linux-kernel - Re: [PATCH 1/1] trace: use the more accurate parameter.

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Message-ID: <alpine.DEB.1.10.0902130053210.15469@gandalf.stny.rr.com>
Date:	Fri, 13 Feb 2009 00:56:31 -0500 (EST)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Ingo Molnar <mingo@...e.hu>
cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Wenji Huang <wenji.huang@...cle.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] trace: use the more accurate parameter.


On Wed, 11 Feb 2009, Ingo Molnar wrote:

> 
> * Frederic Weisbecker <fweisbec@...il.com> wrote:
> 
> > On Mon, Feb 09, 2009 at 07:30:04PM -0500, Wenji Huang wrote:
> > > Pass tsk to __update_max_tr instead of current to avoid latent hazard.
> > > 
> > > Impact: clean up
> > > 
> > > Signed-off-by: Wenji Huang <wenji.huang@...cle.com>
> > > ---
> > >  kernel/trace/trace.c |    2 +-
> > >  1 files changed, 1 insertions(+), 1 deletions(-)
> > > 
> > > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> > > index 5b1e9a9..c1592f1 100644
> > > --- a/kernel/trace/trace.c
> > > +++ b/kernel/trace/trace.c
> > > @@ -335,7 +335,7 @@ __update_max_tr(struct trace_array *tr, struct task_struct *tsk, int cpu)
> > >  	data->rt_priority = tsk->rt_priority;
> > >  
> > >  	/* record this tasks comm */
> > > -	tracing_record_cmdline(current);
> > > +	tracing_record_cmdline(tsk);
> > >  }
> > 
> > 
> > Indeed. At this stage, tsk is the next task in the middle of a context
> > switch. So I guess current is right, but this is more proper to use tsk.
> 
> Rename it to 'next' then please.

I'm sorry, I missed this comment, and only notice it because of Wenji's 
latest patches.

For the __update_max_tr used by irqsoff, this is not the case. The 
update_max_tr is just to make a snapshot of the latest max. The 
irq/preempt latency tracers do not use the sched switch to record comms, 
especially since it only cares when a new max happens. There is no concept 
of a 'next' task.

I think the proper name is 'task'.

-- Steve

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