linux-kernel - Re: [PATCH] trace: Add migrate-disabled counter to tracing output.

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Date:   Fri, 6 Aug 2021 20:10:44 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] trace: Add migrate-disabled counter to tracing output.

On 2021-08-06 13:51:24 [-0400], Steven Rostedt wrote:
> > diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
> > index ad413b382a3ca..7c4280b4c6be7 100644
> > --- a/include/linux/trace_events.h
> > +++ b/include/linux/trace_events.h
> > @@ -69,6 +69,7 @@ struct trace_entry {
> >  	unsigned char		flags;
> >  	unsigned char		preempt_count;
> >  	int			pid;
> > +	unsigned char		migrate_disable;
> 
> The only issue I have with this patch is this part. It extends the
> header of all events beyond 8 bytes, and actually adds another 4 or 8
> bytes despite being just a char in size. That's because this is a
> header of a structure, which depending on the first field of an event,
> padding may be added to have 4 or 8 byte alignment.
> 
> I'll be fine with merging this counter with either flags or
> preempt_count (neither needs all 8 bits). I can figure out how to
> update libtraceevent to handle this case.

I was kind of expecting that. Let me try 4 bits for the preempt counter
and 4 bits for the migrate counter.

> -- Steve
> 

Sebastian