Re: [PATCH V3 01/14] blk-mq: add blk_mq_max_nr_hw_queues()
From: Baoquan He <hidden>
Date: 2023-08-10 03:02:47
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kexec, linux-nvme, linux-scsi, linuxppc-dev, lkml
On 08/10/23 at 10:06am, Ming Lei wrote:
On Thu, Aug 10, 2023 at 09:18:27AM +0800, Baoquan He wrote:quoted
On 08/10/23 at 08:09am, Ming Lei wrote:quoted
On Wed, Aug 09, 2023 at 03:44:01PM +0200, Christoph Hellwig wrote:quoted
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/ (local) https://lore.kernel.org/linux-block/ZKz912KyFQ7q9qwL@MiWiFi-R3L-srv/ (local) 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.quoted
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.
Yes, 'nr_cpus=' is ideal. Not sure if there's some underlying concerns so that power people decided to not support it.