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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 31356C43218 for ; Tue, 11 Jun 2019 13:19:53 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (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 0741C20673 for ; Tue, 11 Jun 2019 13:19:52 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0741C20673 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:58768 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1haggq-0008Gu-8b for qemu-devel@archiver.kernel.org; Tue, 11 Jun 2019 09:19:52 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:50177) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1haget-0007Ct-T4 for qemu-devel@nongnu.org; Tue, 11 Jun 2019 09:17:53 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hages-0003Ga-E6 for qemu-devel@nongnu.org; Tue, 11 Jun 2019 09:17:51 -0400 Received: from mx1.redhat.com ([209.132.183.28]:34432) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hages-0003Cv-5b for qemu-devel@nongnu.org; Tue, 11 Jun 2019 09:17:50 -0400 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 3D94A59474; Tue, 11 Jun 2019 13:17:39 +0000 (UTC) Received: from [10.72.12.214] (ovpn-12-214.pek2.redhat.com [10.72.12.214]) by smtp.corp.redhat.com (Postfix) with ESMTP id 8B23460DCA; Tue, 11 Jun 2019 13:17:34 +0000 (UTC) To: "Michael S. Tsirkin" , Like Xu References: <449c062f-373c-b310-ccc6-f14c702c8f19@linux.intel.com> <20190610114708-mutt-send-email-mst@kernel.org> From: Jason Wang Message-ID: <4c5a0454-865f-102e-94e5-6a38d011f33c@redhat.com> Date: Tue, 11 Jun 2019 21:17:32 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: <20190610114708-mutt-send-email-mst@kernel.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.39]); Tue, 11 Jun 2019 13:17:39 +0000 (UTC) Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [QUESTION] How to reduce network latency to improve netperf TCP_RR drastically? X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "qemu-devel@nongnu.org Developers" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 2019/6/10 =E4=B8=8B=E5=8D=8811:55, Michael S. Tsirkin wrote: > On Tue, Jun 04, 2019 at 03:10:43PM +0800, Like Xu wrote: >> Hi Michael=EF=BC=8C >> >> At https://www.linux-kvm.org/page/NetworkingTodo, there is an entry fo= r >> network latency saying: >> >> --- >> reduce networking latency: >> allow handling short packets from softirq or VCPU context >> Plan: >> We are going through the scheduler 3 times >> (could be up to 5 if softirqd is involved) >> Consider RX: host irq -> io thread -> VCPU thread -> >> guest irq -> guest thread. >> This adds a lot of latency. >> We can cut it by some 1.5x if we do a bit of work >> either in the VCPU or softirq context. >> Testing: netperf TCP RR - should be improved drastically >> netperf TCP STREAM guest to host - no regression >> Contact: MST >> --- >> >> I am trying to make some contributions to improving netperf TCP_RR. >> Could you please share more ideas or plans or implemental details to m= ake it >> happen? >> >> Thanks, >> Like Xu > > So some of this did happen. netif_receive_skb is now called > directly from tun_get_user. > > Question is about the rx/tun_put_user path now. > > If the vhost thread is idle, there's a single packet > outstanding then maybe we can forward the packet to userspace > directly from BH without waking up the thread. > > For this to work we need to map some userspace memory into kernel > ahead of the time. For example, maybe it can happen when > guest adds RX buffers? Copying Jason who's looking into > memory mapping matters. Btw, I wonder maybe it's time to make TODO wiki up to date. Thanks