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=-4.1 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 F1FEAC433DF for ; Fri, 31 Jul 2020 15:44:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CAA942072A for ; Fri, 31 Jul 2020 15:44:42 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=linaro.org header.i=@linaro.org header.b="q9wLsEV1" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387500AbgGaPol (ORCPT ); Fri, 31 Jul 2020 11:44:41 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33966 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726502AbgGaPok (ORCPT ); Fri, 31 Jul 2020 11:44:40 -0400 Received: from mail-wm1-x344.google.com (mail-wm1-x344.google.com [IPv6:2a00:1450:4864:20::344]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6760DC061574 for ; Fri, 31 Jul 2020 08:44:40 -0700 (PDT) Received: by mail-wm1-x344.google.com with SMTP id k8so9662612wma.2 for ; Fri, 31 Jul 2020 08:44:40 -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=1NYpUqU0m8gseMafnU6ZZ9hI2VDqh8nRMV7j1ON+eBM=; b=q9wLsEV1Rk86emsF/ZMka41GeXSH8p2UuNxu72NK83TrraoBOj3KbElFDqyWMg1Y2g j8+WWomQ3hG03JaVGL7Bhmm0jpbWFfAhnVv5wr9afd9LWsDuoy57zt2jtf7n4HCFenNG S85eCT7lkHJhQztLKwwXArDfMi2EmCLZ36ZFzeSG1qK63Tnq3BN7uA/TbDS06o4PpFvl pQ1h9esrDazcp3tURnh1t+RofCZAjt149XtCdfM2+xT+XZ3rFt1MU9/vF5i7q1/lc7vd JqD9po/Kd3CQQhRU7oPS2q3PBy4eMa/ZE625Ijs+kfu6j+QvY1FeO5AOInX4b2YoBeWo pVLA== 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=1NYpUqU0m8gseMafnU6ZZ9hI2VDqh8nRMV7j1ON+eBM=; b=lUwJIbj+Btw0ShB9pm4YMCBpzVrvNyUr5S+SoZ2KkVaAfplBEIe/vt9c5SHBLWRZHo pDeS58EHmf9m/y5frQ2lCsvAIJMWHlBtpVt7PSxzudHnTki+H+PZ1wQd58p2Qrvv3NdG VZb7qq4GA4tHIlIjPYOLA/FdZXcGoL+2sDqJ6JCXnAqJGWx+Tzb3bQYOXQ33ZAt7zNl6 peYSz3zYemR6Io1fvQV2leWKJaaeNrG7QdersGiACXBPCLwcocdAgQOylI+qpus+CVm8 YiabYRVq0FIgvhtzoZvt0grra4z+26UK+yfg6v3apgpY18s6yylOSTm+zjl4yaFKI3cf vkKg== X-Gm-Message-State: AOAM532fDpDhuwrPp57z/jtMVC1UGNNZSnIR5ms6DczmbCkajOvFVgks kGR9ARi5WsxN9jOLobLJjx9NCDiux6o= X-Google-Smtp-Source: ABdhPJwhf6SCj36hK7ZvgS64rGdD6hgF4XvKN/y4k6M39iiUOCVksDr6o5wKsJmPgR7W23rm4JetFQ== X-Received: by 2002:a7b:c5c5:: with SMTP id n5mr4404346wmk.103.1596210278258; Fri, 31 Jul 2020 08:44:38 -0700 (PDT) Received: from zen.linaroharston ([51.148.130.216]) by smtp.gmail.com with ESMTPSA id w64sm12242643wmb.26.2020.07.31.08.44.37 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 31 Jul 2020 08:44:37 -0700 (PDT) Received: from zen (localhost [127.0.0.1]) by zen.linaroharston (Postfix) with ESMTP id 2DCB81FF7E; Fri, 31 Jul 2020 16:44:36 +0100 (BST) References: 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: Date: Fri, 31 Jul 2020 16:44:36 +0100 Message-ID: <87ft973d0b.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 Pincus, Josh writes: > Hi, > >=20=20 > > We were looking into a similar enhancement for the Virt I/O MMIO transpor= t 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". I believe the current questions that need to be addressed are: - Clear definitions in the spec on doorbells/notifications The current virtio spec uses different terms in some places so it would be nice to clarify the language and formalise what the standard expects from transports w.r.t the capabilities of notifications and doorbells. - 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 a= rm64/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. What are the features you are most interested in? > Has there been any progress since Feb, 2020? It looks like the effort > might have stalled? I can't speak to the OP's but there is certainly interest from others that are not the original posters. --=20 Alex Benn=C3=A9e