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=-6.6 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 A0D46C433DF for ; Thu, 20 Aug 2020 03:32:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 804CE20639 for ; Thu, 20 Aug 2020 03:32:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726862AbgHTDcp (ORCPT ); Wed, 19 Aug 2020 23:32:45 -0400 Received: from mga06.intel.com ([134.134.136.31]:60344 "EHLO mga06.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726698AbgHTDcn (ORCPT ); Wed, 19 Aug 2020 23:32:43 -0400 IronPort-SDR: 4SRboyQGcOy9J7mluKLMzczxS02sZUQlSlNLLRBDGjDXHIzvYu23P5G52r8kXlfr3FxHtFVHcW RMfPKjWDdmDg== X-IronPort-AV: E=McAfee;i="6000,8403,9718"; a="216765273" X-IronPort-AV: E=Sophos;i="5.76,332,1592895600"; d="scan'208";a="216765273" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga005.jf.intel.com ([10.7.209.41]) by orsmga104.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 19 Aug 2020 20:32:42 -0700 IronPort-SDR: axVaO01PiEwdrsY0XR0Zs3O9fWoXIXfcdqJr+2+0OrOhS2gTJz67WfqAXaLG9BdFPh2R/m8ouo ZkY7Asw5Ghhg== X-IronPort-AV: E=Sophos;i="5.76,332,1592895600"; d="scan'208";a="472477121" Received: from likexu-mobl1.ccr.corp.intel.com (HELO [10.238.4.128]) ([10.238.4.128]) by orsmga005-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 19 Aug 2020 20:32:36 -0700 Subject: Re: [PATCH v1 01/11] perf/x86/core: Support KVM to assign a dedicated counter for guest PEBS To: Peter Zijlstra , "Paolo Bonzini (KVM Super Maintainer)" Cc: "Kang, Luwei" , "Liang, Kan" , "x86@kernel.org" , "linux-kernel@vger.kernel.org" , "kvm@vger.kernel.org" , "mingo@redhat.com" , "acme@kernel.org" , "mark.rutland@arm.com" , "alexander.shishkin@linux.intel.com" , "jolsa@redhat.com" , "namhyung@kernel.org" , "tglx@linutronix.de" , "bp@alien8.de" , "hpa@zytor.com" , "pbonzini@redhat.com" , "Christopherson, Sean J" , "vkuznets@redhat.com" , "wanpengli@tencent.com" , "jmattson@google.com" , "joro@8bytes.org" , "pawan.kumar.gupta@linux.intel.com" , "ak@linux.intel.com" , "thomas.lendacky@amd.com" , "Yu, Fenghua" , "Wang, Wei W" , "Kleen, Andi" References: <1583431025-19802-1-git-send-email-luwei.kang@intel.com> <1583431025-19802-2-git-send-email-luwei.kang@intel.com> <20200306135317.GD12561@hirez.programming.kicks-ass.net> <20200309100443.GG12561@hirez.programming.kicks-ass.net> <97ce1ba4-d75a-8db2-ea2f-7d334942b4e6@linux.intel.com> <20200309150526.GI12561@hirez.programming.kicks-ass.net> From: Like Xu Organization: Intel OTC Message-ID: <34cb1d8c-d7c0-0dc1-49b2-072147f37379@linux.intel.com> Date: Thu, 20 Aug 2020 11:32:32 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Peter, On 2020/6/12 13:28, Kang, Luwei wrote: >>>> Suppose your KVM thing claims counter 0/2 (ICL/SKL) for some random >>>> PEBS event, and then the host wants to use PREC_DIST.. Then one of >>>> them will be screwed for no reason what so ever. >>>> >>> >>> The multiplexing should be triggered. >>> >>> For host, if both user A and user B requires PREC_DIST, the >>> multiplexing should be triggered for them. >>> Now, the user B is KVM. I don't think there is difference. The >>> multiplexing should still be triggered. Why it is screwed? >> >> Becuase if KVM isn't PREC_DIST we should be able to reschedule it to a >> different counter. >> >>>> How is that not destroying scheduling freedom? Any other situation >>>> we'd have moved the !PREC_DIST PEBS event to another counter. >>>> >>> >>> All counters are equivalent for them. It doesn't matter if we move it >>> to another counter. There is no impact for the user. >> >> But we cannot move it to another counter, because you're pinning it. > > Hi Peter, > > To avoid the pinning counters, I have tried to do some evaluation about > patching the PEBS record for guest in KVM. In this approach, about ~30% > time increased on guest PEBS PMI handler latency ( > e.g.perf record -e branch-loads:p -c 1000 ~/Tools/br_instr a). > > Some implementation details as below: > 1. Patching the guest PEBS records "Applicable Counters" filed when the guest > required counter is not the same with the host. Because the guest PEBS > driver will drop these PEBS records if the "Applicable Counters" not the > same with the required counter index. > 2. Traping the guest driver's behavior(VM-exit) of disabling PEBS. > It happens before reading PEBS records (e.g. PEBS PMI handler, before > application exit and so on) > 3. To patch the Guest PEBS records in KVM, we need to get the HPA of the > guest PEBS buffer. > <1> Trapping the guest write of IA32_DS_AREA register and get the GVA > of guest DS_AREA. > <2> Translate the DS AREA GVA to GPA(kvm_mmu_gva_to_gpa_read) > and get the GVA of guest PEBS buffer from DS AREA > (kvm_vcpu_read_guest_atomic). > <3> Although we have got the GVA of PEBS buffer, we need to do the > address translation(GVA->GPA->HPA) for each page. Because we can't > assume the GPAs of Guest PEBS buffer are always continuous. > > But we met another issue about the PEBS counter reset field in DS AREA. > pebs_event_reset in DS area has to be set for auto reload, which is per > counter. Guest and Host may use different counters. Let's say guest wants to > use counter 0, but host assign counter 1 to guest. Guest sets the reset value to > pebs_event_reset[0]. However, since counter 1 is the one which is eventually > scheduled, HW will use pebs_event_reset[1] as reset value. > > We can't copy the value of the guest pebs_event_reset[0] to > pebs_event_reset[1] directly(Patching DS AREA) because the guest driver may > confused, and we can't assume the guest counter 0 and 1 are not used for this > PEBS task at the same time. And what's more, KVM can't aware the guest > read/write to the DS AREA because it just a general memory for guest. > > What is your opinion or do you have a better proposal? Do we have any update or clear attitude on this "patching the PEBS record for guest in KVM" proposal ？ Thanks, Like Xu > > Thanks, > Luwei Kang > >> >>> In the new proposal, KVM user is treated the same as other host events >>> with event constraint. The scheduler is free to choose whether or not >>> to assign a counter for it. >> >> That's what it does, I understand that. I'm saying that that is creating artificial >> contention. >> >> >> Why is this needed anyway? Can't we force the guest to flush and then move it >> over to a new counter?