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=-15.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=ham 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 EE8FEC433ED for ; Thu, 15 Apr 2021 11:34:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C8563611CD for ; Thu, 15 Apr 2021 11:34:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232375AbhDOLfN (ORCPT ); Thu, 15 Apr 2021 07:35:13 -0400 Received: from szxga05-in.huawei.com ([45.249.212.191]:17001 "EHLO szxga05-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230056AbhDOLfL (ORCPT ); Thu, 15 Apr 2021 07:35:11 -0400 Received: from DGGEMS405-HUB.china.huawei.com (unknown [172.30.72.59]) by szxga05-in.huawei.com (SkyGuard) with ESMTP id 4FLcck3HcWzPpxD; Thu, 15 Apr 2021 19:31:50 +0800 (CST) Received: from [10.174.187.224] (10.174.187.224) by DGGEMS405-HUB.china.huawei.com (10.3.19.205) with Microsoft SMTP Server id 14.3.498.0; Thu, 15 Apr 2021 19:34:40 +0800 Subject: Re: [PATCH 1/5] KVM: arm64: Divorce the perf code from oprofile helpers To: Marc Zyngier References: <20210414134409.1266357-1-maz@kernel.org> <20210414134409.1266357-2-maz@kernel.org> <87h7k7n81z.wl-maz@kernel.org> CC: , , , , , , Rich Felker , Yoshinori Sato , "Peter Zijlstra" , Viresh Kumar , Heiko Carstens , Arnaldo Carvalho de Melo , , Christian Borntraeger , , Will Deacon From: Keqian Zhu Message-ID: Date: Thu, 15 Apr 2021 19:34:40 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.7.1 MIME-Version: 1.0 In-Reply-To: <87h7k7n81z.wl-maz@kernel.org> Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.187.224] X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-sh@vger.kernel.org Hi Marc, On 2021/4/15 18:42, Marc Zyngier wrote: > On Thu, 15 Apr 2021 07:59:26 +0100, > Keqian Zhu wrote: >> >> Hi Marc, >> >> On 2021/4/14 21:44, Marc Zyngier wrote: >>> KVM/arm64 is the sole user of perf_num_counters(), and really >>> could do without it. Stop using the obsolete API by relying on >>> the existing probing code. >>> >>> Signed-off-by: Marc Zyngier >>> --- >>> arch/arm64/kvm/perf.c | 7 +------ >>> arch/arm64/kvm/pmu-emul.c | 2 +- >>> include/kvm/arm_pmu.h | 4 ++++ >>> 3 files changed, 6 insertions(+), 7 deletions(-) >>> >>> diff --git a/arch/arm64/kvm/perf.c b/arch/arm64/kvm/perf.c >>> index 739164324afe..b8b398670ef2 100644 >>> --- a/arch/arm64/kvm/perf.c >>> +++ b/arch/arm64/kvm/perf.c >>> @@ -50,12 +50,7 @@ static struct perf_guest_info_callbacks kvm_guest_cbs = { >>> >>> int kvm_perf_init(void) >>> { >>> - /* >>> - * Check if HW_PERF_EVENTS are supported by checking the number of >>> - * hardware performance counters. This could ensure the presence of >>> - * a physical PMU and CONFIG_PERF_EVENT is selected. >>> - */ >>> - if (IS_ENABLED(CONFIG_ARM_PMU) && perf_num_counters() > 0) >>> + if (kvm_pmu_probe_pmuver() != 0xf) >> The probe() function may be called many times >> (kvm_arm_pmu_v3_set_attr also calls it). I don't know whether the >> first calling is enough. If so, can we use a static variable in it, >> so the following calling can return the result right away? > > No, because that wouldn't help with crappy big-little implementations > that could have PMUs with different versions. We want to find the > version at the point where the virtual PMU is created, which is why we > call the probe function once per vcpu. I see. But AFAICS the pmuver is placed in kvm->arch, and the probe function is called once per VM. Maybe I miss something. > > This of course is broken in other ways (BL+KVM is a total disaster > when it comes to PMU), but making this static would just make it > worse. OK. Thanks, Keqian