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

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

On 2020-02-21 21:49:57 [+0100], Jiri Olsa wrote:
> On Fri, Feb 21, 2020 at 06:44:19PM +0100, Sebastian Andrzej Siewior wrote:
> > The migrate_disable counter should not exceed 255 so it is enough to
> > store it in an 8bit field.
> > With this change we can move the `preempt_lazy_count' member into the
> > gap so the whole struct shrinks by 4 bytes to 12 bytes in total.
> > 
> > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> > ---
> >  include/linux/trace_events.h | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > 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;
> 
> also we still need to put preempt_lazy_count as common field:
> 
> 	__common_field(unsigned char,  preempt_lazy_count);

so I need to update the struct as I did (and drop the padding field like
Steven suggested) and then do the "same" change to
"trace_define_common_fields" ?

> 
> jirka

Sebastian