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Subject: Re: [PATCH] nvme: determine the number of IO queues
To:     Aaron Ma <aaron.ma@canonical.com>, linux-kernel@vger.kernel.org,
        linux-nvme@lists.infradead.org, keith.busch@intel.com, axboe@fb.com
References: <1555510379-20199-1-git-send-email-aaron.ma@canonical.com>
From:   "Edmund Nadolski (Microsoft)" <edmund.f.nadolski@gmail.com>
Message-ID: <08ac5733-596b-598d-c821-f1aa2dc32650@gmail.com>
Date:   Wed, 17 Apr 2019 14:30:18 -0700
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On 4/17/19 7:12 AM, Aaron Ma wrote:
> Some controllers support limited IO queues, when over set
> the number, it will return invalid field error.
> Then NVME will be removed by driver.
> 
> Find the max number of IO queues that controller supports.
> When it still got invalid result, set 1 IO queue at least to
> bring NVME online.
> 
> Signed-off-by: Aaron Ma <aaron.ma@canonical.com>
> ---
>   drivers/nvme/host/core.c | 29 ++++++++++++++++++-----------
>   1 file changed, 18 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
> index 2c43e12b70af..fb7f05c310c8 100644
> --- a/drivers/nvme/host/core.c
> +++ b/drivers/nvme/host/core.c
> @@ -1134,14 +1134,24 @@ static int nvme_set_features(struct nvme_ctrl *dev, unsigned fid, unsigned dword
>   
>   int nvme_set_queue_count(struct nvme_ctrl *ctrl, int *count)
>   {
> -	u32 q_count = (*count - 1) | ((*count - 1) << 16);
> +	u32 q_count;
>   	u32 result;
> -	int status, nr_io_queues;
> -
> -	status = nvme_set_features(ctrl, NVME_FEAT_NUM_QUEUES, q_count, NULL, 0,
> -			&result);
> -	if (status < 0)
> -		return status;
> +	int status = -1;
> +	int nr_io_queues;
> +	int try_count;
> +
> +	for (try_count = *count; try_count > 0; try_count--) {
> +		q_count = (try_count - 1) | ((try_count - 1) << 16);

A macro here might help readability.

> +		status = nvme_set_features(ctrl, NVME_FEAT_NUM_QUEUES,
> +				q_count, NULL, 0, &result);
> +		if (status < 0)
> +			return status;
> +		else if (status == 0) {

else following return is not needed.


> +			nr_io_queues = min(result & 0xffff, result >> 16) + 1;

Likewise, a macro as above.


Ed

> +			*count = min(try_count, nr_io_queues);
> +			break;
> +		}
> +	}
>   
>   	/*
>   	 * Degraded controllers might return an error when setting the queue
> @@ -1150,10 +1160,7 @@ int nvme_set_queue_count(struct nvme_ctrl *ctrl, int *count)
>   	 */
>   	if (status > 0) {
>   		dev_err(ctrl->device, "Could not set queue count (%d)\n", status);
> -		*count = 0;
> -	} else {
> -		nr_io_queues = min(result & 0xffff, result >> 16) + 1;
> -		*count = min(*count, nr_io_queues);
> +		*count = 1;
>   	}
>   
>   	return 0;
>