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 5398FD2AB15 for ; Wed, 30 Oct 2024 15:40:07 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1t6An7-0008Si-Rb; Wed, 30 Oct 2024 11:39:26 -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 1t6An5-0008SY-Rn for qemu-devel@nongnu.org; Wed, 30 Oct 2024 11:39:23 -0400 Received: from mgamail.intel.com ([192.198.163.14]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1t6An3-0004ET-H6 for qemu-devel@nongnu.org; Wed, 30 Oct 2024 11:39:23 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1730302761; x=1761838761; h=date:from:to:cc:subject:message-id:references: mime-version:content-transfer-encoding:in-reply-to; bh=Z2jAtlX+nm/qSFEmDG9JflN3eBD/+R6/qmApMimO224=; b=hgdr97+NriAShXnzcv5sJrC9qE9NkZSqps/yTIkE12ZWfpk7xorEPad4 n7w6VnvEJ6QCvzC/MJfRhWeRIWEdGdq64vsLfEAKV5UCnx9yKVu8579vA U4jYrHce6Lenw5psICsquIo2eXTewpYtujmMs6D/VruwO351NwPdXTwGT 5sKlUKcKlUBB2Hjj7OKa9w3g7hjDbSk3ppebAsp8FrzfJK1wY1V9mUmMG wrsZTLsL+kEG4qKLAo1QF85eVbnBU0MKL4kIKLoecZsGoBK93cnRTiElp bfbdMNKM4W6wc3XC5hjkEqAlx5HeDJvoChCS865yhr9S78VtBQJ1Qgs7y g==; X-CSE-ConnectionGUID: 1+BHHp0DRViqAGEDWM9JAA== X-CSE-MsgGUID: DYE1J2McQgiFVEdPkyRhGg== X-IronPort-AV: E=McAfee;i="6700,10204,11241"; a="30224597" X-IronPort-AV: E=Sophos;i="6.11,245,1725346800"; d="scan'208";a="30224597" Received: from orviesa004.jf.intel.com ([10.64.159.144]) by fmvoesa108.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 30 Oct 2024 08:39:16 -0700 X-CSE-ConnectionGUID: IY1MFOacR/imT59PApECfg== X-CSE-MsgGUID: /U8DLxNdTqmLtf+pVZs1fg== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.11,245,1725346800"; d="scan'208";a="87500440" Received: from liuzhao-optiplex-7080.sh.intel.com (HELO localhost) ([10.239.160.36]) by orviesa004.jf.intel.com with ESMTP; 30 Oct 2024 08:39:14 -0700 Date: Wed, 30 Oct 2024 23:55:34 +0800 From: Zhao Liu To: Tao Su 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=gb2312 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Received-SPF: pass client-ip=192.198.163.14; envelope-from=zhao1.liu@intel.com; helo=mgamail.intel.com X-Spam_score_int: -47 X-Spam_score: -4.8 X-Spam_bar: ---- X-Spam_report: (-4.8 / 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, 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 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 doesnĄ¯t exist, so using 0 is same > as -1Ą­ 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 donĄ¯t want to see -1, you can define a macro like APIC ID did (#define UNSET_AVX10_VERSION -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(). :) Thanks, Zhao