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=-0.9 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,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 F3EE8C65BAE for ; Thu, 13 Dec 2018 20:12:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BAF9420851 for ; Thu, 13 Dec 2018 20:12:32 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org BAF9420851 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727481AbeLMUMb (ORCPT ); Thu, 13 Dec 2018 15:12:31 -0500 Received: from mx1.redhat.com ([209.132.183.28]:45256 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726435AbeLMUMb (ORCPT ); Thu, 13 Dec 2018 15:12:31 -0500 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 34C663082138; Thu, 13 Dec 2018 20:12:31 +0000 (UTC) Received: from redhat.com (ovpn-120-21.rdu2.redhat.com [10.10.120.21]) by smtp.corp.redhat.com (Postfix) with SMTP id 14BB560BE7; Thu, 13 Dec 2018 20:12:29 +0000 (UTC) Date: Thu, 13 Dec 2018 15:12:29 -0500 From: "Michael S. Tsirkin" To: Jason Wang Cc: kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH net-next 0/3] vhost: accelerate metadata access through vmap() Message-ID: <20181213144116-mutt-send-email-mst@kernel.org> References: <20181213101022.12475-1-jasowang@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181213101022.12475-1-jasowang@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.42]); Thu, 13 Dec 2018 20:12:31 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Dec 13, 2018 at 06:10:19PM +0800, Jason Wang wrote: > Hi: > > This series tries to access virtqueue metadata through kernel virtual > address instead of copy_user() friends since they had too much > overheads like checks, spec barriers or even hardware feature > toggling. > > Test shows about 24% improvement on TX PPS. It should benefit other > cases as well. > > Please review I think the idea of speeding up userspace access is a good one. However I think that moving all checks to start is way too aggressive. Instead, let's batch things up but let's not keep them around forever. Here are some ideas: 1. Disable preemption, process a small number of small packets directly in an atomic context. This should cut latency down significantly, the tricky part is to only do it on a light load and disable this for the streaming case otherwise it's unfair. This might fail, if it does just bounce things out to a thread. 2. Switch to unsafe_put_user/unsafe_get_user, and batch up multiple accesses. 3. Allow adding a fixup point manually, such that multiple independent get_user accesses can get a single fixup (will allow better compiler optimizations). > Jason Wang (3): > vhost: generalize adding used elem > vhost: fine grain userspace memory accessors > vhost: access vq metadata through kernel virtual address > > drivers/vhost/vhost.c | 281 ++++++++++++++++++++++++++++++++++++++---- > drivers/vhost/vhost.h | 11 ++ > 2 files changed, 266 insertions(+), 26 deletions(-) > > -- > 2.17.1