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Date:   Fri, 21 Feb 2020 21:20:53 +0100
From:   Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To:     Steven Rostedt <rostedt@goodmis.org>
Cc:     Jiri Olsa <jolsa@redhat.com>, Jiri Olsa <jolsa@kernel.org>,
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        Thomas Gleixner <tglx@linutronix.de>,
        Juri Lelli <juri.lelli@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>
Subject: Re: [PATCH RT] tracing: make preempt_lazy and migrate_disable
 counter smaller
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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