On 08/10/23 at 10:06am, Ming Lei wrote: > 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@xxxxxxxxxxxxxx/ > > > 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. Yes, 'nr_cpus=' is ideal. Not sure if there's some underlying concerns so that power people decided to not support it.
