Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754113AbaJUArS (ORCPT ); Mon, 20 Oct 2014 20:47:18 -0400 Received: from mx0a-0016f401.pphosted.com ([67.231.148.174]:20070 "EHLO mx0a-0016f401.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753038AbaJUArP (ORCPT ); Mon, 20 Oct 2014 20:47:15 -0400 From: Neil Zhang To: Dan Streetman CC: Greg KH , "linux-kernel@vger.kernel.org" Date: Mon, 20 Oct 2014 17:47:09 -0700 Subject: RE: [PATCH] drivers: base: update cpu offline info when do hotplug Thread-Topic: [PATCH] drivers: base: update cpu offline info when do hotplug Thread-Index: Ac/sh7aCR8NyL9U0QrWhIyu5ivXqegAQLhTg Message-ID: <9034CBD80F070943B59700D7F8149ED9024EB81D3A@SC-VEXCH4.marvell.com> References: <1413775748-22478-1-git-send-email-zhangwm@marvell.com> <20141020044340.GA9589@kroah.com> <9034CBD80F070943B59700D7F8149ED9024EB81CAF@SC-VEXCH4.marvell.com> <20141020064826.GA4064@kroah.com> <9034CBD80F070943B59700D7F8149ED9024EB81CC6@SC-VEXCH4.marvell.com> In-Reply-To: Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: acceptlanguage: en-US Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:5.12.52,1.0.28,0.0.0000 definitions=2014-10-20_05:2014-10-20,2014-10-20,1970-01-01 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=7.0.1-1402240000 definitions=main-1410210007 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from base64 to 8bit by nfs id s9L0lMV0028108 Dan, > -----Original Message----- > From: ddstreet@gmail.com [mailto:ddstreet@gmail.com] On Behalf Of Dan > Streetman > Sent: 2014年10月21日 1:03 > To: Neil Zhang > Cc: Greg KH; linux-kernel@vger.kernel.org > Subject: Re: [PATCH] drivers: base: update cpu offline info when do > hotplug > > On Mon, Oct 20, 2014 at 3:40 AM, Neil Zhang wrote: > > Greg, > > > > > > -----Original Message----- > > From: Greg KH [mailto:gregkh@linuxfoundation.org] > > Sent: 2014年10月20日 14:48 > > To: Neil Zhang > > Cc: linux-kernel@vger.kernel.org > > Subject: Re: [PATCH] drivers: base: update cpu offline info when do > > hotplug > > > > On Sun, Oct 19, 2014 at 11:39:23PM -0700, Neil Zhang wrote: > >>> How much noise is this going to cause on a big/little system that > >>> constantly hot unplug/plugs processors all of the time? > >> > >> Can you explain more what kind of noise will be introduced on a > big/little system? > > > > Have you tested this on such a machine? > > > > I didn't have such kind of machine on hand. > > Can anyone has such machine to verify it? > > Thanks! > > I tested this on a ppc PowerVM system, using dlpar operations to > remove/add cpus. > > Without this patch the cpu online nodes get out of sync with the main > online node (and the actual state of the cpus), because they aren't > updated as the cpus are brought up/down: > > [root@br10p02 cpu]$ pwd > /sys/devices/system/cpu > [root@br10p02 cpu]$ cat online > 0-39 > [root@br10p02 cpu]$ for n in {0..47} ; do test $( cat cpu$n/online ) - > eq 1 && echo -n "$n " ; done ; echo "" > 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 > 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 > > > While with the patch, the cpu online nodes are kept up to date as the > cpus are brought up/down: > > [root@br10p02 cpu]$ pwd > /sys/devices/system/cpu > [root@br10p02 cpu]$ cat online > 0-39 > [root@br10p02 cpu]$ for n in {0..47} ; do test $( cat cpu$n/online ) - > eq 1 && echo -n "$n " ; done ; echo "" > 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 > 27 28 29 30 31 32 33 34 35 36 37 38 39 > > > Feel free to add Thanks for your kindly test! > > Tested-by: Dan Streetman > > > > >> As I know IKS on arm will use cpu_suspend way to power down a core. > > > > Are you sure that it also doesn't use that same functionality to drop > a processor to save power? > > > > As I know it use cpu_suspend to switch out a processor in IKS and > there is no cpu hotplug notifier in this procedure. > > > > > > Why do you need/want this notification? What are you going to do > with this information that you don't already have? > > > > The offline won't be updated if an in kernel hotplug governor plug in > / out a core which cause the sysfs interface report a wrong status. > > > > > > thanks, > > > > greg k-h > > > > > > Best Regards, > > Neil Zhang Best Regards, Neil Zhang ????{.n?+???????+%?????ݶ??w??{.n?+????{??G?????{ay?ʇڙ?,j??f???h?????????z_??(?階?ݢj"???m??????G????????????&???~???iO???z??v?^?m???? ????????I?