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=-3.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 BE835C433B4 for ; Wed, 14 Apr 2021 09:38:55 +0000 (UTC) Received: from smtp2.osuosl.org (smtp2.osuosl.org [140.211.166.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 5DE6C61222 for ; Wed, 14 Apr 2021 09:38:55 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5DE6C61222 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=virtualization-bounces@lists.linux-foundation.org Received: from localhost (localhost [127.0.0.1]) by smtp2.osuosl.org (Postfix) with ESMTP id 2333D40167; Wed, 14 Apr 2021 09:38:55 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from smtp2.osuosl.org ([127.0.0.1]) by localhost (smtp2.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id jWc8__8X2ogQ; Wed, 14 Apr 2021 09:38:54 +0000 (UTC) Received: from lists.linuxfoundation.org (lf-lists.osuosl.org [140.211.9.56]) by smtp2.osuosl.org (Postfix) with ESMTP id A80474013E; Wed, 14 Apr 2021 09:38:53 +0000 (UTC) Received: from lf-lists.osuosl.org (localhost [127.0.0.1]) by lists.linuxfoundation.org (Postfix) with ESMTP id 52B2DC000C; Wed, 14 Apr 2021 09:38:53 +0000 (UTC) Received: from smtp1.osuosl.org (smtp1.osuosl.org [140.211.166.138]) by lists.linuxfoundation.org (Postfix) with ESMTP id 8D05FC000A for ; Wed, 14 Apr 2021 09:38:52 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by smtp1.osuosl.org (Postfix) with ESMTP id 7BD358464A for ; Wed, 14 Apr 2021 09:38:52 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Authentication-Results: smtp1.osuosl.org (amavisd-new); dkim=pass (1024-bit key) header.d=redhat.com Received: from smtp1.osuosl.org ([127.0.0.1]) by localhost (smtp1.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id Noleay1koqE9 for ; Wed, 14 Apr 2021 09:38:50 +0000 (UTC) X-Greylist: domain auto-whitelisted by SQLgrey-1.8.0 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [63.128.21.124]) by smtp1.osuosl.org (Postfix) with ESMTPS id 584A7845F9 for ; Wed, 14 Apr 2021 09:38:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1618393129; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=lalZc/1rI+lVJo0eVoE/lJp+eH10vNd++g6zak8QyqE=; b=G0/UkHKMbwvcHP6HK4bSxPhhYGrzxs1av83pMAHglLF1XhW9T4iL+xlLsS378GaKCqiUf/ JuaJSlgYGRTi+cNjK7DG2qfuHg3Tb1cqZLGW+N+ftoK08sRo81hACnb39ALIWBkaLWrGQe tDIxFYwI18TfPq33uGqDb0uDHIJMItg= Received: from mail-ej1-f69.google.com (mail-ej1-f69.google.com [209.85.218.69]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-578-XU-pLwYHOem-2zMTnbhcyg-1; Wed, 14 Apr 2021 05:38:46 -0400 X-MC-Unique: XU-pLwYHOem-2zMTnbhcyg-1 Received: by mail-ej1-f69.google.com with SMTP id cd13so258168ejb.9 for ; Wed, 14 Apr 2021 02:38:45 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=lalZc/1rI+lVJo0eVoE/lJp+eH10vNd++g6zak8QyqE=; b=S/9LS1+WSRz5ge+NPZuiqJmcbTVHGk5cxNmfnGTNj5+RBAz5DWR9KC9lBuP/oQcLA2 5s9nvlgDtyg0wdPxP4vN9lXj0u1Xro8dZcX4EJYFj5PN1JZ3eedi6D5PFyfA2TZk1JA3 W3u+g6R1UNtuKzE0N6hDCy9p1wJ2/2E2dtSw/yOyaK8k83rvDt7SUwLv9Ld4M94yn5W4 pfxkin/XM0frT7hVeHOjVLyMMRHOz6l0FA5hYuFZ+4ID5SOrHOjsmPdHWBNPXOKUEvyr EYe0pweHr2zc34QBBTLPAezd+GSiViWflr48Av4O4D6RnZA1CztE+WWiDr+nG5joc95e R4Vw== X-Gm-Message-State: AOAM531OOyNw7bOh8Yrua4SLVQ4TbiSMm6I9/op9rbEF5yNSkpAQT4ZC 45N/61mQUF/5vkmrIHwoH/vMw4DgcWcW/7eTojLX37K8AKm00y/m+/uUW+qOduux+n2qLfwnKtS MarG4lFjuUsiM676BX5fHBha8K7OgCPvRbRc5DLloKQ== X-Received: by 2002:a17:906:6d12:: with SMTP id m18mr22031721ejr.435.1618393124760; Wed, 14 Apr 2021 02:38:44 -0700 (PDT) X-Google-Smtp-Source: ABdhPJzcFEOZlRdGAfhEv5zQ/EyqcpDT8X5SyssWtaqG6IyCSC68m8br91luE2LM+vWRfLVTQO26IQ== X-Received: by 2002:a17:906:6d12:: with SMTP id m18mr22031703ejr.435.1618393124579; Wed, 14 Apr 2021 02:38:44 -0700 (PDT) Received: from steredhat (host-79-34-249-199.business.telecomitalia.it. [79.34.249.199]) by smtp.gmail.com with ESMTPSA id e11sm7454837ejn.100.2021.04.14.02.38.43 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 14 Apr 2021 02:38:44 -0700 (PDT) Date: Wed, 14 Apr 2021 11:38:41 +0200 From: Stefano Garzarella To: "Michael S. Tsirkin" , "Jiang Wang ." Subject: Re: [RFC v2] virtio-vsock: add description for datagram type Message-ID: <20210414093841.koerx2wsmszv4nnj@steredhat> References: <20210412142133.t44pn5pjy6fdcvk4@steredhat> <20210413125853.2dkldmp23vkkc74c@steredhat> <20210413091251-mutt-send-email-mst@kernel.org> <20210413133852.ebkrlbyetiqu4uje@steredhat> <20210413094722-mutt-send-email-mst@kernel.org> <20210413140351.6vmffxqnj4azpyzx@steredhat> <20210413155635-mutt-send-email-mst@kernel.org> <20210414065706.inmjuoxsexejbbxj@steredhat> <20210414031220-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 In-Reply-To: <20210414031220-mutt-send-email-mst@kernel.org> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=sgarzare@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Disposition: inline Cc: cong.wang@bytedance.com, Xiongchun Duan , cohuck@redhat.com, virtualization@lists.linux-foundation.org, xieyongji@bytedance.com, Stefan Hajnoczi , asias@redhat.com, Arseny Krasnov X-BeenThere: virtualization@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Linux virtualization List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Errors-To: virtualization-bounces@lists.linux-foundation.org Sender: "Virtualization" On Wed, Apr 14, 2021 at 03:20:07AM -0400, Michael S. Tsirkin wrote: >On Wed, Apr 14, 2021 at 08:57:06AM +0200, Stefano Garzarella wrote: >> On Tue, Apr 13, 2021 at 03:58:34PM -0400, Michael S. Tsirkin wrote: >> > On Tue, Apr 13, 2021 at 04:03:51PM +0200, Stefano Garzarella wrote: >> > > On Tue, Apr 13, 2021 at 09:50:45AM -0400, Michael S. Tsirkin wrote: >> > > > On Tue, Apr 13, 2021 at 03:38:52PM +0200, Stefano Garzarella wrote: >> > > > > On Tue, Apr 13, 2021 at 09:16:50AM -0400, Michael S. Tsirkin wrote: >> > > > > > On Tue, Apr 13, 2021 at 02:58:53PM +0200, Stefano Garzarella wrote: >> > > > > > > On Mon, Apr 12, 2021 at 03:42:23PM -0700, Jiang Wang . wrote: >> > > > > > > > On Mon, Apr 12, 2021 at 7:21 AM Stefano Garzarella wrote: >> > > > > > > > > >> > > > > > > > > On Mon, Apr 12, 2021 at 02:50:17PM +0100, Stefan Hajnoczi wrote: >> > > > > > > > > >On Thu, Apr 01, 2021 at 04:36:02AM +0000, jiang.wang >> > > > > > > > > >wrote: [...] >> > > > > > > > > >> >> > > > > > > > > >> +Datagram sockets provide connectionless unreliable messages of >> > > > > > > > > >> +a fixed maximum length. >> > > > > > > > > > >> > > > > > > > > >Plus unordered (?) and with message boundaries. In other words: >> > > > > > > > > > >> > > > > > > > > > Datagram sockets provide unordered, unreliable, connectionless message >> > > > > > > > > > with message boundaries and a fixed maximum length. >> > > > > > > > > > >> > > > > > > > > >I didn't think of the fixed maximum length aspect before. I guess the >> > > > > > > > > >intention is that the rx buffer size is the message size limit? That's >> > > > > > > > > >different from UDP messages, which can be fragmented into multiple IP >> > > > > > > > > >packets and can be larger than 64KiB: >> > > > > > > > > >https://en.wikipedia.org/wiki/User_Datagram_Protocol#UDP_datagram_structure >> > > > > > > > > > >> > > > > > > > > >Is it possible to support large datagram messages in vsock? I'm a little >> > > > > > > > > >concerned that applications that run successfully over UDP will not be >> > > > > > > > > >portable if vsock has this limitation because it would impose extra >> > > > > > > > > >message boundaries that the application protocol might not tolerate. >> > > > > > > > > >> > > > > > > > > Maybe we can reuse the same approach Arseny is using for SEQPACKET. >> > > > > > > > > Fragment the packets according to the buffers in the virtqueue and set >> > > > > > > > > the EOR flag to indicate the last packet in the message. >> > > > > > > > > >> > > > > > > > Agree. Another option is to use the ones for skb since we may need to >> > > > > > > > use skbs for multiple transport support anyway. >> > > > > > > > >> > > > > > > >> > > > > > > The important thing I think is to have a single flag in virtio-vsock that >> > > > > > > identifies pretty much the same thing: this is the last fragment of a series >> > > > > > > to rebuild a packet. >> > > > > > > >> > > > > > > We should reuse the same flag for DGRAM and SEQPACKET. >> > > > > > > >> > > > > > > Thanks, >> > > > > > > Stefano >> > > > > > >> > > > > > Well DGRAM can drop data so I wonder whether it can work ... >> > > > > > >> > > > > >> > > > > Yep, this is true, but the channel should not be losing packets, so if the >> > > > > receiver discards packets, it knows that it must then discard all of them >> > > > > until the EOR. >> > > > >> > > > That is not so easy - they can come mixed up from multiple sources. >> > > >> > > I think we can prevent mixing because virtuqueue is point to point and its >> > > use is not thread safe, so the access (in the same peer) is already >> > > serialized. >> > > In the end the packet would be fragmented only before copying it to the >> > > virtuqueue. >> > > >> > > But maybe I missed something... >> > >> > Well I ask what's the point of fragmenting then. I assume it's so we >> > can pass huge messages around so you can't keep locks ... >> > >> >> Maybe I'm wrong, but isn't this similar to what we do in virtio-net with >> mergeable buffers? > >The point of mergeable buffers is to use less memory: both for each >packet and for a full receive vq. > >> Also in this case I think the fragmentation will happen only in the device, >> since the driver can enqueue the entire buffer. >> >> Maybe we can reuse mergeable buffers for virtio-vsock if the EOR flag is not >> suitable. > >That sounds very reasonable. It should also allow us to save the header for each fragment. @Jiang Do you want to explore this? I'm talking about VIRTIO_NET_F_MRG_RXBUF feature. > >> IIUC in the vsock device the fragmentation for DGRAM will happen just >> before >> to queue it in the virtqueue, and the device can check how many buffers are >> available in the queue and it can decide whether to queue them all up or >> throw them away. >> > >> > > > Sure linux net core does this but with fragmentation added in, >> > > > I start wondering whether you are beginning to reinvent the net stack >> > > > ... >> > > >> > > No, I hope not :-), in the end our advantage is that we have a channel that >> > > doesn't lose packets, so I guess we can make assumptions that the network >> > > stack can't. >> > > >> > > Thanks, >> > > Stefano >> > >> > I still don't know how will credit accounting work for datagram, >> > but proposals I saw seem to actually lose packets ... >> > >> >> I still don't know too, but I think it's not an issue in the RX side, >> since if it doesn't have space, can drop all the fragment. >> >> Another option to avoid fragmentation could be to allocate 64K buffers for >> the new DGRAM virtqueue. > >That's a lot of buffers ... Yep I see, and they would often be mostly unused... > >> In this way we will have at most 64K packets, which is similar to >> UDP/IP, >> without extra work for the fragmentation. > >IIRC default MTU is 1280 not 64K ... I was thinking that UDP at most can support 64K messages that IP should fragment according to MTU. Thanks, Stefano _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization