From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751425AbdEAQKp (ORCPT ); Mon, 1 May 2017 12:10:45 -0400 Received: from mail-by2nam01on0042.outbound.protection.outlook.com ([104.47.34.42]:3776 "EHLO NAM01-BY2-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1750986AbdEAQKe (ORCPT ); Mon, 1 May 2017 12:10:34 -0400 Authentication-Results: arm.com; dkim=none (message not signed) header.d=none;arm.com; dmarc=none action=none header.from=caviumnetworks.com; Date: Mon, 1 May 2017 16:10:19 +0000 From: Jayachandran C To: Will Deacon Cc: "Pinski, Andrew" , "Jayachandran C." , Ganapatrao Kulkarni , Mark Rutland , Catalin Marinas , "linux-kernel@vger.kernel.org" , "acme@kernel.org" , "alexander.shishkin@linux.intel.com" , "peterz@infradead.org" , Ingo Molnar , "Nair, Jayachandran" , "Kulkarni, Ganapatrao" , "linux-arm-kernel@lists.infradead.org" Subject: Re: [PATCH v2] arm64: perf: Use only exclude_kernel attribute when kernel is running in HYP Message-ID: <20170501161018.GA7112@localhost> References: <20170424154530.GO12323@arm.com> <20170425165259.GS24484@arm.com> <20170426101021.GF21744@arm.com> <20170426134141.GA6417@localhost> <20170427173758.GN1890@arm.com> <20170428134623.GA85316@localhost> <20170428163823.GX13675@arm.com> MIME-Version: 1.0 Content-Type: text/plain; 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Ignoring the exclude_hv if > > > > it cannot be honored would be a better solution. > > > > > > Better for HHVM, sure, but I don't think it's better in general. It means > > > that we silently do the opposite of what the user has requested in some > > > configurations. > > > > If my understanding is correct, when is_kernel_in_hyp_mode() is true, > > the kernel is in EL2 and there is no real hypervisor with hvc calls > > from kernel. Ignoring the exclude_hv would be correct. > > > > When kernel is in EL1, it would be correct to consider exclude_hv to > > skip events in EL2 (reached with hvc). > > > > I don't see the issue, can you please give more detail on the config > > with unexpected behavior? > > This got me thinking, so I tried to look at the history of exclude_hv. It > turns out it was added in 0475f9ea8e2c ("perf_counters: allow users to > count user, kernel and/or hypervisor events") for PowerPC, not x86 (where > this doesn't seem to be supported). > > Notably, it looks like it's always ignored for the x86 CPU PMU, and ignored > on PowerPC when a hypervisor is not present. I think that backs up your > suggestion that we should ignore it when is_kernel_in_hyp_mode() is true. > > In which case, I withdraw my objection to ignoring exclude_hv when running > in hyp mode, but please add a comment explaining the rationale! Thanks, we will send out an updated patch with a commit message summarizing this disucssion. JC