On Wed, Jul 12, 2023 at 03:00:17PM +0200, Christoph Hellwig wrote:
> On Wed, Jul 12, 2023 at 08:54:48PM +0800, Ming Lei wrote:
> > +/* Max nr_hw_queues for each hw queue type */
> > +unsigned int blk_mq_max_nr_hw_queues(void)
> > +{
> > + if (is_kdump_kernel())
> > + return 1;
> > + return nr_cpu_ids;
>
> Again, these is_kdump_kernel hacks don't make any sense. The amount
> of maximum available CPU needs to come through a proper API, and we
> need to use it, not add hacks like this.
>
> The only thing that makes sense here is to find the last CPU
> in cpu_possible_mask, and for kdump kernels to ensure that number
> is 1 or whatever low value they want.
It doesn't matter how many cpus are available, given at least one
cpu is online.
The problem is that blk_mq_alloc_tag_set() forces to set nr_hw_queues
as 1 for kdump kernel, that is why blk_mq_max_nr_hw_queues() has to
return 1 for kdump kernel.
We have to tell driver that blk-mq only supports 1 queue for kdump
kernel.
Or:
Thomas, can we disable managed irq for kdump kernel and switch to
non-managed irq? Then we can avoid driver's change. I'd suggest
this way if it is possible.
Thanks,
Ming
