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=-9.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,USER_AGENT_NEOMUTT autolearn=ham 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 D3568C10F13 for ; Mon, 8 Apr 2019 14:55:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 98823214C6 for ; Mon, 8 Apr 2019 14:55:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727361AbfDHOzh (ORCPT ); Mon, 8 Apr 2019 10:55:37 -0400 Received: from mail-wm1-f65.google.com ([209.85.128.65]:38963 "EHLO mail-wm1-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726510AbfDHOzh (ORCPT ); Mon, 8 Apr 2019 10:55:37 -0400 Received: by mail-wm1-f65.google.com with SMTP id n25so15065225wmk.4 for ; Mon, 08 Apr 2019 07:55:35 -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:user-agent; bh=d+VXGRvLJl/73j3SUvoZqzzhsYpvSaoUrtP7cc7XveQ=; b=sbJcM5WxuM1X4TDwnNZVAXPJnkckbsgxiHq+v5JHH65GvxCsqNNekWsVlY80L8yTif 52FDoMCKEDjvyPEblElO3z5SI+gd8gpx34motzfVSXmTl/QdiYaGCogLhX0T4RU7ZzWE loCTCknFG0e3T2cHhG5S3GnqbSfPlPGjkWkZY3lq57GxQenZ8pTr5odSFLwHufjIZhUo gBaRzjeivy8MvdewcHHJTAutt73J7V1KK//2B1CiKL+Ja1bd/A0dtV0I3ibo3jwaKttG p9uIPYgAE1tAFRWhVHpDfjfjfgwghR95Uh8utyK/ZSFf832f5pqnWs2G+F+hXGIL+qDC XBCA== X-Gm-Message-State: APjAAAU6xf5kDAU+62xIN33HmBN2xheyo1YGEs6lYjZN8rbl/22K+PAB RrFdmJrlg661l5uJjvfrG8SfyA== X-Google-Smtp-Source: APXvYqwF66ndE12RskCSuH3hhho6ZGzmohFKXkWV1NNxQNDtBZyZcKYSyxFotJYhRg8eg4klTr6iWA== X-Received: by 2002:a1c:5543:: with SMTP id j64mr9267773wmb.37.1554735335117; Mon, 08 Apr 2019 07:55:35 -0700 (PDT) Received: from steredhat (host35-203-static.12-87-b.business.telecomitalia.it. [87.12.203.35]) by smtp.gmail.com with ESMTPSA id z7sm9809225wml.40.2019.04.08.07.55.33 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Mon, 08 Apr 2019 07:55:34 -0700 (PDT) Date: Mon, 8 Apr 2019 16:55:31 +0200 From: Stefano Garzarella To: Stefan Hajnoczi Cc: Stefan Hajnoczi , netdev@vger.kernel.org, Jason Wang , "Michael S. Tsirkin" , kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org, "David S. Miller" Subject: Re: [PATCH RFC 3/4] vsock/virtio: change the maximum packet size allowed Message-ID: <20190408145531.yreyawkn5vjqj7sl@steredhat> References: <20190404105838.101559-1-sgarzare@redhat.com> <20190404105838.101559-4-sgarzare@redhat.com> <20190405082447.GD25152@stefanha-x1.localdomain> <20190405100747.dbwi3sjaudp3d2wa@steredhat> <20190408093723.GP15001@stefanha-x1.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190408093723.GP15001@stefanha-x1.localdomain> User-Agent: NeoMutt/20180716 Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Mon, Apr 08, 2019 at 10:37:23AM +0100, Stefan Hajnoczi wrote: > On Fri, Apr 05, 2019 at 12:07:47PM +0200, Stefano Garzarella wrote: > > On Fri, Apr 05, 2019 at 09:24:47AM +0100, Stefan Hajnoczi wrote: > > > On Thu, Apr 04, 2019 at 12:58:37PM +0200, Stefano Garzarella wrote: > > > > Since now we are able to split packets, we can avoid limiting > > > > their sizes to VIRTIO_VSOCK_DEFAULT_RX_BUF_SIZE. > > > > Instead, we can use VIRTIO_VSOCK_MAX_PKT_BUF_SIZE as the max > > > > packet size. > > > > > > > > Signed-off-by: Stefano Garzarella > > > > --- > > > > net/vmw_vsock/virtio_transport_common.c | 4 ++-- > > > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > > > > > diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c > > > > index f32301d823f5..822e5d07a4ec 100644 > > > > --- a/net/vmw_vsock/virtio_transport_common.c > > > > +++ b/net/vmw_vsock/virtio_transport_common.c > > > > @@ -167,8 +167,8 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk, > > > > vvs = vsk->trans; > > > > > > > > /* we can send less than pkt_len bytes */ > > > > - if (pkt_len > VIRTIO_VSOCK_DEFAULT_RX_BUF_SIZE) > > > > - pkt_len = VIRTIO_VSOCK_DEFAULT_RX_BUF_SIZE; > > > > + if (pkt_len > VIRTIO_VSOCK_MAX_PKT_BUF_SIZE) > > > > + pkt_len = VIRTIO_VSOCK_MAX_PKT_BUF_SIZE; > > > > > > The next line limits pkt_len based on available credits: > > > > > > /* virtio_transport_get_credit might return less than pkt_len credit */ > > > pkt_len = virtio_transport_get_credit(vvs, pkt_len); > > > > > > I think drivers/vhost/vsock.c:vhost_transport_do_send_pkt() now works > > > correctly even with pkt_len > VIRTIO_VSOCK_MAX_PKT_BUF_SIZE. > > > > Correct. > > > > > > > > The other ->send_pkt() callback is > > > net/vmw_vsock/virtio_transport.c:virtio_transport_send_pkt_work() and it > > > can already send any size packet. > > > > > > Do you remember why VIRTIO_VSOCK_MAX_PKT_BUF_SIZE still needs to be the > > > limit? I'm wondering if we can get rid of it now and just limit packets > > > to the available credits. > > > > There are 2 reasons why I left this limit: > > 1. When the host receives a packets, it must be <= > > VIRTIO_VSOCK_MAX_PKT_BUF_SIZE [drivers/vhost/vsock.c:vhost_vsock_alloc_pkt()] > > So in this way we can limit the packets sent from the guest. > > The general intent is to prevent the guest from sending huge buffers. > This is good. > > However, the guest must already obey the credit limit advertized by the > host. Therefore I think we should be checking against that instead of > an arbitrary constant limit. > > So I think the limit should be the receive buffer size, not > VIRTIO_VSOCK_MAX_PKT_BUF_SIZE. But at this point the code doesn't know > which connection the packet is associated with and cannot check the > receive buffer size. :( > > Anyway, any change to this behavior requires compatibility so new guest > drivers work with old vhost_vsock.ko. Therefore we should probably just > leave the limit for now. I understood your point of view and I completely agree with you. But, until we don't have a way to expose features/versions between guest and host, maybe is better to leave the limit in order to be compatible with old vhost_vsock. > > > 2. When the host send packets, it help us to increase the parallelism > > (especially if the guest has 64 KB RX buffers) because the user thread > > will split packets, calling multiple times transport->stream_enqueue() > > in net/vmw_vsock/af_vsock.c:vsock_stream_sendmsg() while the > > vhost_transport_send_pkt_work() send them to the guest. > > Sorry, I don't understand the reasoning. Overall this creates more > work. Are you saying the benefit is that > vhost_transport_send_pkt_work() can run "early" and notify the guest of > partial rx data before all of it has been enqueued? Something like that. Your reasoning is more accurate. Anyway, I'll do some tests in order to understand better the behaviour! Thanks, Stefano