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 824AEE68956 for ; Thu, 31 Oct 2024 05:53:27 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1t6O6o-00063u-9t; Thu, 31 Oct 2024 01:52:38 -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 1t6O6n-00063g-3y for qemu-devel@nongnu.org; Thu, 31 Oct 2024 01:52:37 -0400 Received: from mgamail.intel.com ([198.175.65.19]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1t6O6j-00083y-GP for qemu-devel@nongnu.org; Thu, 31 Oct 2024 01:52:36 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1730353954; x=1761889954; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=jizHZ6rmOL9AHYI/XATRS+FMMsEXfizs6jIzulXdqgI=; b=UoD2YGWMrUh7zO9O5X2+OJdnQlF0gi6gvK0XZKSKxK7ONhRNR3s2erhp 0zEtTkAk25+v0FMn0Ewot9780UvyKcqqH1S5fbwo5/ajjTIjBcI85oYLg WXycC8X/XGqA9FQwHcPYpymno5Rb8MvfSJ75HAjdJJKcpwvtmRCj6YI7F Pi2500m9WQawt93mbImCspv7CS+nHSt9gQI2cZ72fnRCKhIkGTX7ShuZy Fvt5LHM8kggwGSJahV0hWJzIZKDXXQne0UHPuiEW4LtpYvZMJoq+GhPMl yGaoPAAgykcvJu2sYHju2snNbKL0Hm6QQAfMnkorPU/2zpGPEQo6VtJ2E A==; X-CSE-ConnectionGUID: oB7/1FyuTGST5vR809tFhw== X-CSE-MsgGUID: 3uIWuMlQRIGXtJaddsOicw== X-IronPort-AV: E=McAfee;i="6700,10204,11222"; a="29936899" X-IronPort-AV: E=Sophos;i="6.11,199,1725346800"; d="scan'208";a="29936899" Received: from fmviesa010.fm.intel.com ([10.60.135.150]) by orvoesa111.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 30 Oct 2024 22:52:29 -0700 X-CSE-ConnectionGUID: URTDY0dXTrOgoDjflpHVAQ== X-CSE-MsgGUID: Gm8nXrXaS3WjzjhnBTfRjA== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.11,247,1725346800"; d="scan'208";a="82846250" Received: from xiaoyaol-hp-g830.ccr.corp.intel.com (HELO [10.124.227.172]) ([10.124.227.172]) by fmviesa010-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 30 Oct 2024 22:52:27 -0700 Message-ID: <92635403-e483-45a8-afcd-0e8fa5080f23@intel.com> Date: Thu, 31 Oct 2024 13:52:24 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 4/8] target/i386: add AVX10 feature and AVX10 version property To: Tao Su , Zhao Liu Cc: Paolo Bonzini , qemu-devel@nongnu.org References: <20241029151858.550269-1-pbonzini@redhat.com> <20241029151858.550269-5-pbonzini@redhat.com> Content-Language: en-US From: Xiaoyao Li In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=198.175.65.19; envelope-from=xiaoyao.li@intel.com; helo=mgamail.intel.com X-Spam_score_int: -39 X-Spam_score: -4.0 X-Spam_bar: ---- X-Spam_report: (-4.0 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.366, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, HK_RANDOM_ENVFROM=0.001, HK_RANDOM_FROM=0.781, 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_PASS=-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 10/31/2024 12:39 PM, Tao Su wrote: > 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. Then please remember to handle the issue like ... >>>>>> @@ -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 agree. > 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. avx10_version needs to be assigned with a default valid value, when user enables avx10 explicitly without specifying avx10_version. It also applies to (existing) named cpu models other than GraniteRapids-v2 (which is added by this series). E.g., -cpu GraniteRapids-v1,+avx10 So if you are going to make default value as -1, then you need to add something in x86_cpu_load_model() if (!def->avx10_version) { def->avx10_version = -1; }