On Wed, 19 Dec 2018 08:36:43 +0100
Jesper Dangaard Brouer <bro...@redhat.com> wrote:
> > +TRACE_EVENT(net_dev_notifier_entry,
> > +
> > + TP_PROTO(const struct netdev_notifier_info *info, unsigned long val),
> > +
> > + TP_ARGS(info, val),
> > +
> > + TP_STRUCT__entry(
> > + __string( name, info->dev->name )
> > + __field( enum netdev_cmd, event )
> > + ),
> > +
> > + TP_fast_assign(
> > + __assign_str(name, info->dev->name);
> > + __entry->event = val;
> > + ),
>
> These __string and __assign_str are costly and behind the scenes does a
> strcpy.
True. But you could also make this into a memcpy with:
__array( char, name, IFNAMSIZ)
And in TP_fast_assign:
memcpy(__entry->name, info->dev->name, IFNAMSIZ);
And for the TP_printk:
"dev=%s", __entry->name
Yes, ifindex is still faster, but this does give you the name in a way
that I think even BPF can use it. I also believe that memcopy on a
constant is faster than a strcpy.
-- Steve
