179963pxa; Mon, 3 Aug 2020 09:21:42 -0700 (PDT) X-Google-Smtp-Source: ABdhPJx7LTIOKmDSywDDepogmA1WmwGmbNHh36KuLbX3lsnQpCaHlcpefEKW25ZDlhGJ7XobZzZl X-Received: by 2002:a17:906:7fc9:: with SMTP id r9mr16951885ejs.407.1596471702149; Mon, 03 Aug 2020 09:21:42 -0700 (PDT) ARC-Seal: i=1; a=rsa-sha256; t=1596471702; cv=none; d=google.com; s=arc-20160816; b=LsAt3GCdp3c3yYu7CBsKLazr/p8g4WXMieRAowD+w+6B3ybPHRy3CT/JvZ85SpKTlz 2w8NT1hOC0OcidDonnyigW3XxOQYK2CM4QjbZDhW2tGvp0z7C8qIyutGBIyuY5zBAp3D ZflBR3vYj6VIqhAcBD4JLkP37BaPSQCk0FEDRsOGsNcTJwXeQuj1gxCq3V9Xnk8ILgQT 6CkVau63Pl7+JTx9vU5yZ2yoDMoEDrSFtI5uwhyqbkUO5Mk4lOaiiZkJF7CvLRrFdZDK wX95X6T/7VISQYbV/PCDNDGpfv4tUQ7SXI5c/oYB5O2HcrNWX+nMRemDKSFRkHpi256V qS5A== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=list-id:precedence:sender:content-transfer-encoding:mime-version :message-id:date:in-reply-to:subject:cc:to:from:user-agent :references:dkim-signature; bh=tLldRhiZuUDIQWR4Dezuv3wy8y8ie+Yklp9pb5zDPYU=; b=tkjkB167vVkG7BgL/76XdPcNRPDAkg2vnhxdo8DIlEOs8ZQMq9Ft0r14u/N7dcJ9nu s8Q/nV26/CJN2JkExoF9Vk1VUBDHL/Zd4Lw75ZXbsFNBU5UbtZMT/+/0zcd3scpvJigA au+rTSwQZ2MkMddLoYs7f/4layTz+xXFp3UgJtwtaem1KoXaq7NZ4H2lcCAnsPWwyci8 Fhw+ycjJdfDU5bsa0OY4p0Lb/fUfnAcB7jW6I7Y020JlVLjWuTxR4vG9x6dj2ZsEaGV7 V+u+8CoyooUegdC/o6U8FSecpIqNu7XyXH3pvkKjmN8mddefI/mL5ZQHkfdvIcaVS48D jIdA== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@linaro.org header.s=google header.b=kArTRLvh; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=linaro.org Return-Path: Received: from vger.kernel.org (vger.kernel.org. [23.128.96.18]) by mx.google.com with ESMTP id cq22si9372463edb.609.2020.08.03.09.21.19; Mon, 03 Aug 2020 09:21:42 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18; Authentication-Results: mx.google.com; dkim=pass header.i=@linaro.org header.s=google header.b=kArTRLvh; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=linaro.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728224AbgHCQUA (ORCPT + 99 others); Mon, 3 Aug 2020 12:20:00 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50146 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726239AbgHCQUA (ORCPT ); Mon, 3 Aug 2020 12:20:00 -0400 Received: from mail-wm1-x342.google.com (mail-wm1-x342.google.com [IPv6:2a00:1450:4864:20::342]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D39C3C06174A for ; Mon, 3 Aug 2020 09:19:59 -0700 (PDT) Received: by mail-wm1-x342.google.com with SMTP id x5so142096wmi.2 for ; Mon, 03 Aug 2020 09:19:59 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=references:user-agent:from:to:cc:subject:in-reply-to:date :message-id:mime-version:content-transfer-encoding; bh=tLldRhiZuUDIQWR4Dezuv3wy8y8ie+Yklp9pb5zDPYU=; b=kArTRLvhvEX48jCt3FGfAjBk5q2jKd9B5OHtI2t2LNYcIwOE9g/YdRTu0Qv2/tKSjZ lY/8hKN+3rz/dF3zh17SF08NDzr2v5tDF/bmP2o3etZF2ZPLCzZHQcwvFYvP6duA+NJ3 6za7Y2F5OxqbdFHHrY1qkFYEnEsvOLhqBgPImgSNCH+YWCrqy1GbmClVWNkQttM0crWO C4IQK3mx0BVlHvD4+D5Htf5fo+OiwQlVb3itNqCmv/ZX4igDhj4tmx5+XJdBG4sPULc7 qxE59tZVZk2eDk6LpYf2ts74W/NPd1IpRDd0Trdw+2MgpJu1EV4Jsb0p42NlJh7mWqSo Hyng== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:references:user-agent:from:to:cc:subject :in-reply-to:date:message-id:mime-version:content-transfer-encoding; bh=tLldRhiZuUDIQWR4Dezuv3wy8y8ie+Yklp9pb5zDPYU=; b=B2J6XUwAmjF79DLCAg3IzPvOCEGSV/KY25oY9urw6ra5DQ5NEXBjYcYB4BBmcsvmOw Cc1/FfGUWPnpcUgS485cB5XakomVI2SOHA1QYGEfThjnZ/1cJTku6ji6VFZRs20uHqJL gZ/MuWF2a68e080EK9l1xynRrs6h2qvIakjLPSG1ky8idDSEA7NwzciHynJhlOLZX3a7 j1Bit+h6AvAcssnN0icscl74qwyuElkHNtJ6Z4I+B62+Kjzvspb53+JX6XlrsCCq9PEW 2F/ZHXWFT60evojvp8has3/F2MdfUfgjDmwey8nCD4BSsCQzoaCEbv398BzCYcFcNqWP DJbw== X-Gm-Message-State: AOAM532HCSg19yP9uq9+GpE00y/2VjOlpcqO2xMHBbq2LkEROguINS29 8Ut0ZTXGXqdS6TRbDyKaBV98CSwdWLM= X-Received: by 2002:a7b:c084:: with SMTP id r4mr56952wmh.23.1596471598552; Mon, 03 Aug 2020 09:19:58 -0700 (PDT) Received: from zen.linaroharston ([51.148.130.216]) by smtp.gmail.com with ESMTPSA id n24sm50772wmi.36.2020.08.03.09.19.57 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 03 Aug 2020 09:19:57 -0700 (PDT) Received: from zen (localhost [127.0.0.1]) by zen.linaroharston (Postfix) with ESMTP id A8FBE1FF7E; Mon, 3 Aug 2020 17:19:56 +0100 (BST) References: <87ft973d0b.fsf@linaro.org> User-agent: mu4e 1.5.5; emacs 28.0.50 From: Alex =?utf-8?Q?Benn=C3=A9e?= To: "Pincus, Josh" Cc: "linux-kernel@vger.kernel.org" , "zhabin@linux.alibaba.com" , "virtio-dev@lists.oasis-open.org" , qemu-devel@nongnu.org Subject: Re: [PATCH v2 0/5] virtio mmio specification enhancement In-reply-to: <87ft973d0b.fsf@linaro.org> Date: Mon, 03 Aug 2020 17:19:56 +0100 Message-ID: <87wo2fn1lf.fsf@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Alex Benn=C3=A9e writes: > Pincus, Josh writes: > >> Hi, >> >>=20=20 >> >> We were looking into a similar enhancement for the Virt I/O MMIO transpo= rt and came across this project. >> >> This enhancement would be perfect for us. > > So there is certainly an interest in optimising MMIO based virtio and > the current read/ack cycle adds additional round trip time for any trap > and emulate hypervisor. However I think there is some resistance to > making MMIO a re-implementation of what PCI already gives us for "free". > > - Quantifying the memory foot-print difference between PCI/MMIO > > PCI gives a lot for free including a discovery and IRQ model already > designed to handle MSI/MSI-X. There is a claim that this brings in a > lot of bloat but I think there was some debate around the numbers. > My rough initial experiment with a PCI and non-PCI build with > otherwise identical VIRTIO configs results in the following: > > 16:40:15 c.282% [alex@zen:~/l/l/builds] review/rpmb|=E2=80=A6 + ls -l= arm64/vmlinux arm64.nopci/vmlinux > -rwxr-xr-x 1 alex alex 83914728 Jul 31 16:39 arm64.nopci/vmlinux* > -rwxr-xr-x 1 alex alex 86368080 Jul 31 16:33 arm64/vmlinux* > > which certainly implies there could be a fair amount of headroom for > an MMIO version to implement some features. However I don't know if > it's fully apples to apples as there maybe unneeded PCI bloat that a > virtio-only kernel doesn't need. Just following up after cutting the Xgene and ThunderX PCI bloat from the kernel the margin is a little smaller: -rwxr-xr-x 1 alex alex 83914728 Jul 31 16:39 arm64.nopci/vmlinux* -rwxr-xr-x 1 alex alex 85639808 Aug 3 17:12 arm64/vmlinux* --=20 Alex Benn=C3=A9e