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 AB81FE68953 for ; Thu, 31 Oct 2024 04:45:51 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1t6N3O-0001yO-S4; Thu, 31 Oct 2024 00:45:03 -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 1t6N3M-0001xt-J6 for qemu-devel@nongnu.org; Thu, 31 Oct 2024 00:45:00 -0400 Received: from mgamail.intel.com ([198.175.65.15]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1t6N3J-0000HE-Cz for qemu-devel@nongnu.org; Thu, 31 Oct 2024 00:45:00 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1730349898; x=1761885898; h=date:from:to:cc:subject:message-id:references: mime-version:content-transfer-encoding:in-reply-to; bh=HRCmAZnWLGDrm4bikgE5sZyFS7uzA9BWSNmBIVUMsKU=; b=OeT/yWipnGs+jzyehXGrsBAObxZAI1XJe1csd83tYTEK5gCvuj54BtKk /5rKSs57v25A6a9PJuDxgyJvlB2DQ+qcEdbIR1VABAlwebka7ZiBItcGl yN66Tnz7Wk2CjjuA/nFX+2c0CPhl633qrIJhPx5vyf9+GXh5/x1NAtyhM 2KY6CVukFMOiKRd+Z8uxs7pbQNDFxaEygBkT2bA7LCkDRO2Y9aTzXxUSV 774yCyNVLxoXswXNwBgfncDYb/dPVR5e6pL6PzdK9t9Vxi1Hx6gk8wVBm 7AlITcfGti3aCxyZy9IfNm08QC6ZAOr2S/EUm5tMseRm5GC0g/Z7vUogz Q==; X-CSE-ConnectionGUID: wnVEp4vTSnmC9MRFw07DEA== X-CSE-MsgGUID: Yi6N2sG0TXOIMRzbMg/9/A== X-IronPort-AV: E=McAfee;i="6700,10204,11222"; a="33767357" X-IronPort-AV: E=Sophos;i="6.11,199,1725346800"; d="scan'208";a="33767357" Received: from fmviesa001.fm.intel.com ([10.60.135.141]) by orvoesa107.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 30 Oct 2024 21:44:46 -0700 X-CSE-ConnectionGUID: RTM2PlljTZer3m4r80BP1w== X-CSE-MsgGUID: eGFlQGv5SheqCLdpQUQ3XA== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.11,246,1725346800"; d="scan'208";a="113375182" Received: from linux.bj.intel.com ([10.238.157.71]) by smtpauth.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 30 Oct 2024 21:44:41 -0700 Date: Thu, 31 Oct 2024 12:39:31 +0800 From: Tao Su To: Zhao Liu Cc: Paolo Bonzini , qemu-devel@nongnu.org, xiaoyao.li@intel.com Subject: Re: [PATCH 4/8] target/i386: add AVX10 feature and AVX10 version property Message-ID: References: <20241029151858.550269-1-pbonzini@redhat.com> <20241029151858.550269-5-pbonzini@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Received-SPF: none client-ip=198.175.65.15; envelope-from=tao1.su@linux.intel.com; helo=mgamail.intel.com X-Spam_score_int: -46 X-Spam_score: -4.7 X-Spam_bar: ---- X-Spam_report: (-4.7 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.366, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_MED=-2.3, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, SPF_HELO_NONE=0.001, SPF_NONE=0.001 autolearn=ham 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 Wed, Oct 30, 2024 at 11:55:34PM +0800, Zhao Liu wrote: > On Wed, Oct 30, 2024 at 10:05:51PM +0800, Tao Su wrote: > > Date: Wed, 30 Oct 2024 22:05:51 +0800 > > From: Tao Su > > Subject: Re: [PATCH 4/8] target/i386: add AVX10 feature and AVX10 version > > property > > > > On Wed, Oct 30, 2024 at 09:21:36PM +0800, Zhao Liu wrote: > > > > > > Introduce avx10-version property so that avx10 version can be controlled > > > > > > by user and cpu model. Per spec, avx10 version can never be 0, the default > > > > > > value of avx10-version is set to 0 to determine whether it is specified by > > > > > > user. > > > > > > > > > > The default value of 0 does not reflect whether the user has set it to 0. > > > > > According to the description here, the spec clearly prohibits 0, so > > > > > should we report an error when the user sets it to 0? > > > > > > > > > > If so, it might be better to change the default value to -1 and adjust > > > > > based on the host's support. > > > > > > > > > > > > > If user sets version to 0, it will directly use reported version, this > > > > should be a more neat and intuitive way? > > > > > > The code implementation is actually similar for different initial > > > values. And about this: > > > > > > > If user sets version to 0, it will directly use reported version", > > > > > > It's defining a special behavior for the API, which is based on the > > > special 0 value, and there needs to be documentation to let the user > > > know that 0 will be considered legal as well as that it will be quietly > > > overridden... But AFAIK there doesn't seem to be any place to add > > > documentation for the property ... > > > > > > There may be similar problems with -1, e.g. if the user writes -1, there > > > is no way to report an error for the user's behavior. But it's better > > > than 0. After all, no one would think that a version of -1 is correct. > > > Topology IDs have been initialized to -1 to include the user's 0 value > > > in the check. > > > > Thanks for your explanation, but I really think the users who set > > avx10-version should also know avx10.0 doesn’t exist, so using 0 is same > > as -1… > > I see. "Per spec, avx10 version can never be 0", so showing the warning > for avx10-version=0 is as it should be. > > > To solve the initial value issue fundamentally, maybe we can add get/set > > callbacks when adding avx10-version property? It should be simpler to > > limit what users set. > > It's unnecessary. Similar cases using -1 are already common, such as for > APIC ID, NUMA node ID, topology IDs, etc. The initial value is -1 simply > because we need to handle the case where users explicitly set it to 0. > If you don’t want to see -1, you can define a macro like APIC ID did > (#define UNSET_AVX10_VERSION -1). > OK, I will change the default value to -1. > > > > > @@ -7674,13 +7682,21 @@ static bool x86_cpu_filter_features(X86CPU *cpu, bool verbose) > > > > > &eax_0, &ebx_0, &ecx_0, &edx_0); > > > > > uint8_t version = ebx_0 & 0xff; > > > > > > > > > > - if (version < env->avx10_version) { > > > > > + if (!env->avx10_version) { > > > > > + env->avx10_version = version; > > > > > > > > x86_cpu_filter_features() is not a good place to assign avx10_version, I > > > > still tend to set it in max_x86_cpu_realize(). > > > > > > It's not proper to get the host's version when AVX10 cannot be enabled, > > > even maybe host doesn't support AVX10. > > > > > > As you found out earlier, max_x86_cpu_realize doesn't know if AVX10 can > > > be enabled or not. > > > > > > > How about moving to x86_cpu_expand_features()? We can set when checking > > cpu->max_features. > > The feature bit set in x86_cpu_expand_features() is unstable since it > may be masked later in x86_cpu_filter_features(). :) > A lot of feature bits are set in x86_cpu_expand_features() with reported value, so I think avx10_version can also be set to reported value there. I mainly want to let avx10_version be assigned only when -cpu host or max, so that it can be distinguished from the cpu model. This should also be Paolo's original intention in v2.