Re: [PATCH V2 5/9] scsi: hisi: take blk_mq_max_nr_hw_queues() into account for calculating io vectors

[John Garry <john.g.garry@oracle.com>]

On 26/07/2023 10:40, 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 kernel command line,
> see `Documentation/admin-guide/kdump/kdump.rst`, so num_possible_cpus()
> still returns all CPUs because 'maxcpus=1' just bring up one single
> cpu core during booting.
> 
> blk-mq sees single queue in kdump kernel, and in driver's viewpoint
> there are still multiple queues, this inconsistency causes driver to apply
> wrong queue mapping for handling IO, and IO timeout is triggered.
> 
> Meantime, single queue makes much less resource utilization, and reduce
> risk of kernel failure.
> 
> Cc: Xiang Chen <chenxiang66@hisilicon.com>
> Signed-off-by: Ming Lei <ming.lei@redhat.com>
> ---
>   drivers/scsi/hisi_sas/hisi_sas_v3_hw.c | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/scsi/hisi_sas/hisi_sas_v3_hw.c b/drivers/scsi/hisi_sas/hisi_sas_v3_hw.c
> index 20e1607c6282..60d2301e7f9d 100644
> --- a/drivers/scsi/hisi_sas/hisi_sas_v3_hw.c
> +++ b/drivers/scsi/hisi_sas/hisi_sas_v3_hw.c
> @@ -2550,6 +2550,9 @@ static int interrupt_preinit_v3_hw(struct hisi_hba *hisi_hba)
>   
>   
>   	hisi_hba->cq_nvecs = vectors - BASE_VECTORS_V3_HW - hisi_hba->iopoll_q_cnt;
> +	if (hisi_hba->cq_nvecs > scsi_max_nr_hw_queues())
> +		hisi_hba->cq_nvecs = scsi_max_nr_hw_queues();
> +
>   	shost->nr_hw_queues = hisi_hba->cq_nvecs + hisi_hba->iopoll_q_cnt;

For other drivers you limit the max MSI vectors which we try to allocate 
according to scsi_max_nr_hw_queues(), but here you continue to alloc the 
same max vectors but then limit the driver's completion queue count. Why 
not limit the max MSI vectors also here?

Thanks,
John

>   
>   	return devm_add_action(&pdev->dev, hisi_sas_v3_free_vectors, pdev);