Re: [PATCH RT] tracing: make preempt_lazy and migrate_disable counter smaller

Sebastian Andrzej Siewior
2020-02-21T20:20:57Z

On 2020-02-21 14:51:48 [-0500], Steven Rostedt wrote:
> On Fri, 21 Feb 2020 18:44:19 +0100
> Sebastian Andrzej Siewior <bigeasy@linutronix.de> wrote:
>
> > diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
> > index f3b1ef07e4a5f..c8b3f06cb5ed7 100644
> > --- a/include/linux/trace_events.h
> > +++ b/include/linux/trace_events.h
> > @@ -62,9 +62,9 @@ struct trace_entry {
> > unsigned char flags;
> > unsigned char preempt_count;
> > int pid;
> > - unsigned short migrate_disable;
> > - unsigned short padding;
> > + unsigned char migrate_disable;
> > unsigned char preempt_lazy_count;
> > + unsigned short padding;
> > };
>
> Do we really need the padding here?

Not really. The two bytes are consumed since there is __packed so that
padding makes it just more obvious. However that padding wasn't used in
the past. I can remove it if you want.
The struct can't be __packed to save additional two bytes, correct?

> -- Steve

Sebastian