[PATCH] nvme: allow timed-out ios to retry

[keith.busch@intel.com (Keith Busch)]

On Thu, Sep 07, 2017@01:18:04PM -0700, James Smart wrote:
> Currently the nvme_req_needs_retry() applies several checks to see if
> a retry is allowed. On of those is whether the current time has exceeded
> the start time of the io plus the timeout length. This check, if an io
> times out, means there is never a retry allowed for the io. Which means
> applications see the io failure.
> 
> Remove this check and allow the io to timeout, like it does on other
> protocols, and retries to be made.
> 
> On the FC transport, a frame can be lost for an individual io, and there
> may be no other errors that escalate for the connection/association.
> The io will timeout, which causes the transport to escalate into creating
> a new association, but the io that timed out, due to this retry logic, has
> already failed back to the application and things are hosed.

I'm a bit conflicted on this. While it'd be nice to give commands a chance
to succeed after a timeout handling's controller reset, some uses would
rather a command fail fast than succeed slow, and this change could keep
a request outstanding for a very long time.

What if we have a second timeout value: one for in-flight timeout before
abort/controller resset, and another for total request lifetime?

> Signed-off-by: James Smart <james.smart at broadcom.com>
> ---
>  drivers/nvme/host/core.c | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
> index acc816b67582..90d09067a82a 100644
> --- a/drivers/nvme/host/core.c
> +++ b/drivers/nvme/host/core.c
> @@ -134,8 +134,6 @@ static inline bool nvme_req_needs_retry(struct request *req)
>  		return false;
>  	if (nvme_req(req)->status & NVME_SC_DNR)
>  		return false;
> -	if (jiffies - req->start_time >= req->timeout)
> -		return false;
>  	if (nvme_req(req)->retries >= nvme_max_retries)
>  		return false;
>  	return true;
> --