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=-12.8 required=3.0 tests=BAYES_00,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, URIBL_BLOCKED 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 ED5A9C43463 for ; Sat, 19 Sep 2020 02:11:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 94C1F21707 for ; Sat, 19 Sep 2020 02:11:35 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="FzCBVfPx" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726192AbgISCLe (ORCPT ); Fri, 18 Sep 2020 22:11:34 -0400 Received: from us-smtp-1.mimecast.com ([205.139.110.61]:30146 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726054AbgISCLe (ORCPT ); Fri, 18 Sep 2020 22:11:34 -0400 X-Greylist: delayed 117635 seconds by postgrey-1.27 at vger.kernel.org; Fri, 18 Sep 2020 22:11:33 EDT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1600481492; 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=1fWqbBBRX5EVeWNpvGlaoHo5M6bYu8vy+AmYAkNS+X4=; b=FzCBVfPx7PTREl6RS+TjrQrnS99aRX5O/7r2fcG36xu+tAX0U0hoYJJSPheUJJ1S+lUP9d VhnXGEokT80Am+j09FFLcZHbpQuLnqLRwBIy1BYmnX49pbQrye3lGOJo7IozaZriLZOrWB p5zPWoLrOSNQQzXy4F62BzpJYXx59+I= 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-450-eSdF0UN0OC6HpK54gdFNUQ-1; Fri, 18 Sep 2020 22:11:30 -0400 X-MC-Unique: eSdF0UN0OC6HpK54gdFNUQ-1 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 mimecast-mx01.redhat.com (Postfix) with ESMTPS id 3F46E1074665; Sat, 19 Sep 2020 02:11:29 +0000 (UTC) Received: from x1.home (ovpn-112-71.phx2.redhat.com [10.3.112.71]) by smtp.corp.redhat.com (Postfix) with ESMTP id D5D6D60BF1; Sat, 19 Sep 2020 02:11:28 +0000 (UTC) Date: Fri, 18 Sep 2020 20:11:28 -0600 From: Alex Williamson To: Zenghui Yu Cc: Cornelia Huck , , , Subject: Re: [PATCH 2/2] vfio/pci: Remove bardirty from vfio_pci_device Message-ID: <20200918201128.16cf0a1c@x1.home> In-Reply-To: <3b5214f9-9e17-2bcd-1b92-57bacc1c1b31@huawei.com> References: <20200917033128.872-1-yuzenghui@huawei.com> <20200917033128.872-2-yuzenghui@huawei.com> <20200917133537.17af2ef3.cohuck@redhat.com> <20200917160742.4e4d6efd@x1.home> <3b5214f9-9e17-2bcd-1b92-57bacc1c1b31@huawei.com> Organization: Red Hat MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 19 Sep 2020 09:54:00 +0800 Zenghui Yu wrote: > Hi Alex, > > On 2020/9/18 6:07, Alex Williamson wrote: > > On Thu, 17 Sep 2020 13:35:37 +0200 > > Cornelia Huck wrote: > > > >> On Thu, 17 Sep 2020 11:31:28 +0800 > >> Zenghui Yu wrote: > >> > >>> It isn't clear what purpose the @bardirty serves. It might be used to avoid > >>> the unnecessary vfio_bar_fixup() invoking on a user-space BAR read, which > >>> is not required when bardirty is unset. > >>> > >>> The variable was introduced in commit 89e1f7d4c66d ("vfio: Add PCI device > >>> driver") but never actually used, so it shouldn't be that important. Remove > >>> it. > >>> > >>> Signed-off-by: Zenghui Yu > >>> --- > >>> drivers/vfio/pci/vfio_pci_config.c | 7 ------- > >>> drivers/vfio/pci/vfio_pci_private.h | 1 - > >>> 2 files changed, 8 deletions(-) > >> > >> Yes, it seems to have been write-only all the time. > > > > I suspect the intent was that vfio_bar_fixup() could test > > vdev->bardirty to avoid doing work if no BARs had been written since > > they were last read. As it is now we regenerate vconfig for all the > > BARs every time any offset of any of them are read. BARs aren't > > re-read regularly and config space is not a performance path, > > Yes, it seems that Qemu itself emulates all BAR registers and will read > the BAR from the kernel side only at initialization time. > > > but maybe > > we should instead test if we see any regressions from returning without > > doing any work in vfio_bar_fixup() if vdev->bardirty is false. Thanks, > > I will test it with the following diff. Please let me know which way do > you prefer. > > diff --git a/drivers/vfio/pci/vfio_pci_config.c > b/drivers/vfio/pci/vfio_pci_config.c > index d98843feddce..77c419d536d0 100644 > --- a/drivers/vfio/pci/vfio_pci_config.c > +++ b/drivers/vfio/pci/vfio_pci_config.c > @@ -515,7 +515,7 @@ static int vfio_basic_config_read(struct > vfio_pci_device *vdev, int pos, > int count, struct perm_bits *perm, > int offset, __le32 *val) > { > - if (is_bar(offset)) /* pos == offset for basic config */ > + if (is_bar(offset) && vdev->bardirty) /* pos == offset for basic > config */ > vfio_bar_fixup(vdev); > > count = vfio_default_config_read(vdev, pos, count, perm, > offset, val); There's only one caller currently, but I'd think it cleaner to put this in vfio_bar_fixup(), ie. return immediately if !bardirty. Thanks, Alex