linux-kernel - Re: [RFC PATCH v2 1/7] tracing: Add __bitmask() macro to trace events to cpumasks and other bitmasks

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Message-ID: <20140521082641.GA3025@e102654-lin.cambridge.arm.com>
Date:	Wed, 21 May 2014 09:26:41 +0100
From:	Javi Merino <javi.merino@....com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Punit Agrawal <Punit.Agrawal@....com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [RFC PATCH v2 1/7] tracing: Add __bitmask() macro to trace
 events to cpumasks and other bitmasks

Hi Steve,

On Wed, May 21, 2014 at 03:07:23AM +0100, Steven Rostedt wrote:
> Hmm, I didn't think about cross tree dependencies. I already pushed this
> patch to my for-next branch which is already in linux-next, and I do not
> rebase this branch unless there's a really good need to.
> 
> I guess I needed to make a separate branch that you could have pulled
> separately. I'm not sure how we want to proceed, unless you wait till
> Linus pulls my branch before you add this to your tree.
> 
> Maybe it would be OK to cherry pick it? I'm not sure Linus would want
> that.
> 
> Maybe I can make a separate branch that only has this patch and merge it
> into my tree, where git will handle the duplicate. But then we have a
> strange history.
> 
> How urgent is your change? Can it wait till my stuff makes it into
> Linus's tree in the 3.16 merge window?

Sorry for the confusion.  I was expecting you to merge this patch via
your tree.  I said that in the cover letter for the series, but I
should've repeated it in this patch.  I included it in the series for
completeness and I'll remove it once it reaches mainline.

Cheers,
Javi

> On Tue, 2014-05-20 at 15:10 +0100, Javi Merino wrote:
> > From: "Steven Rostedt (Red Hat)" <rostedt@...dmis.org>
> > 
> > Being able to show a cpumask of events can be useful as some events
> > may affect only some CPUs. There is no standard way to record the
> > cpumask and converting it to a string is rather expensive during
> > the trace as traces happen in hotpaths. It would be better to record
> > the raw event mask and be able to parse it at print time.
> > 
> > The following macros were added for use with the TRACE_EVENT() macro:
> > 
> >   __bitmask()
> >   __assign_bitmask()
> >   __get_bitmask()
> > 
> > To test this, I added this to the sched_migrate_task event, which
> > looked like this:
> > 
> > TRACE_EVENT(sched_migrate_task,
> > 
> > 	TP_PROTO(struct task_struct *p, int dest_cpu, const struct cpumask *cpus),
> > 
> > 	TP_ARGS(p, dest_cpu, cpus),
> > 
> > 	TP_STRUCT__entry(
> > 		__array(	char,	comm,	TASK_COMM_LEN	)
> > 		__field(	pid_t,	pid			)
> > 		__field(	int,	prio			)
> > 		__field(	int,	orig_cpu		)
> > 		__field(	int,	dest_cpu		)
> > 		__bitmask(	cpumask, num_possible_cpus()	)
> > 	),
> > 
> > 	TP_fast_assign(
> > 		memcpy(__entry->comm, p->comm, TASK_COMM_LEN);
> > 		__entry->pid		= p->pid;
> > 		__entry->prio		= p->prio;
> > 		__entry->orig_cpu	= task_cpu(p);
> > 		__entry->dest_cpu	= dest_cpu;
> > 		__assign_bitmask(cpumask, cpumask_bits(cpus), num_possible_cpus());
> > 	),
> > 
> > 	TP_printk("comm=%s pid=%d prio=%d orig_cpu=%d dest_cpu=%d cpumask=%s",
> > 		  __entry->comm, __entry->pid, __entry->prio,
> > 		  __entry->orig_cpu, __entry->dest_cpu,
> > 		  __get_bitmask(cpumask))
> > );
> > 
> > With the output of:
> > 
> >         ksmtuned-3613  [003] d..2   485.220508: sched_migrate_task: comm=ksmtuned pid=3615 prio=120 orig_cpu=3 dest_cpu=2 cpumask=00000000,0000000f
> >      migration/1-13    [001] d..5   485.221202: sched_migrate_task: comm=ksmtuned pid=3614 prio=120 orig_cpu=1 dest_cpu=0 cpumask=00000000,0000000f
> >              awk-3615  [002] d.H5   485.221747: sched_migrate_task: comm=rcu_preempt pid=7 prio=120 orig_cpu=0 dest_cpu=1 cpumask=00000000,000000ff
> >      migration/2-18    [002] d..5   485.222062: sched_migrate_task: comm=ksmtuned pid=3615 prio=120 orig_cpu=2 dest_cpu=3 cpumask=00000000,0000000f
> > 
> > Link: http://lkml.kernel.org/r/1399377998-14870-6-git-send-email-javi.merino@arm.com
> > Link: http://lkml.kernel.org/r/20140506132238.22e136d1@gandalf.local.home
> > 
> > Suggested-by: Javi Merino <javi.merino@....com>
> > Tested-by: Javi Merino <javi.merino@....com>
> > Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
> 
> 
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