From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933698AbcI0LqI (ORCPT ); Tue, 27 Sep 2016 07:46:08 -0400 Received: from mx1.redhat.com ([209.132.183.28]:43948 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752768AbcI0Lp7 (ORCPT ); Tue, 27 Sep 2016 07:45:59 -0400 Message-ID: <57EA5BF4.1060508@redhat.com> Date: Tue, 27 Sep 2016 07:45:56 -0400 From: Prarit Bhargava User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 MIME-Version: 1.0 To: Borislav Petkov CC: linux-kernel@vger.kernel.org, Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , x86@kernel.org, Greg Kroah-Hartman , Peter Zijlstra , Len Brown , Andi Kleen , Jiri Olsa , Juergen Gross Subject: Re: [PATCH 0/2 v3] cpu hotplug: Preserve topology directory after soft remove event References: <1474457973-19536-1-git-send-email-prarit@redhat.com> <20160921130428.2e7bprll64vs6h2r@pd.tnic> <57E28BFF.8060107@redhat.com> <20160921140135.i5emid4qno2o6cre@pd.tnic> <57E3C78C.5040400@redhat.com> <20160922121039.l6lnhb53os2af27x@pd.tnic> <57E90A61.60402@redhat.com> <20160926115728.sdnvjaz3ty6xpsvr@pd.tnic> In-Reply-To: <20160926115728.sdnvjaz3ty6xpsvr@pd.tnic> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.26]); Tue, 27 Sep 2016 11:45:58 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/26/2016 07:57 AM, Borislav Petkov wrote: > On Mon, Sep 26, 2016 at 07:45:37AM -0400, Prarit Bhargava wrote: >> When offline, /sys/devices/system/cpuX/cpu/online is 0. The problem is that >> when online is 0, topology disappears so there is no way to determine _the >> location_ of the offline'd thread. > > What does "the location" mean exactly? > >> cpupower should still print out all asterisks for down'd threads. It does not >> because the topology directory is incorrectly removed. >> >> IOW how does userspace know the _location_ of the thread? The topology >> directory no longer exists when the thread is downed, so core_id and >> physical_package_id (both of which would be effectively static) do not exist. >> The whole point of this patchset is to know where the offline'd thread actually is. > > What do you mean "where"? The socket and core location. Look at it this way (and let's get the terminology straight at the same time). You have a socket CPU. That socket has cores on it. Each core (at least on Intel) has two threads. I down a thread (as you did): > > $ echo 0 > /sys/devices/system/cpu/cpu2/online This results in the topology directory being destroyed. It shouldn't be -- the socket and core are still there. If you could open up your computer you could touch them. This is similar to downing a PCI device, or removing !kernel memory DIMM from a system. The device is still physically there. > $ cat /sys/devices/system/cpu/online > 0-1,3-7 > > So core 2 is right between 1 and 3. Yes. But *where* is it relative to the cores and socket(s)? > > If you need to show the package id, you still iterate over the core > numbers in an increasing order and show '*' for the offlined ones. > Explain this in more detail please? P.