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 3B7DDC71130 for ; Tue, 10 Jun 2025 12:57:16 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1uOyXJ-0006bm-Ns; Tue, 10 Jun 2025 08:57:06 -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 1uOyXF-0006aD-IA for qemu-devel@nongnu.org; Tue, 10 Jun 2025 08:57:01 -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 1uOyX9-0002Zc-KW for qemu-devel@nongnu.org; Tue, 10 Jun 2025 08:57:01 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1749560213; h=from:from:reply-to: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=m5gsxmS3YBb/LFAIkUU/W0hMLRwggAnMdw0nJPa/0gI=; b=JspjpdtcA8qPLTFdxsuVrSTdOFN3LcAUbUwdr5FYUCI77eVU8OfwovwwyT6ji8Kl6bcnq4 qLWsdIRzGmM3zqn5dTDvEZTS+ueeRLJo8CjbSVpu7HJUa4mdA3zRAJDUYnpitU71OJAiVF lQ1itgJ0FmfMgBikwsbxMe0xkKlBI/A= Received: from mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-94-qcbrCAK2PBmpo-GPf6M7cA-1; Tue, 10 Jun 2025 08:56:50 -0400 X-MC-Unique: qcbrCAK2PBmpo-GPf6M7cA-1 X-Mimecast-MFC-AGG-ID: qcbrCAK2PBmpo-GPf6M7cA_1749560209 Received: from mx-prod-int-02.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-02.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.15]) (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 mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 2C98A19560B7; Tue, 10 Jun 2025 12:56:49 +0000 (UTC) Received: from redhat.com (unknown [10.42.28.87]) by mx-prod-int-02.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 9995A1956087; Tue, 10 Jun 2025 12:56:46 +0000 (UTC) Date: Tue, 10 Jun 2025 13:56:43 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= Cc: qemu-devel@nongnu.org, "Michael S. Tsirkin" , Peter Maydell , qemu-block@nongnu.org, Stefan Hajnoczi , Kevin Wolf Subject: Re: [PATCH 00/31] Skip automatic zero-init of large arrays / structs in I/O paths Message-ID: References: <20250610123709.835102-1-berrange@redhat.com> <50405e77-e665-4772-9715-3901730d00fd@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <50405e77-e665-4772-9715-3901730d00fd@linaro.org> User-Agent: Mutt/2.2.14 (2025-02-20) X-Scanned-By: MIMEDefang 3.0 on 10.30.177.15 Received-SPF: pass client-ip=170.10.133.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, 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_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 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: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= 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, Jun 10, 2025 at 02:49:02PM +0200, Philippe Mathieu-Daudé wrote: > On 10/6/25 14:36, Daniel P. Berrangé wrote: > > This series is an extension of Stefan's proposal: > > > > https://lists.nongnu.org/archive/html/qemu-devel/2025-06/msg00736.html > > > > It used '-Wframe-larger-than=4096' to identify all code locations > > with more than 4k on the stack. Any locations in the I/O paths > > were chosen to avoid automatic zero-init, to eliminate the performance > > overhead of the automatic initialization. > > Should we eventually add it to our default CFLAGS? You mean as a way to impose a hard limit on stack frame size ? FWIW, the VNC server is biggest at 100kb, but we have a large number of other big frames - here's a sorted list of frame sizes vs frequency 1 103696 2 69664 46 49184 4 42608 23 32880 23 32864 1 32832 1 28688 36 24800 10 24784 1 22240 21 21760 1 20624 1 17536 2 17168 1 16592 1 16576 1 16544 1 16512 2 16480 2 16464 1 16448 4 16432 1 15136 1 12960 1 12336 1 12048 1 10064 5 9184 1 8832 1 8784 1 8576 1 8448 2 8400 1 8384 2 8304 1 8272 4 8256 1 8240 4 8224 7 8208 2 7120 1 6800 1 5856 1 4928 2 4560 1 4464 1 4336 2 4256 1 4240 2 4224 4 4208 9 4176 9 4160 40 4144 68 4128 9 4112 With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|