[PATCH 3/3] nvme: add parameter command_retry to enable retry

[Chao Leng]

On 2021/1/8 22:46, Minwoo Im wrote:
> nvme_init_request() has set REQ_FAILFAST_DRIVER to make requests
> non-retryable.  This command flag value is checked in
> nvme_decide_disposition() to decide whether to RETRY or other
> operations.  In that point, blk_noretry_request() macro will be used to
> check if command flags have one of REQ_FAILFAST_*.  If so, it just
> decides to complete the request without retrying.
> 
> This patch added a module parameter named command_retry to turn on the
> command retry feature in this driver.  If turning it on,
> REQ3_FAILFAST_DRIVER will not be set to requests so that retry can be
> reached out to nvme_retry_req() based on the module parameter.
> 
> Signed-off-by: Minwoo Im <minwoo.im.dev at gmail.com>
> ---
>   drivers/nvme/host/core.c | 7 ++++++-
>   1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
> index 6e428fdc25a8..e1836ca9956f 100644
> --- a/drivers/nvme/host/core.c
> +++ b/drivers/nvme/host/core.c
> @@ -44,6 +44,10 @@ static unsigned char shutdown_timeout = 5;
>   module_param(shutdown_timeout, byte, 0644);
>   MODULE_PARM_DESC(shutdown_timeout, "timeout in seconds for controller shutdown");
>   
> +static bool command_retry;
> +module_param(command_retry, bool, 0644);
> +MODULE_PARM_DESC(command_retry, "retry commands up to nvme_max_retries");
> +
>   static u8 nvme_max_retries = 5;
>   module_param_named(max_retries, nvme_max_retries, byte, 0644);
>   MODULE_PARM_DESC(max_retries, "max number of retries a command may have");
> @@ -560,7 +564,8 @@ static inline void nvme_init_request(struct request *req,
>   	else /* no queuedata implies admin queue */
>   		req->timeout = NVME_ADMIN_TIMEOUT;
>   
> -	req->cmd_flags |= REQ_FAILFAST_DRIVER;
> +	if (!command_retry)
> +		req->cmd_flags |= REQ_FAILFAST_DRIVER;
In abnormal scenarios, such as request time out, connection process may takes long time or the admin command waits for long time.
Retry only for non-host errors may be a better choice. Maybe we can make some optimizations in nvme_decide_disposition.
>   	nvme_clear_nvme_request(req);
>   	nvme_req(req)->cmd = cmd;
>   }
>