[PATCH v2 2/4] nvme-pci: limit maximum queue depth to 4095

[Hannes Reinecke]

On 5/19/21 7:43 PM, Sagi Grimberg wrote:
> We are going to use the upper 4-bits of the command_id for a generation
> counter, so enforce the new queue depth upper limit. As we enforce
> both min and max queue depth, use param_set_uint_minmax istead of
> open coding it.
> 
> Signed-off-by: Sagi Grimberg <sagi at grimberg.me>
> ---
>  drivers/nvme/host/pci.c | 15 ++++++---------
>  1 file changed, 6 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
> index a29b170701fc..ac26d242b630 100644
> --- a/drivers/nvme/host/pci.c
> +++ b/drivers/nvme/host/pci.c
> @@ -60,6 +60,8 @@ MODULE_PARM_DESC(sgl_threshold,
>  		"Use SGLs when average request segment size is larger or equal to "
>  		"this size. Use 0 to disable SGLs.");
>  
> +#define NVME_PCI_MIN_QUEUE_SIZE 2
> +#define NVME_PCI_MAX_QUEUE_SIZE 4095
>  static int io_queue_depth_set(const char *val, const struct kernel_param *kp);
>  static const struct kernel_param_ops io_queue_depth_ops = {
>  	.set = io_queue_depth_set,
> @@ -68,7 +70,7 @@ static const struct kernel_param_ops io_queue_depth_ops = {
>  
>  static unsigned int io_queue_depth = 1024;
>  module_param_cb(io_queue_depth, &io_queue_depth_ops, &io_queue_depth, 0644);
> -MODULE_PARM_DESC(io_queue_depth, "set io queue depth, should >= 2");
> +MODULE_PARM_DESC(io_queue_depth, "set io queue depth, should >= 2 and < 4096");
>  
Why do we limit it to 4095 (ie one less than 4096), but have the default
at 1024?
Shouldn't the default be one less, too?

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		        Kernel Storage Architect
hare at suse.de			               +49 911 74053 688
SUSE Software Solutions Germany GmbH, 90409 Nürnberg
GF: F. Imendörffer, HRB 36809 (AG Nürnberg)