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 EB630C77B73 for ; Wed, 12 Apr 2023 04:20:28 +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 403D62B01F for ; Wed, 12 Apr 2023 04:20:28 +0000 (UTC) Received: from lists.oasis-open.org (oasis-open.org [10.110.1.242]) by lists.oasis-open.org (Postfix) with ESMTP id 21D58986511 for ; Wed, 12 Apr 2023 04:20:28 +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 09DC69864B3; Wed, 12 Apr 2023 04:20:28 +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 E328F98650E for ; Wed, 12 Apr 2023 04:20:17 +0000 (UTC) X-Virus-Scanned: amavisd-new at kavi.com X-MC-Unique: oleIworpPR2OtUT8SnNp7w-1 X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; t=1681273214; h=in-reply-to:content-transfer-encoding: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=nKJYIrn2LtPWj3lT6FVEwJs5C92bnXjn3LdSC9a5fvQ=; b=SmFfig+PXtv0M3J5n0k2QoDCw/mVVTFq0izlKXDThmWKvEE+rltsEBsWbPQDQwczNX brD/RQvFdGw16Zuag7UhokPQHi31FvuLIv7W9tXNWiHorWWLYChr6nZSIOqrtgFAKMkF anHiEQMpQLSqVXZwXFbROBmMSpyN/93rLG0pH64QK6kBu0MnBadWo9zAs9x2rN7rp3sg 9vc9PHYHOL9IvP5NvBTZQmDiyCH7nQG5CoW1wqeiFrlcjTPc82f3jgVSruroV/bfvWW2 4ugjSw5pqyhOMs8dlciGOMUKlv4mRripvg4JkhN28o/afcfpEqZxetswarT/xS2pkEVD /Z8A== X-Gm-Message-State: AAQBX9dWnQPHwwtna6QnZc5XPf0dvtljGUXejby9wGO00LHsBA/HwUBJ U1ChlHMicRbMgWuzWLhZCNbID1Bc9oKtyIFh+UPHbX2xJMuyEmcnp2rvUcxSCvwdgfJXH7RRcWo oUh6vxpV8rC1+jet5s7ygZtrH/gRF X-Received: by 2002:a5d:4090:0:b0:2f4:3b2c:1b2e with SMTP id o16-20020a5d4090000000b002f43b2c1b2emr813717wrp.31.1681273214261; Tue, 11 Apr 2023 21:20:14 -0700 (PDT) X-Google-Smtp-Source: AKy350Zcg/9zn6jbbMwPvqAFbRIUiE15e1jmZrmghOYzX1V18CN28i1CL9We8qr2venu5yIZ1S65og== X-Received: by 2002:a5d:4090:0:b0:2f4:3b2c:1b2e with SMTP id o16-20020a5d4090000000b002f43b2c1b2emr813704wrp.31.1681273213968; Tue, 11 Apr 2023 21:20:13 -0700 (PDT) Date: Wed, 12 Apr 2023 00:20:10 -0400 From: "Michael S. Tsirkin" To: Jason Wang Cc: Parav Pandit , "virtio-dev@lists.oasis-open.org" , "cohuck@redhat.com" , "virtio-comment@lists.oasis-open.org" , Shahaf Shuler , Satananda Burla Message-ID: <20230412001803-mutt-send-email-mst@kernel.org> References: <20230330225834.506969-1-parav@nvidia.com> <20230330225834.506969-9-parav@nvidia.com> <307a9f8f-6184-0403-97ab-1b1c16d4fd3c@nvidia.com> <20230411172207-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=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit Subject: Re: [virtio-dev] [PATCH 08/11] transport-pci: Introduce virtio extended capability On Wed, Apr 12, 2023 at 12:07:26PM +0800, Jason Wang wrote: > On Wed, Apr 12, 2023 at 5:25 AM Michael S. Tsirkin wrote: > > > > On Tue, Apr 11, 2023 at 07:01:16PM +0000, Parav Pandit wrote: > > > > > > > From: virtio-dev@lists.oasis-open.org On > > > > Behalf Of Jason Wang > > > > Sent: Monday, April 10, 2023 11:29 PM > > > > > > > > However, it is not backward compatible, if the device place them in > > > > > extended capability, it will not work. > > > > > > > > > > > > > It is kind of intended since it is only used for new PCI-E features: > > > > > > > New fields in new extended pci cap area is fine. > > > Migrating old fields to be present in the new extended pci cap, is not your intention. Right? > > > > > > > " > > > > +The location of the virtio structures that depend on the PCI Express > > > > +capability are specified using a vendor-specific extended capabilities > > > > +on the extended capabilities list in PCI Express extended configuration > > > > +space of the device. > > > > " > > > > > > > > > To make it backward compatible, a device needs to expose existing > > > > > structure in legacy area. And extended structure for same capability > > > > > in extended pci capability region. > > > > > > > > > > In other words, it will have to be a both places. > > > > > > > > Then we will run out of config space again? > > > No. > > > Only currently defined caps to be placed in two places. > > > New fields don’t need to be placed in PCI cap, because no driver is looking there. > > > > > > We probably already discussed this in previous email by now. > > > > > > > Otherwise we need to deal with the > > > > case when existing structures were only placed at extended capability. Michael > > > > suggest to add a new feature, but the driver may not negotiate the feature > > > > which requires more thought. > > > > > > > Not sure I understand feature bit. > > > > This is because we have a concept of dependency between > > features but not a concept of dependency of feature on > > capability. > > > > > PCI transport fields existence is usually not dependent on upper layer protocol. > > > > > > > > We may need it even sooner than this because the AQ patch is expanding > > > > > the structure located in legacy area. > > > > > > > > Just to make sure I understand this, assuming we have adminq, any reason a > > > > dedicated pcie ext cap is required? > > > > > > > No. it was my short sight. I responded right after above text that AQ doesn’t need cap extension. > > > > > > > > You know, thinking about this, I begin to feel that we should > > require that if at least one extended config exists then > > all caps present in the regular config are *also* > > mirrored in the extended config. IOW extended >= regular. > > The reason is that extended config can be emulated more efficiently > > (2x less exits). > > Any reason for it to get less exits? For a variety of reasons having to do with buggy hardware e.g. linux likes to use cf8/cfc for legacy ranges. 2 accesses are required for each read/write. extended space is just 1. > At least it has not been done in > current Qemu's emulation. (And do we really care about the performance > of config space access?) > > Thanks For boot speed, yes. Not minor 5% things but 2x, sure. > > WDYT? > > > > > > -- > > MST > > --------------------------------------------------------------------- To unsubscribe, e-mail: virtio-dev-unsubscribe@lists.oasis-open.org For additional commands, e-mail: virtio-dev-help@lists.oasis-open.org