Re: [PATCH 2/2] nvme-pci: use blk_mq_max_nr_hw_queues() to calculate io queues

[Keith Busch]

On Mon, Jul 10, 2023 at 05:14:15PM +0800, 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.
> 
> So Cc our arch(arm & ppc64) & kdump guys wrt. passing 'maxcpus=1' for
> kdump kernel.
> 
> > setups, otherwise you'll have to paper over it in all kind of
> > drivers.
> 
> The issue is only triggered for drivers which use managed irq &
> multiple hw queues.

Is the problem that the managed interrupt sets the effective irq
affinity to an offline CPU? You mentioned observed timeouts; are you
seeing the "completion polled" nvme message?