Re: [PATCH 1/1] SUNRPC dont update timeout value on connection reset

[Trond Myklebust <trondmy@hammerspace.com>]

Hi Olga

On Wed, 2020-07-08 at 17:05 -0400, Olga Kornievskaia wrote:
> Current behaviour: every time a v3 operation is re-sent to the server
> we update (double) the timeout. There is no distinction between
> whether
> or not the previous timer had expired before the re-sent happened.
> 
> Here's the scenario:
> 1. Client sends a v3 operation
> 2. Server RST-s the connection (prior to the timeout) (eg.,
> connection
> is immediately reset)
> 3. Client re-sends a v3 operation but the timeout is now 120sec.
> 
> As a result, an application sees 2mins pause before a retry in case
> server again does not reply.
> 
> Instead, this patch proposes to keep track off when the minor timeout
> should happen and if it didn't, then don't update the new timeout.
> 
> Signed-off-by: Olga Kornievskaia <kolga@netapp.com>
> ---
>  include/linux/sunrpc/xprt.h |  1 +
>  net/sunrpc/xprt.c           | 11 +++++++++++
>  2 files changed, 12 insertions(+)
> 
> diff --git a/include/linux/sunrpc/xprt.h
> b/include/linux/sunrpc/xprt.h
> index e64bd82..a603d48 100644
> --- a/include/linux/sunrpc/xprt.h
> +++ b/include/linux/sunrpc/xprt.h
> @@ -101,6 +101,7 @@ struct rpc_rqst {
>  							 * used in the
> softirq.
>  							 */
>  	unsigned long		rq_majortimeo;	/* major timeout
> alarm */
> +	unsigned long		rq_minortimeo;	/* minor timeout
> alarm */
>  	unsigned long		rq_timeout;	/* Current timeout
> value */
>  	ktime_t			rq_rtt;		/* round-trip time */
>  	unsigned int		rq_retries;	/* # of retries */
> diff --git a/net/sunrpc/xprt.c b/net/sunrpc/xprt.c
> index d5cc5db..c0ce232 100644
> --- a/net/sunrpc/xprt.c
> +++ b/net/sunrpc/xprt.c
> @@ -607,6 +607,11 @@ static void xprt_reset_majortimeo(struct
> rpc_rqst *req)
>  	req->rq_majortimeo += xprt_calc_majortimeo(req);
>  }
>  
> +static void xprt_reset_minortimeo(struct rpc_rqst *req)
> +{
> +	req->rq_minortimeo = jiffies + req->rq_timeout;
> +}
> +
>  static void xprt_init_majortimeo(struct rpc_task *task, struct
> rpc_rqst *req)
>  {
>  	unsigned long time_init;
> @@ -618,6 +623,7 @@ static void xprt_init_majortimeo(struct rpc_task
> *task, struct rpc_rqst *req)
>  		time_init = xprt_abs_ktime_to_jiffies(task->tk_start);
>  	req->rq_timeout = task->tk_client->cl_timeout->to_initval;
>  	req->rq_majortimeo = time_init + xprt_calc_majortimeo(req);
> +	req->rq_minortimeo = time_init + req->rq_timeout;
>  }
>  
>  /**
> @@ -631,6 +637,10 @@ int xprt_adjust_timeout(struct rpc_rqst *req)
>  	const struct rpc_timeout *to = req->rq_task->tk_client-
> >cl_timeout;
>  	int status = 0;
>  
> +	if (time_before(jiffies, req->rq_minortimeo)) {
> +		xprt_reset_minortimeo(req);
> +		return status;

Shouldn't this case be just returning without updating the timeout?
After all, this is the case where nothing has expired yet.

> +	}
>  	if (time_before(jiffies, req->rq_majortimeo)) {
>  		if (to->to_exponential)
>  			req->rq_timeout <<= 1;
> @@ -638,6 +648,7 @@ int xprt_adjust_timeout(struct rpc_rqst *req)
>  			req->rq_timeout += to->to_increment;
>  		if (to->to_maxval && req->rq_timeout >= to->to_maxval)
>  			req->rq_timeout = to->to_maxval;
> +		xprt_reset_minortimeo(req);

...and then perhaps this can just be moved out of the time_before()
condition, since it looks to me as if we also want to reset req-
>rq_minortimeo when a major timeout occurs.

>  		req->rq_retries++;
>  	} else {
>  		req->rq_timeout = to->to_initval;


-- 
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@hammerspace.com