Re: [PATCH v2 02/12] sunrpc: add info about xprt queue times to svc_xprt_dequeue tracepoint

[Chuck Lever <chuck.lever@oracle.com>]

On 4/9/25 10:32 AM, Jeff Layton wrote:
> Currently, this tracepoint displays "wakeup-us", which is the time that
> the woken thread spent sleeping, before dequeueing the next xprt. Add a
> new statistic that shows how long the xprt sat on the queue before being
> serviced.

I don't understand the difference between "waiting on queue" and
"sleeping". When are those two latency measurements not the same?


> Signed-off-by: Jeff Layton <jlayton@kernel.org>
> ---
>  include/linux/sunrpc/svc_xprt.h |  1 +
>  include/trace/events/sunrpc.h   | 13 +++++++------
>  net/sunrpc/svc_xprt.c           |  1 +
>  3 files changed, 9 insertions(+), 6 deletions(-)
> 
> diff --git a/include/linux/sunrpc/svc_xprt.h b/include/linux/sunrpc/svc_xprt.h
> index 72be609525796792274d5b8cb5ff37f73723fc23..369a89aea18618748607ee943247c327bf62c8d5 100644
> --- a/include/linux/sunrpc/svc_xprt.h
> +++ b/include/linux/sunrpc/svc_xprt.h
> @@ -53,6 +53,7 @@ struct svc_xprt {
>  	struct svc_xprt_class	*xpt_class;
>  	const struct svc_xprt_ops *xpt_ops;
>  	struct kref		xpt_ref;
> +	ktime_t			xpt_qtime;
>  	struct list_head	xpt_list;
>  	struct lwq_node		xpt_ready;
>  	unsigned long		xpt_flags;
> diff --git a/include/trace/events/sunrpc.h b/include/trace/events/sunrpc.h
> index 5d331383047b79b9f6dcd699c87287453c1a5f49..b5a0f0bc1a3b7cfd90ce0181a8a419db810988bb 100644
> --- a/include/trace/events/sunrpc.h
> +++ b/include/trace/events/sunrpc.h
> @@ -2040,19 +2040,20 @@ TRACE_EVENT(svc_xprt_dequeue,
>  
>  	TP_STRUCT__entry(
>  		SVC_XPRT_ENDPOINT_FIELDS(rqst->rq_xprt)
> -
>  		__field(unsigned long, wakeup)
> +		__field(unsigned long, qtime)
>  	),
>  
>  	TP_fast_assign(
> -		SVC_XPRT_ENDPOINT_ASSIGNMENTS(rqst->rq_xprt);
> +		ktime_t ktime = ktime_get();
>  
> -		__entry->wakeup = ktime_to_us(ktime_sub(ktime_get(),
> -							rqst->rq_qtime));
> +		SVC_XPRT_ENDPOINT_ASSIGNMENTS(rqst->rq_xprt);
> +		__entry->wakeup = ktime_to_us(ktime_sub(ktime, rqst->rq_qtime));
> +		__entry->qtime = ktime_to_us(ktime_sub(ktime, rqst->rq_xprt->xpt_qtime));
>  	),
>  
> -	TP_printk(SVC_XPRT_ENDPOINT_FORMAT " wakeup-us=%lu",
> -		SVC_XPRT_ENDPOINT_VARARGS, __entry->wakeup)
> +	TP_printk(SVC_XPRT_ENDPOINT_FORMAT " wakeup-us=%lu qtime=%lu",
> +		SVC_XPRT_ENDPOINT_VARARGS, __entry->wakeup, __entry->qtime)
>  );
>  
>  DECLARE_EVENT_CLASS(svc_xprt_event,
> diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
> index ae25405d8bd22672a361d1fd3adfdcebb403f90f..32018557797b1f683d8b7259f5fccd029aebcd71 100644
> --- a/net/sunrpc/svc_xprt.c
> +++ b/net/sunrpc/svc_xprt.c
> @@ -488,6 +488,7 @@ void svc_xprt_enqueue(struct svc_xprt *xprt)
>  	pool = svc_pool_for_cpu(xprt->xpt_server);
>  
>  	percpu_counter_inc(&pool->sp_sockets_queued);
> +	xprt->xpt_qtime = ktime_get();
>  	lwq_enqueue(&xprt->xpt_ready, &pool->sp_xprts);
>  
>  	svc_pool_wake_idle_thread(pool);
> 


-- 
Chuck Lever