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[209.132.180.67]) by mx.google.com with ESMTP id w9si13538459otl.138.2020.01.16.07.38.43; Thu, 16 Jan 2020 07:38:56 -0800 (PST) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; dkim=pass header.i=@redhat.com header.s=mimecast20190719 header.b=dN4qqa3u; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726883AbgAPPhn (ORCPT + 99 others); Thu, 16 Jan 2020 10:37:43 -0500 Received: from us-smtp-2.mimecast.com ([207.211.31.81]:43869 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726744AbgAPPhm (ORCPT ); Thu, 16 Jan 2020 10:37:42 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1579189061; 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=rxATJWJ4rcj/wFapXV73v8XDh+PJUvOaeSFeG4RlODo=; b=dN4qqa3u9nEQ01SHGpEwgDoTqMONFWWOlFt7TXpAA99e28tFbagsw3vac/ojAqiN3QJr8i nPSTDx2W75IAhOBdNkJ+0EX5Hw6NFH0ZH70YK6exOndyIo7/1mxi3Tnv5aOy1pWyRUPWdv +94/vdjWsIQiO4c/dqnqi1NtaEjhzKc= 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-105-46WynO7RPH-Cvo2cy4apiw-1; Thu, 16 Jan 2020 10:37:37 -0500 X-MC-Unique: 46WynO7RPH-Cvo2cy4apiw-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 7A0C386A063; Thu, 16 Jan 2020 15:37:36 +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 44B9166D22; Thu, 16 Jan 2020 15:37:30 +0000 (UTC) Date: Thu, 16 Jan 2020 08:37:29 -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" , "Tian, Kevin" , "peterx@redhat.com" Subject: Re: [PATCH v2 2/2] drm/i915/gvt: subsitute kvm_read/write_guest with vfio_dma_rw Message-ID: <20200116083729.40983f38@w520.home> In-Reply-To: <20200116054941.GB1759@joy-OptiPlex-7040> References: <20200115034132.2753-1-yan.y.zhao@intel.com> <20200115035455.12417-1-yan.y.zhao@intel.com> <20200115130651.29d7e9e0@w520.home> <20200116054941.GB1759@joy-OptiPlex-7040> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 16 Jan 2020 00:49:41 -0500 Yan Zhao wrote: > On Thu, Jan 16, 2020 at 04:06:51AM +0800, Alex Williamson wrote: > > 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? > > > I only tested the 4 interfaces in GVT's environment, where most of the > guest memory accesses are less than one page. > And the different fluctuations should be caused by the locks. > vfio_dma_rw contends locks with other vfio accesses which are assumed to > be abundant in the case of GVT. Hmm, so maybe it's time to convert vfio_iommu.lock from a mutex to a rwsem? Thanks, Alex > > > 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); > > > oh, it seems that I missed Paolo's mail. will change it. thank you! > > Thanks > Yan > > > > > } > > >