From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754667AbeBNIcS (ORCPT ); Wed, 14 Feb 2018 03:32:18 -0500 Received: from bombadil.infradead.org ([198.137.202.133]:35316 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754492AbeBNIcR (ORCPT ); Wed, 14 Feb 2018 03:32:17 -0500 Date: Wed, 14 Feb 2018 09:32:13 +0100 From: Peter Zijlstra To: Sodagudi Prasad Cc: Raghavendra Rao Ananta , mingo@redhat.com, acme@kernel.org, alexander.shishkin@linux.intel.com, jolsa@redhat.com, namhyung@kernel.org, linux-kernel@vger.kernel.org, tsoni@codeaurora.org Subject: Re: [PATCH] perf: Add support for creating offline events Message-ID: <20180214083213.GS25181@hirez.programming.kicks-ass.net> References: <1518217620-28458-1-git-send-email-rananta@codeaurora.org> <20180213182351.GQ25201@hirez.programming.kicks-ass.net> <7d3d97fafa654c30b4ca776180760cb3@codeaurora.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <7d3d97fafa654c30b4ca776180760cb3@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 Tue, Feb 13, 2018 at 02:17:07PM -0800, Sodagudi Prasad wrote: > > This is horrible.. and you seem to have forgotten to explain why you > > care about offline CPUs. > > Up to 4.9 kernel, drivers can register cpu hotplug notfiters and drivers are > able to create perf events dynamically based cpu notifies callback events. > As cpu hot plug is converted to state machine approach from hot plug > notifiers, every driver need to define a cpuhp state and registers with cpu > hotplug state machine for creating perf events dynamically. > > Qualcomm have use cases to monitor the cpu cycles and other hw events > continuously on all cpus from kernel and profiling tools. > So we are thinking that there could be other soc vendors, who are interested > in perf events preserving across cpu hot plug and perf events creation on > hot plugged cores. But _why_ are you hotplugging to begin with? Just don't do that.