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 X-Spam-Level: X-Spam-Status: No, score=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A2D77C433DB for ; Fri, 15 Jan 2021 15:13:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7055623884 for ; Fri, 15 Jan 2021 15:13:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732429AbhAOPNN (ORCPT ); Fri, 15 Jan 2021 10:13:13 -0500 Received: from mga06.intel.com ([134.134.136.31]:40521 "EHLO mga06.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727719AbhAOPNM (ORCPT ); Fri, 15 Jan 2021 10:13:12 -0500 IronPort-SDR: 9hF5RDPqv+L5bMA891vlFdV1fpVpa/68mjZnTywI/vkMgxqv6b8jFaGDsU9G66fgj3QLXXyCj8 Z2gYKW5PqVyA== X-IronPort-AV: E=McAfee;i="6000,8403,9864"; a="240104676" X-IronPort-AV: E=Sophos;i="5.79,349,1602572400"; d="scan'208";a="240104676" Received: from orsmga008.jf.intel.com ([10.7.209.65]) by orsmga104.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 15 Jan 2021 07:12:32 -0800 IronPort-SDR: YMRvbCJfBgNMtsfli4winv39sw8mvETNYSyyFo7Vc/HVBypP1QY3aFIOoXdd4lvX71KuFz+uVO 5Uam87Dptpag== X-IronPort-AV: E=Sophos;i="5.79,349,1602572400"; d="scan'208";a="382694568" Received: from likexu-mobl1.ccr.corp.intel.com (HELO [10.249.174.174]) ([10.249.174.174]) by orsmga008-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 15 Jan 2021 07:12:28 -0800 Subject: Re: [PATCH v3 04/17] perf: x86/ds: Handle guest PEBS overflow PMI and inject it to guest To: Peter Zijlstra Cc: Like Xu , Kan Liang , Paolo Bonzini , eranian@google.com, kvm@vger.kernel.org, Ingo Molnar , Sean Christopherson , Thomas Gleixner , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Andi Kleen , wei.w.wang@intel.com, luwei.kang@intel.com, linux-kernel@vger.kernel.org References: <20210104131542.495413-1-like.xu@linux.intel.com> <20210104131542.495413-5-like.xu@linux.intel.com> <9c343e40-bbdf-8af0-3307-5274070ee3d2@intel.com> <2c197d5a-09a8-968c-a942-c95d18983c9d@intel.com> From: "Xu, Like" Message-ID: <18715b60-9510-566d-f533-d722d50145d1@intel.com> Date: Fri, 15 Jan 2021 23:12:25 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.6.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On 2021/1/15 22:44, Peter Zijlstra wrote: > On Fri, Jan 15, 2021 at 10:30:13PM +0800, Xu, Like wrote: > >>> Are you sure? Spurious NMI/PMIs are known to happen anyway. We have far >>> too much code to deal with them. >> https://lore.kernel.org/lkml/20170628130748.GI5981@leverpostej/T/ >> >> In the rr workload, the commit change "the PMI interrupts in skid region >> should be dropped" >> is reverted since some users complain that: >> >>> It seems to me that it might be reasonable to ignore the interrupt if >>> the purpose of the interrupt is to trigger sampling of the CPUs >>> register state. But if the interrupt will trigger some other >>> operation, such as a signal on an fd, then there's no reason to drop >>> it. >> I assume that if the PMI drop is unacceptable, either will spurious PMI >> injection. >> >> I'm pretty open if you insist that we really need to do this for guest PEBS >> enabling. > That was an entirely different issue. We were dropping events on the > floor because they'd passed priv boundaries. So there was an actual > event, and we made it go away. Thanks for your clarification and support. > What we're talking about here is raising an PMI with BUFFER_OVF set, > even if the DS is empty. That should really be harmless. We'll take the > PMI, find there's nothing there, and do nothing. The only harm point is confusing the guest PEBS user with the behavior of pebs_interrupt_threshold. Now that KVM has to break it due to cross-mapping issue, Let me implement this idea in the next version w/ relevant performance data.