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=-6.9 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,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 E3FEEC32771 for ; Wed, 15 Jan 2020 20:06:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B967122522 for ; Wed, 15 Jan 2020 20:06:56 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="BR3QDKZ4" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729818AbgAOUG4 (ORCPT ); Wed, 15 Jan 2020 15:06:56 -0500 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:42819 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1729794AbgAOUGz (ORCPT ); Wed, 15 Jan 2020 15:06:55 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1579118814; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=ouETeL4IvzIbfGB9Fv8qtP6i/4HZznlTaT1Dbkur2g8=; b=BR3QDKZ4vGb0G79avssm4n9uzKTcjp0FqB6mICd+27iKD0N31PpfifbpbYzGuHOlrX3Z7k CUJVr72vt0pcSmFY0VRg5ui6i3QRkY14FT1PHTJcw3d08MRm3Am48HCk66hKzb+iyJ2xIN oUaGyN5osk6YqMLMdjrUbROnVZk54qw= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-316-Y5nQ-SI0N2iGLdeInMhekQ-1; Wed, 15 Jan 2020 15:06:53 -0500 X-MC-Unique: Y5nQ-SI0N2iGLdeInMhekQ-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 1FAD01005510; Wed, 15 Jan 2020 20:06:52 +0000 (UTC) Received: from w520.home (ovpn-116-28.phx2.redhat.com [10.3.116.28]) by smtp.corp.redhat.com (Postfix) with ESMTP id 8BD99675AF; Wed, 15 Jan 2020 20:06:51 +0000 (UTC) Date: Wed, 15 Jan 2020 13:06:51 -0700 From: Alex Williamson To: Yan Zhao Cc: zhenyuw@linux.intel.com, intel-gvt-dev@lists.freedesktop.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, pbonzini@redhat.com, kevin.tian@intel.com, peterx@redhat.com Subject: Re: [PATCH v2 2/2] drm/i915/gvt: subsitute kvm_read/write_guest with vfio_dma_rw Message-ID: <20200115130651.29d7e9e0@w520.home> In-Reply-To: <20200115035455.12417-1-yan.y.zhao@intel.com> References: <20200115034132.2753-1-yan.y.zhao@intel.com> <20200115035455.12417-1-yan.y.zhao@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 14 Jan 2020 22:54:55 -0500 Yan Zhao wrote: > As a device model, it is better to read/write guest memory using vfio > interface, so that vfio is able to maintain dirty info of device IOVAs. > > Compared to kvm interfaces kvm_read/write_guest(), vfio_dma_rw() has ~600 > cycles more overhead on average. > > ------------------------------------- > | interface | avg cpu cycles | > |-----------------------------------| > | kvm_write_guest | 1554 | > | ----------------------------------| > | kvm_read_guest | 707 | > |-----------------------------------| > | vfio_dma_rw(w) | 2274 | > |-----------------------------------| > | vfio_dma_rw(r) | 1378 | > ------------------------------------- In v1 you had: ------------------------------------- | interface | avg cpu cycles | |-----------------------------------| | kvm_write_guest | 1546 | | ----------------------------------| | kvm_read_guest | 686 | |-----------------------------------| | vfio_iova_rw(w) | 2233 | |-----------------------------------| | vfio_iova_rw(r) | 1262 | ------------------------------------- So the kvm numbers remained within +0.5-3% while the vfio numbers are now +1.8-9.2%. I would have expected the algorithm change to at least not be worse for small accesses and be better for accesses crossing page boundaries. Do you know what happened? > Comparison of benchmarks scores are as blow: > ------------------------------------------------------ > | avg score | kvm_read/write_guest | vfio_dma_rw | > |----------------------------------------------------| > | Glmark2 | 1284 | 1296 | > |----------------------------------------------------| > | Lightsmark | 61.24 | 61.27 | > |----------------------------------------------------| > | OpenArena | 140.9 | 137.4 | > |----------------------------------------------------| > | Heaven | 671 | 670 | > ------------------------------------------------------ > No obvious performance downgrade found. > > Cc: Kevin Tian > Signed-off-by: Yan Zhao > --- > drivers/gpu/drm/i915/gvt/kvmgt.c | 26 +++++++------------------- > 1 file changed, 7 insertions(+), 19 deletions(-) > > diff --git a/drivers/gpu/drm/i915/gvt/kvmgt.c b/drivers/gpu/drm/i915/gvt/kvmgt.c > index bd79a9718cc7..17edc9a7ff05 100644 > --- a/drivers/gpu/drm/i915/gvt/kvmgt.c > +++ b/drivers/gpu/drm/i915/gvt/kvmgt.c > @@ -1966,31 +1966,19 @@ static int kvmgt_rw_gpa(unsigned long handle, unsigned long gpa, > void *buf, unsigned long len, bool write) > { > struct kvmgt_guest_info *info; > - struct kvm *kvm; > - int idx, ret; > - bool kthread = current->mm == NULL; > + int ret; > + struct intel_vgpu *vgpu; > + struct device *dev; > > if (!handle_valid(handle)) > return -ESRCH; > > info = (struct kvmgt_guest_info *)handle; > - kvm = info->kvm; > - > - if (kthread) { > - if (!mmget_not_zero(kvm->mm)) > - return -EFAULT; > - use_mm(kvm->mm); > - } > - > - idx = srcu_read_lock(&kvm->srcu); > - ret = write ? kvm_write_guest(kvm, gpa, buf, len) : > - kvm_read_guest(kvm, gpa, buf, len); > - srcu_read_unlock(&kvm->srcu, idx); > + vgpu = info->vgpu; > + dev = mdev_dev(vgpu->vdev.mdev); > > - if (kthread) { > - unuse_mm(kvm->mm); > - mmput(kvm->mm); > - } > + ret = write ? vfio_dma_rw(dev, gpa, buf, len, true) : > + vfio_dma_rw(dev, gpa, buf, len, false); As Paolo suggested previously, this can be simplified: ret = vfio_dma_rw(dev, gpa, buf, len, write); > > return ret; Or even more simple, remove the ret variable: return vfio_dma_rw(dev, gpa, buf, len, write); Thanks, Alex > }