From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id D6B6BC001B0 for ; Thu, 10 Aug 2023 01:19:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231771AbjHJBTZ (ORCPT ); Wed, 9 Aug 2023 21:19:25 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57684 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231196AbjHJBTY (ORCPT ); Wed, 9 Aug 2023 21:19:24 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E8BF910DC for ; Wed, 9 Aug 2023 18:18:36 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1691630316; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=8RyE1XhIfdOavy1+yd7tZWH6XrA0A0ZMjPep4bJOZxA=; b=A3Fsu839pyA4VM4uZIr6VXdbFy9Tg6/G7MicivBy0GbByahVspoYfXZVktHowrb9j405JF bRznq8M7/FLjDWq0dUJ9KkKaGmJsj13bCeUtWtR0raHZcU0BspREf8dEQ3jI71UPs/IJmO roWoTh640VGD1ngfffCac6YS/jrdVFY= Received: from mimecast-mx02.redhat.com (66.187.233.73 [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-251-yJgvA4ilMeOrCYwrgq4MeA-1; Wed, 09 Aug 2023 21:18:33 -0400 X-MC-Unique: yJgvA4ilMeOrCYwrgq4MeA-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 448DA1C04182; Thu, 10 Aug 2023 01:18:32 +0000 (UTC) Received: from localhost (unknown [10.72.112.99]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 45ECB2166B25; Thu, 10 Aug 2023 01:18:29 +0000 (UTC) Date: Thu, 10 Aug 2023 09:18:27 +0800 From: Baoquan He To: Ming Lei , mpe@ellerman.id.au, npiggin@gmail.com, christophe.leroy@csgroup.eu Cc: Christoph Hellwig , Jens Axboe , linux-nvme@lists.infradead.org, "Martin K . Petersen" , linux-scsi@vger.kernel.org, linux-block@vger.kernel.org, Wen Xiong , Keith Busch , linuxppc-dev@lists.ozlabs.org, Dave Young , kexec@lists.infradead.org, linux-kernel@vger.kernel.org, Pingfan Liu Subject: Re: [PATCH V3 01/14] blk-mq: add blk_mq_max_nr_hw_queues() Message-ID: References: <20230808104239.146085-1-ming.lei@redhat.com> <20230808104239.146085-2-ming.lei@redhat.com> <20230809134401.GA31852@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 3.1 on 10.11.54.6 Precedence: bulk List-ID: X-Mailing-List: linux-scsi@vger.kernel.org On 08/10/23 at 08:09am, Ming Lei wrote: > On Wed, Aug 09, 2023 at 03:44:01PM +0200, Christoph Hellwig wrote: > > I'm starting to sound like a broken record, but we can't just do random > > is_kdump checks, and it's not going to get better by resending it again and > > again. If kdump kernels limit the number of possible CPUs, it needs to > > reflected in cpu_possible_map and we need to use that information. > > > > Can you look at previous kdump/arch guys' comment about kdump usage & > num_possible_cpus? > > https://lore.kernel.org/linux-block/CAF+s44RuqswbosY9kMDx35crviQnxOeuvgNsuE75Bb0Y2Jg2uw@mail.gmail.com/ > https://lore.kernel.org/linux-block/ZKz912KyFQ7q9qwL@MiWiFi-R3L-srv/ > > The point is that kdump kernels does not limit the number of possible CPUs. > > 1) some archs support 'nr_cpus=1' for kdump kernel, which is fine, since > num_possible_cpus becomes 1. Yes, "nr_cpus=" is strongly suggested in kdump kernel because "nr_cpus=" limits the possible cpu numbers, while "maxcpuss=" only limits the cpu number which can be brought up during bootup. We noticed this diference because a large number of possible cpus will cost more memory in kdump kernel. e.g percpu initialization, even though kdump kernel have set "maxcpus=1". Currently x86 and arm64 all support "nr_cpus=". Pingfan ever spent much effort to make patches to add "nr_cpus=" support to ppc64, seems ppc64 dev and maintainers do not care about it. Finally the patches are not accepted, and the work is not continued. Now, I am wondering what is the barrier to add "nr_cpus=" to power ach. Can we reconsider adding 'nr_cpus=' to power arch since real issue occurred in kdump kernel? As for this patchset, it can be accpeted so that no failure in kdump kernel is seen on ARCHes w/o "nr_cpus=" support? My personal opinion. > > 2) some archs do not support 'nr_cpus=1', and have to rely on > 'max_cpus=1', so num_possible_cpus isn't changed, and kernel just boots > with single online cpu. That causes trouble because blk-mq limits single > queue. > > Documentation/admin-guide/kdump/kdump.rst > > Thanks, > Ming >