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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id 24EB0C4332F for ; Tue, 31 Oct 2023 16:49:40 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1qxruw-0002bL-8B; Tue, 31 Oct 2023 12:48:38 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qxruu-0002bB-MT for qemu-devel@nongnu.org; Tue, 31 Oct 2023 12:48:36 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qxrut-0007YA-2h for qemu-devel@nongnu.org; Tue, 31 Oct 2023 12:48:36 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1698770914; 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=+oWPwECf4BfmrNUwJYzgG9ffP3wR+FR+QrPSCTN5HVI=; b=Wx4+nfpZrJsHC49iu8VNmK3B/2m1cVraJhs6vga4c2aNSJVgbhrpCtyyWWUIFkVJUO8xIT jw3BDX1eWZK1XkPhMSQXN41E5WRZ4EFC0YMkxGrr7rrMhQAIFzeHqhgUW3nvuUAdjh0gWT VwubSInuo1kbbpf1djJQpc2OKQ0ulqY= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-496-ucfNgkpoMJCtvjCnP_nbrQ-1; Tue, 31 Oct 2023 12:48:19 -0400 X-MC-Unique: ucfNgkpoMJCtvjCnP_nbrQ-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.rdu2.redhat.com [10.11.54.2]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 4F77C185A721; Tue, 31 Oct 2023 16:48:18 +0000 (UTC) Received: from localhost (unknown [10.42.28.8]) by smtp.corp.redhat.com (Postfix) with ESMTP id E86AC40C6EBC; Tue, 31 Oct 2023 16:48:17 +0000 (UTC) Date: Tue, 31 Oct 2023 16:48:17 +0000 From: "Richard W.M. Jones" To: Kevin Wolf Cc: Philippe =?iso-8859-1?Q?Mathieu-Daud=E9?= , qemu-devel@nongnu.org, Paolo Bonzini , Hanna Reitz , Fam Zheng , qemu-arm@nongnu.org, "Michael S. Tsirkin" , qemu-block@nongnu.org, Jason Wang , Peter Maydell , Raphael Norwitz , "Edgar E. Iglesias" , Alistair Francis , Gerd Hoffmann Subject: Re: [PATCH 4/7] hw/scsi/virtio-scsi: Use VIRTIO_SCSI_COMMON() macro Message-ID: <20231031164817.GN7636@redhat.com> References: <20231017140150.44995-1-philmd@linaro.org> <20231017140150.44995-5-philmd@linaro.org> <20231031134856.GL7636@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.2 Received-SPF: pass client-ip=170.10.133.124; envelope-from=rjones@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -25 X-Spam_score: -2.6 X-Spam_bar: -- X-Spam_report: (-2.6 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.481, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Tue, Oct 31, 2023 at 05:42:37PM +0100, Kevin Wolf wrote: > Am 31.10.2023 um 14:48 hat Richard W.M. Jones geschrieben: > > On Tue, Oct 31, 2023 at 02:17:56PM +0100, Kevin Wolf wrote: > > > Am 17.10.2023 um 16:01 hat Philippe Mathieu-Daudé geschrieben: > > > > Access QOM parent with the proper QOM VIRTIO_SCSI_COMMON() macro. > > > > > > > > Signed-off-by: Philippe Mathieu-Daudé > > > > --- > > > > hw/scsi/virtio-scsi.c | 2 +- > > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > > > diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c > > > > index 45b95ea070..fa53f0902c 100644 > > > > --- a/hw/scsi/virtio-scsi.c > > > > +++ b/hw/scsi/virtio-scsi.c > > > > @@ -761,7 +761,7 @@ static void virtio_scsi_fail_cmd_req(VirtIOSCSIReq *req) > > > > > > > > static int virtio_scsi_handle_cmd_req_prepare(VirtIOSCSI *s, VirtIOSCSIReq *req) > > > > { > > > > - VirtIOSCSICommon *vs = &s->parent_obj; > > > > + VirtIOSCSICommon *vs = VIRTIO_SCSI_COMMON(s); > > > > SCSIDevice *d; > > > > int rc; > > > > > > Why is a dynamic cast more "proper" than a static type-safe access, even > > > more so in a hot I/O path? > > > > > > Rich Jones posted a flamegraph the other day that surprised me because > > > object_class_dynamic_class_assert() and object_dynamic_cast_assert() > > > were shown to be a big part of scsi_req_new(). In the overall > > > performance, it's probably dwarved by other issues, but unnecessary > > > little things can add up, too. > > > > I think Kevin is referring to one of these flamegraphs: > > > > http://oirase.annexia.org/tmp/2023-kvm-build-on-device.svg > > http://oirase.annexia.org/tmp/2023-kvm-build.svg > > > > Here's a zoom showing scsi_req_new (hopefully this URL is stable ...): > > > > http://oirase.annexia.org/tmp/2023-kvm-build-on-device.svg?s=scsi_req_new&x=512.9&y=501 > > Oh, this one (kvm-build-on-device) doesn't even show the object cast. > I was looking at kvm-build, it seems, where both the class and the > object cast are visible: > > http://oirase.annexia.org/tmp/2023-kvm-build.svg?s=scsi_req_new&x=455.4&y=533 Not sure if this is the reason why, but the difference between these two runs is that kvm-build is backed by a qcow2 file and kvm-build-on-device is backed by a host block device. I believe they both were otherwise identically configured qemu. More background in this Fedora thread: https://lists.fedoraproject.org/archives/list/devel@lists.fedoraproject.org/thread/MSJAL7OE2TBO6U4ZWXKTKQLDSGRFK6YR/ Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com virt-p2v converts physical machines to virtual machines. Boot with a live CD or over the network (PXE) and turn machines into KVM guests. http://libguestfs.org/virt-v2v