From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755037AbcHBH4F (ORCPT ); Tue, 2 Aug 2016 03:56:05 -0400 Received: from mx1.redhat.com ([209.132.183.28]:43822 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751640AbcHBHz6 (ORCPT ); Tue, 2 Aug 2016 03:55:58 -0400 Date: Tue, 2 Aug 2016 15:46:02 +0800 From: Baoquan He To: Zhou Wenjian Cc: linux-kernel@vger.kernel.org, kexec@lists.infradead.org, dyoung@redhat.com, d.hatayama@jp.fujitsu.com Subject: Re: [PATCH v2] Documentation: kdump: add description of bringing up SMP dump-capture kernel Message-ID: <20160802074602.GA3663@x1.redhat.com> References: <1470010988-18050-1-git-send-email-zhouwj-fnst@cn.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1470010988-18050-1-git-send-email-zhouwj-fnst@cn.fujitsu.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.38]); Tue, 02 Aug 2016 07:46:09 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Wenjian, On 08/01/16 at 08:23am, Zhou Wenjian wrote: > v1->v2: change nr_cpus to maxcpus > > SMP dump-capture kernel is useful to improve the performance of kdump in > some cases. So add the description of bringing up SMP dump-capture kernel. > > Signed-off-by: Zhou Wenjian Discussed with people, it could be better to adjust the description about nr_cpus and maxcpus part. I think you can still describe nr_cpus/maxcpus in patch 1/2, and keep parallel dumping part in 2/2. Originally maxcpus=1 is used for all ARCHes. Later people found nr_cpus=1 is better since nr_cpus decides the number of possible cpu while maxcpus decides the max working cpu after system boot. So nr_cpus can save memory because percpu will pre-allocate memory for each possible cpu for hotplug. So on x86 nr_cpus is used because much memory can be saved if possible cpu number is very large. So you can mention that both maxcpus and nr_cpus can be used but nr_cpus has advantage if it has been implemented in some ARCHes like x86_64. And I guess you mush have tested parallel dumping feature with nr_cpus specified, it makes sense to tell people with the real situation. Thanks Baoquan > --- > Documentation/kdump/kdump.txt | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/Documentation/kdump/kdump.txt b/Documentation/kdump/kdump.txt > index 88ff63d..c5762b7 100644 > --- a/Documentation/kdump/kdump.txt > +++ b/Documentation/kdump/kdump.txt > @@ -394,6 +394,12 @@ Notes on loading the dump-capture kernel: > dump. Hence generally it is useful either to build a UP dump-capture > kernel or specify maxcpus=1 option while loading dump-capture kernel. > > +* We should bring up a SMP dump-capture kernel if we intend to use multi-threads > + programs with it, such as parallel dump feature of makedumpfile. Otherwise, > + the multi-threads program may have a great performance degradation. > + To bring up a SMP dump-capture kernel, we should specify maxcpus=[X] and > + disable_cpu_apic=[Y] options while loading it. > + > * For s390x there are two kdump modes: If a ELF header is specified with > the elfcorehdr= kernel parameter, it is used by the kdump kernel as it > is done on all other architectures. If no elfcorehdr= kernel parameter is > -- > 1.8.3.1 > > > From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mx1.redhat.com ([209.132.183.28]) by bombadil.infradead.org with esmtps (Exim 4.85_2 #1 (Red Hat Linux)) id 1bUUPG-0002Sz-Pm for kexec@lists.infradead.org; Tue, 02 Aug 2016 07:46:31 +0000 Date: Tue, 2 Aug 2016 15:46:02 +0800 From: Baoquan He Subject: Re: [PATCH v2] Documentation: kdump: add description of bringing up SMP dump-capture kernel Message-ID: <20160802074602.GA3663@x1.redhat.com> References: <1470010988-18050-1-git-send-email-zhouwj-fnst@cn.fujitsu.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <1470010988-18050-1-git-send-email-zhouwj-fnst@cn.fujitsu.com> List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "kexec" Errors-To: kexec-bounces+dwmw2=infradead.org@lists.infradead.org To: Zhou Wenjian Cc: dyoung@redhat.com, d.hatayama@jp.fujitsu.com, kexec@lists.infradead.org, linux-kernel@vger.kernel.org Hi Wenjian, On 08/01/16 at 08:23am, Zhou Wenjian wrote: > v1->v2: change nr_cpus to maxcpus > > SMP dump-capture kernel is useful to improve the performance of kdump in > some cases. So add the description of bringing up SMP dump-capture kernel. > > Signed-off-by: Zhou Wenjian Discussed with people, it could be better to adjust the description about nr_cpus and maxcpus part. I think you can still describe nr_cpus/maxcpus in patch 1/2, and keep parallel dumping part in 2/2. Originally maxcpus=1 is used for all ARCHes. Later people found nr_cpus=1 is better since nr_cpus decides the number of possible cpu while maxcpus decides the max working cpu after system boot. So nr_cpus can save memory because percpu will pre-allocate memory for each possible cpu for hotplug. So on x86 nr_cpus is used because much memory can be saved if possible cpu number is very large. So you can mention that both maxcpus and nr_cpus can be used but nr_cpus has advantage if it has been implemented in some ARCHes like x86_64. And I guess you mush have tested parallel dumping feature with nr_cpus specified, it makes sense to tell people with the real situation. Thanks Baoquan > --- > Documentation/kdump/kdump.txt | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/Documentation/kdump/kdump.txt b/Documentation/kdump/kdump.txt > index 88ff63d..c5762b7 100644 > --- a/Documentation/kdump/kdump.txt > +++ b/Documentation/kdump/kdump.txt > @@ -394,6 +394,12 @@ Notes on loading the dump-capture kernel: > dump. Hence generally it is useful either to build a UP dump-capture > kernel or specify maxcpus=1 option while loading dump-capture kernel. > > +* We should bring up a SMP dump-capture kernel if we intend to use multi-threads > + programs with it, such as parallel dump feature of makedumpfile. Otherwise, > + the multi-threads program may have a great performance degradation. > + To bring up a SMP dump-capture kernel, we should specify maxcpus=[X] and > + disable_cpu_apic=[Y] options while loading it. > + > * For s390x there are two kdump modes: If a ELF header is specified with > the elfcorehdr= kernel parameter, it is used by the kdump kernel as it > is done on all other architectures. If no elfcorehdr= kernel parameter is > -- > 1.8.3.1 > > > _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec