Re: [PATCH v2 1/1] SUNRPC dont update timeout value on connection reset

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Hi Olga,

On Mon, 2020-07-13 at 12:18 -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.
> 
> v2: using the suggested approach by Trond Myklebust and not use the 
> sliding timeout. 
> 
> Signed-off-by: Olga Kornievskaia <kolga@xxxxxxxxxx>
> ---
>  include/linux/sunrpc/xprt.h | 1 +
>  net/sunrpc/xprt.c           | 9 +++++++++
>  2 files changed, 10 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..92fc9fd 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;

Shouldn't this just be: req->rq_minortimeo += 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 +637,8 @@ 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))
> +		return status;
>  	if (time_before(jiffies, req->rq_majortimeo)) {
>  		if (to->to_exponential)
>  			req->rq_timeout <<= 1;
> @@ -649,6 +657,7 @@ int xprt_adjust_timeout(struct rpc_rqst *req)
>  		spin_unlock(&xprt->transport_lock);
>  		status = -ETIMEDOUT;
>  	}
> +	xprt_reset_minortimeo(req);
>  
>  	if (req->rq_timeout == 0) {
>  		printk(KERN_WARNING "xprt_adjust_timeout: rq_timeout =
> 0!\n");

Otherwise it looks good to me.

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






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