On 07/11/23 at 11:53am, Ming Lei wrote: > Hi Baoquan, > > On Tue, Jul 11, 2023 at 11:35:50AM +0800, Baoquan He wrote: > > On 07/10/23 at 05:14pm, Ming Lei wrote: > > > On Mon, Jul 10, 2023 at 08:41:09AM +0200, Christoph Hellwig wrote: > > > > On Sat, Jul 08, 2023 at 10:02:59AM +0800, Ming Lei wrote: > > > > > Take blk-mq's knowledge into account for calculating io queues. > > > > > > > > > > Fix wrong queue mapping in case of kdump kernel. > > > > > > > > > > On arm and ppc64, 'maxcpus=1' is passed to kdump command line, see > > > > > `Documentation/admin-guide/kdump/kdump.rst`, so num_possible_cpus() > > > > > still returns all CPUs. > > > > > > > > That's simply broken. Please fix the arch code to make sure > > > > it does not return a bogus num_possible_cpus value for these > > > > > > That is documented in Documentation/admin-guide/kdump/kdump.rst. > > > > > > On arm and ppc64, 'maxcpus=1' is passed for kdump kernel, and "maxcpu=1" > > > simply keep one of CPU cores as online, and others as offline. > > > > I don't know maxcpus on arm and ppc64 well. But maxcpus=1 or nr_cpus=1 > > are suggested parameter. Because usually nr_cpus=1 is enough to make > > kdump kernel work well to capture vmcore. However, user is allowed to > > specify nr_cpus=n (n>1) if they think multiple cpus are needed in kdump > > kernel. Your hard coding of cpu number in kdump kernel may be not so > > reasonable. > > As I mentioned, for arm/ppc64, passing 'maxcpus=1' actually follows > Documentation/admin-guide/kdump/kdump.rst. > > 'nr_cpus=N' just works fine, so not related with this topic. > > After 'maxcpus=1' is passed, kernel only brings up one of cpu cores as > online during booting, and others still can be put into online by > userspace. Now this way causes IO timeout on some storage device which > uses managed irq and supports multiple io queues. > > Here the focus is if passing 'maxcpus=1' is valid for kdump > kernel, that is we want to hear from our arch/kdump guys. Yes, 'maxcpus=1' is valid and suggested on ppc64 for kdump kernel if needed, because there's no 'nr_cpus=' support on ppc64 yet. > > If yes, something needs to be fixed, such as, what this patchset is > doing. > > > > > Please cc kexec mailing list when posting so that people can view the > > whole thread of discussion. > > Already Cc kexe & arm/powerpc & irq list. > > > Thanks, > Ming >
