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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 22BE5C48BD5 for ; Tue, 25 Jun 2019 13:30:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 02F9F214DA for ; Tue, 25 Jun 2019 13:30:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730260AbfFYNaA (ORCPT ); Tue, 25 Jun 2019 09:30:00 -0400 Received: from foss.arm.com ([217.140.110.172]:42026 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726506AbfFYN37 (ORCPT ); Tue, 25 Jun 2019 09:29:59 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 0E1FC2B; Tue, 25 Jun 2019 06:29:59 -0700 (PDT) Received: from [10.1.196.120] (e121650-lin.cambridge.arm.com [10.1.196.120]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id DCCE93F718; Tue, 25 Jun 2019 06:29:57 -0700 (PDT) Subject: Re: [PATCH 3/7] perf: arm64: Use rseq to test userspace access to pmu counters To: Mark Rutland , will.deacon@arm.com Cc: Arnaldo Carvalho de Melo , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, mingo@redhat.com, peterz@infradead.org, catalin.marinas@arm.com, mathieu.desnoyers@efficios.com References: <20190611125315.18736-1-raphael.gault@arm.com> <20190611125315.18736-4-raphael.gault@arm.com> <20190611143346.GB28689@kernel.org> <20190611165755.GG29008@lakrids.cambridge.arm.com> From: Raphael Gault Message-ID: Date: Tue, 25 Jun 2019 14:29:56 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: <20190611165755.GG29008@lakrids.cambridge.arm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Mark, Hi Will, Now that we have a better idea what enabling this feature for heterogeneous systems would look like (both with or without using rseqs), it might be worth discussing if this is in fact a desirable thing in term of performance-complexity trade off. Indeed, while not as scary as first thought, maybe the rseq method would still dissuade users from using this feature. It is also worth noting that if we only enable this feature on homogeneous system, the `mrs` hook/emulation would not be necessary. If because of the complexity of the setup we need to consider whether we want to upstream this and have to maintain it afterward. Thanks, -- Raphael Gault