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

[Jiri Olsa <jolsa@redhat.com>]

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);

jirka