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 97468C4332F for ; Tue, 31 Oct 2023 13:49:50 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1qxp7P-0005WY-HK; Tue, 31 Oct 2023 09:49:19 -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 1qxp7O-0005Vt-Ai for qemu-devel@nongnu.org; Tue, 31 Oct 2023 09:49:18 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qxp7M-0007HW-FG for qemu-devel@nongnu.org; Tue, 31 Oct 2023 09:49:17 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1698760154; 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=4i99DJfkgIhPzdJU4QRsZ/OkV6XLN9AK7OBs5pamFbU=; b=hYnFaFOZwNIY6jVWDIdlToyHsGl8d7r4P7K8x002SZmd/3f4XUR6sxDvitzTXUwPnwKBSO CvWsSx+74X5T7Xut27hB3+DbC7JTTzBSrDXwDTk8PgGgnpVr8ooZIFhsIjT4mw8S++hFlX w4Q+5kbLIf4LL/3IYOg27J9W2WG291Q= 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-413-1HIB55WCPUu5qomvxRt-kA-1; Tue, 31 Oct 2023 09:48:58 -0400 X-MC-Unique: 1HIB55WCPUu5qomvxRt-kA-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (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 CA9B2104456A; Tue, 31 Oct 2023 13:48:57 +0000 (UTC) Received: from localhost (unknown [10.42.28.8]) by smtp.corp.redhat.com (Postfix) with ESMTP id 6FB651121308; Tue, 31 Oct 2023 13:48:57 +0000 (UTC) Date: Tue, 31 Oct 2023 13:48:56 +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: <20231031134856.GL7636@redhat.com> References: <20231017140150.44995-1-philmd@linaro.org> <20231017140150.44995-5-philmd@linaro.org> 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 10.11.54.3 Received-SPF: pass client-ip=170.10.129.124; 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_H4=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 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 Note that qemu has been compiled with QOM cast debug. This is the default for Fedora (not RHEL) because we'd like to get early detection of bugs from Fedora users. There was another patch recently where a simple change saved about 5% of total runtime in RISC-V TCG guests (admittedly a much more hot path than this one). https://lists.nongnu.org/archive/html/qemu-devel/2023-10/msg02388.html Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com Fedora Windows cross-compiler. Compile Windows programs, test, and build Windows installers. Over 100 libraries supported. http://fedoraproject.org/wiki/MinGW