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 448B5C001E0 for ; Thu, 10 Aug 2023 02:07:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230124AbjHJCH5 (ORCPT ); Wed, 9 Aug 2023 22:07:57 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44980 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229503AbjHJCH4 (ORCPT ); Wed, 9 Aug 2023 22:07:56 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 77AC81FCC for ; Wed, 9 Aug 2023 19:07:04 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1691633223; 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=CujbJvk8xR2wivezZL312pI5YeFGQCWJwDhrju025js=; b=FNu8aQbjfleXY52kOe3p62/xWSJ9qs4ILHg6ob3apVde1gJO6HeL2Ey/nkmSRCDjC+T5z3 Jm8V+sOABUHioBHcTbZXE2/gGoAFleT/GF1ybYJko+bSzGSCz9ZjqDunrzY1VTmpSGeeeR VPvfbF47y7Ld8jdRyqB833JDgkKrlms= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-376-02XBssC6PbqWp0BJ03OIxQ-1; Wed, 09 Aug 2023 22:07:00 -0400 X-MC-Unique: 02XBssC6PbqWp0BJ03OIxQ-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.rdu2.redhat.com [10.11.54.1]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 822FB185A78F; Thu, 10 Aug 2023 02:06:59 +0000 (UTC) Received: from fedora (unknown [10.72.120.5]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 16AB540C2076; Thu, 10 Aug 2023 02:06:50 +0000 (UTC) Date: Thu, 10 Aug 2023 10:06:46 +0800 From: Ming Lei To: Baoquan He Cc: mpe@ellerman.id.au, npiggin@gmail.com, christophe.leroy@csgroup.eu, 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 10.11.54.1 Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Thu, Aug 10, 2023 at 09:18:27AM +0800, Baoquan He wrote: > 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? If 'nr_cpus=' can be supported on ppc64, this patchset isn't needed. > > 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. IMO 'nr_cpus=' support should be preferred, given it is annoying to maintain two kinds of implementation for kdump kernel from driver viewpoint. I guess kdump things can be simplified too with supporting 'nr_cpus=' only. thanks, Ming