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Thu, 15 Apr 2021 13:49:37 +0000 Received: from disco-boy.misterjones.org (disco-boy.misterjones.org [51.254.78.96]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 8E051613C3; Thu, 15 Apr 2021 13:49:33 +0000 (UTC) Received: from 78.163-31-62.static.virginmediabusiness.co.uk ([62.31.163.78] helo=why.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94) (envelope-from ) id 1lX2N9-007ekc-H0; Thu, 15 Apr 2021 14:49:31 +0100 Date: Thu, 15 Apr 2021 14:49:30 +0100 Message-ID: <87czuvmzdh.wl-maz@kernel.org> From: Marc Zyngier To: Keqian Zhu Cc: , , , , , , Rich Felker , Yoshinori Sato , "Peter\ Zijlstra" , Viresh Kumar , Heiko Carstens , Arnaldo Carvalho de Melo , , Christian Borntraeger , , Will Deacon Subject: Re: [PATCH 1/5] KVM: arm64: Divorce the perf code from oprofile helpers In-Reply-To: References: <20210414134409.1266357-1-maz@kernel.org> <20210414134409.1266357-2-maz@kernel.org> <87h7k7n81z.wl-maz@kernel.org> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/27.1 (x86_64-pc-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") X-SA-Exim-Connect-IP: 62.31.163.78 X-SA-Exim-Rcpt-To: zhukeqian1@huawei.com, kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, dalias@libc.org, ysato@users.sourceforge.jp, peterz@infradead.org, viresh.kumar@linaro.org, hca@linux.ibm.com, acme@kernel.org, nathan@kernel.org, borntraeger@de.ibm.com, kernel-team@android.com, will@kernel.org X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210415_064933_935939_84466645 X-CRM114-Status: GOOD ( 31.00 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, 15 Apr 2021 12:34:40 +0100, Keqian Zhu wrote: > > 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. You're right, I mis-remembered. This doesn't change much though. Thanks, M. -- Without deviation from the norm, progress is not possible. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel