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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6D9FCC433EF for ; Thu, 14 Oct 2021 08:28:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 453A360F36 for ; Thu, 14 Oct 2021 08:28:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230137AbhJNIaI (ORCPT ); Thu, 14 Oct 2021 04:30:08 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41592 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229994AbhJNIaG (ORCPT ); Thu, 14 Oct 2021 04:30:06 -0400 Received: from mail.skyhub.de (mail.skyhub.de [IPv6:2a01:4f8:190:11c2::b:1457]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 00731C061570 for ; Thu, 14 Oct 2021 01:28:01 -0700 (PDT) Received: from zn.tnic (p200300ec2f0c72004cd8e1678c0b16c3.dip0.t-ipconnect.de [IPv6:2003:ec:2f0c:7200:4cd8:e167:8c0b:16c3]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.skyhub.de (SuperMail on ZX Spectrum 128k) with ESMTPSA id 8FE331EC03EA; Thu, 14 Oct 2021 10:28:00 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=alien8.de; s=dkim; t=1634200080; 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:in-reply-to:in-reply-to: references:references; bh=+xlMsCTXETwM/qF1Rivq8W06GWg5T4rziG9VXU3Gh2E=; b=Hc6lZ/42+NquxuBUcHzIl2hPxgube6aDBEijG4v7jekL/7qqQa/QH2WwZXdyr4sVgriEfA bBFeqt92PFctlKIpvdemvTGjk0oLkYcaz9OOfDejbYgKSUcnAVoIrrE7GsZcHIQe7huf6k BkxHJZ9N15gSYIEMbBh3Xfo9nOMbrrQ= Date: Thu, 14 Oct 2021 10:28:00 +0200 From: Borislav Petkov To: Noah Goldstein Cc: tglx@linutronix.de, mingo@redhat.com, X86 ML , hpa@zytor.com, Andy Lutomirski , open list Subject: Re: [PATCH v1] x86/fpu: Remove opmask state from avx512_timestamp check Message-ID: References: <20210920053951.4093668-1-goldstein.w.n@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Oct 13, 2021 at 05:36:14PM -0500, Noah Goldstein wrote: > Ping2 Why? The original patch which added this abomination: 2f7726f95557 ("x86/fpu: Track AVX-512 usage of tasks") says already: the tracking mechanism is imprecise and can theoretically miss AVX-512 usage during context switch. But it has been measured to be precise enough to be useful under real-world workloads like tensorflow and linpack. If higher precision is required, suggest user space tools to use the PMU-based mechanisms in combination. and as you've noticed, the high 16 regs would cause a false positive too. So what is the actual real-life use case for this? -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette