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Date:   Wed, 1 May 2019 20:55:03 +0000
From:   Saeed Mahameed <saeedm@...lanox.com>
To:     Eran Ben Elisha <eranbe@...lanox.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "xiyou.wangcong@...il.com" <xiyou.wangcong@...il.com>
CC:     Jiri Pirko <jiri@...lanox.com>
Subject: Re: [Patch net-next] net: add a generic tracepoint for TX queue
 timeout

On Wed, 2019-05-01 at 13:11 +0000, Eran Ben Elisha wrote:
> 
> On 4/30/2019 9:50 PM, Cong Wang wrote:
> > Although devlink health report does a nice job on reporting TX
> > timeout and other NIC errors, unfortunately it requires drivers
> > to support it but currently only mlx5 has implemented it.
> 
> The devlink health was never intended to be the generic mechanism
> for 
> monitoring all driver's TX timeouts notifications. mlx5e driver chose
> to 
> handle TX timeout notification by reporting it to the newly devlink 
> health mechanism.
> 
> > Before other drivers could catch up, it is useful to have a
> > generic tracepoint to monitor this kind of TX timeout. We have
> > been suffering TX timeout with different drivers, we plan to
> > start to monitor it with rasdaemon which just needs a new
> > tracepoint.
> 
> Great idea to suggest a generic trace message that can be monitored
> over 
> all drivers.
> 

+1

I would also add skb->xmit_more indication to net_dev_start_xmit
tracepoint (in a separate patch), many tx timeout debugs revealed a
buggy usage of skb->xmit_more, where xmit_more was set but no further
SKBs arrived.

> > Sample output:
> > 
> >    ksoftirqd/1-16    [001] ..s2   144.043173: net_dev_xmit_timeout:
> > dev=ens3 driver=e1000 queue=0
> > 
> > Cc: Eran Ben Elisha <eranbe@...lanox.com>
> > Cc: Jiri Pirko <jiri@...lanox.com>
> > Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>
> > ---
> >   include/trace/events/net.h | 23 +++++++++++++++++++++++
> >   net/sched/sch_generic.c    |  2 ++
> >   2 files changed, 25 insertions(+)
> > 
> > diff --git a/include/trace/events/net.h
> > b/include/trace/events/net.h
> > index 1efd7d9b25fe..002d6f04b9e5 100644
> > --- a/include/trace/events/net.h
> > +++ b/include/trace/events/net.h
> > @@ -303,6 +303,29 @@ DEFINE_EVENT(net_dev_rx_exit_template,
> > netif_receive_skb_list_exit,
> >   	TP_ARGS(ret)
> >   );
> >   
> 
> I would have put this next to net_dev_xmit trace event declaration.
> 
> > +TRACE_EVENT(net_dev_xmit_timeout,
> > +
> > +	TP_PROTO(struct net_device *dev,
> > +		 int queue_index),
> > +
> > +	TP_ARGS(dev, queue_index),
> > +
> > +	TP_STRUCT__entry(
> > +		__string(	name,		dev->name	)
> > +		__string(	driver,		netdev_drivername(dev))
> > +		__field(	int,		queue_index	)
> > +	),
> > +
> > +	TP_fast_assign(
> > +		__assign_str(name, dev->name);
> > +		__assign_str(driver, netdev_drivername(dev));
> > +		__entry->queue_index = queue_index;
> > +	),
> > +
> > +	TP_printk("dev=%s driver=%s queue=%d",
> > +		__get_str(name), __get_str(driver), __entry-
> > >queue_index)
> > +);
> > +
> >   #endif /* _TRACE_NET_H */
> >   
> >   /* This part must be outside protection */
> > diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
> > index 848aab3693bd..cce1e9ee85af 100644
> > --- a/net/sched/sch_generic.c
> > +++ b/net/sched/sch_generic.c
> > @@ -32,6 +32,7 @@
> >   #include <net/pkt_sched.h>
> >   #include <net/dst.h>
> >   #include <trace/events/qdisc.h>
> > +#include <trace/events/net.h>
> >   #include <net/xfrm.h>
> >   
> >   /* Qdisc to use by default */
> > @@ -441,6 +442,7 @@ static void dev_watchdog(struct timer_list *t)
> >   			}
> >   
> >   			if (some_queue_timedout) {
> > +				trace_net_dev_xmit_timeout(dev, i);
> >   				WARN_ONCE(1, KERN_INFO "NETDEV
> > WATCHDOG: %s (%s): transmit queue %u timed out\n",
> >   				       dev->name,
> > netdev_drivername(dev), i);
> >   				dev->netdev_ops->ndo_tx_timeout(dev);
> > 

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