From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965518AbeBMSYB (ORCPT ); Tue, 13 Feb 2018 13:24:01 -0500 Received: from merlin.infradead.org ([205.233.59.134]:35266 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965217AbeBMSYA (ORCPT ); Tue, 13 Feb 2018 13:24:00 -0500 Date: Tue, 13 Feb 2018 19:23:51 +0100 From: Peter Zijlstra To: Raghavendra Rao Ananta Cc: mingo@redhat.com, acme@kernel.org, alexander.shishkin@linux.intel.com, jolsa@redhat.com, namhyung@kernel.org, linux-kernel@vger.kernel.org, psodagud@codeaurora.org, tsoni@codeaurora.org Subject: Re: [PATCH] perf: Add support for creating offline events Message-ID: <20180213182351.GQ25201@hirez.programming.kicks-ass.net> References: <1518217620-28458-1-git-send-email-rananta@codeaurora.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1518217620-28458-1-git-send-email-rananta@codeaurora.org> User-Agent: Mutt/1.9.2 (2017-12-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Feb 09, 2018 at 03:07:00PM -0800, Raghavendra Rao Ananta wrote: > Perf framework doesn't allow creation of hardware events if > the requested CPU is offline. However, creation of an event > is achievable if the event is attached to the PMU as soon > as the CPU is online again. > > So, introducing a feature that could allow to create events > even when the CPU is offline and return a success to the caller. > If, during the time of event creation, the CPU is found offline, > the event is moved to a new state (PERF_EVENT_STATE_DORMANT). As > and when the CPU is know to be woken up (through hotplug notifiers), > all the dormant events would be attached to the PMU (by > perf_install_in_context()). If during the life time of the event, > the CPU hasn't come online, the dormant event would just be freed. This is horrible.. and you seem to have forgotten to explain why you care about offline CPUs.