linux-kernel - Re: [PATCH 2/2] Markers Implementation for Preempt RCU Boost Tracing

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Message-ID: <20080105124632.GA16576@Krystal>
Date:	Sat, 5 Jan 2008 07:46:32 -0500
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Gautham R Shenoy <ego@...ibm.com>
Cc:	"K. Prasad" <prasad@...ux.vnet.ibm.com>, mingo@...e.hu,
	linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org,
	dipankar@...ibm.com, paulmck@...ux.vnet.ibm.com
Subject: Re: [PATCH 2/2] Markers Implementation for Preempt RCU Boost
	Tracing

* Gautham R Shenoy (ego@...ibm.com) wrote:
> On Thu, Jan 03, 2008 at 11:30:55AM -0500, Mathieu Desnoyers wrote:
> > * K. Prasad (prasad@...ux.vnet.ibm.com) wrote:
> > > This patch converts the tracing mechanism of Preempt RCU boosting into
> > > markers. The handler functions for these markers are included inside
> > > rcupreempt_trace.c and will be included only when PREEMPT_RCU_BOOST is
> > > chosen.
> > >  
> > > Signed-off-by: K.Prasad <prasad@...ux.vnet.ibm.com>
> > > ---
> > >  include/linux/rcupreempt_trace.h |   46 ++++++++
> > >  kernel/rcupreempt-boost.c        |  211 ++++-----------------------------------
> > >  kernel/rcupreempt_trace.c        |  183 +++++++++++++++++++++++++++++++++
> > >  3 files changed, 251 insertions(+), 189 deletions(-)
> > >  
> > > Index: linux-2.6.24-rc2-rt1.MARKER_PATCHES_NEW/include/linux/rcupreempt_trace.h
> > > ===================================================================
> > > --- linux-2.6.24-rc2-rt1.MARKER_PATCHES_NEW.orig/include/linux/rcupreempt_trace.h
> > > +++ linux-2.6.24-rc2-rt1.MARKER_PATCHES_NEW/include/linux/rcupreempt_trace.h
> > > @@ -102,5 +102,51 @@ extern int rcupreempt_flip_flag(int cpu)
> > >  extern int rcupreempt_mb_flag(int cpu);
> > >  extern char *rcupreempt_try_flip_state_name(void);
> > >  
> > > +#ifdef CONFIG_PREEMPT_RCU_BOOST
> > > +struct preempt_rcu_boost_trace {
> > > +	unsigned long rbs_stat_task_boost_called;
> > > +	unsigned long rbs_stat_task_boosted;
> > > +	unsigned long rbs_stat_boost_called;
> > > +	unsigned long rbs_stat_try_boost;
> > > +	unsigned long rbs_stat_boosted;
> > > +	unsigned long rbs_stat_unboost_called;
> > > +	unsigned long rbs_stat_unboosted;
> > > +	unsigned long rbs_stat_try_boost_readers;
> > > +	unsigned long rbs_stat_boost_readers;
> > > +	unsigned long rbs_stat_try_unboost_readers;
> > > +	unsigned long rbs_stat_unboost_readers;
> > > +	unsigned long rbs_stat_over_taken;
> > > +};
> > > +
> > > +#define DEFINE_PREEMPT_RCU_BOOST_MARKER_HANDLER(preempt_rcu_boost_var) \
> > > +void preempt_rcu_boost_var##_callback(const struct marker *mdata, \
> > > +				void *private_data, const char *format, ...) \
> > > +{ \
> > > +	va_list ap; \
> > > +	int cpu; \
> > > +	struct preempt_rcu_boost_trace *boost_trace; \
> > > +	va_start(ap, format); \
> > > +	cpu = va_arg(ap, typeof(unsigned int)); \
> > 
> > (sorry for late response, I just came back from vacation)
> > 
> > Instead of passing the cpu id as a marker parameter, why don't you
> > simply use smp_processor_id() right here ?
> > 
> 
> Agreed. 
> 
> Also in patch 1, in cases where we're using markers in place of RCU_TRACE_ME(), 
> we need not pass the parameter and simply use smp_processor_id().
> 
> It's only the RCU_TRACE_RDP() that requires cpuid to be passed.
> 


And it would help if you declare the format string with something like :

"cpuid %u" instead of "%u"

This way, if a generic tracer like LTTng dumps the traces and later a
plugin in an analysis tool like LTTV have to hook on a specific field of
your event, it can access it by specifying the marker name and field
name. And even if fields are added to this event, it won't break
compatibility as long as this field is there and have the same name.

Mathieu

> 
> Thanks and Regards
> gautham.
> 
> 
> > -- 
> > Mathieu Desnoyers
> > Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
> > OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
> 
> -- 
> Gautham R Shenoy
> Linux Technology Center
> IBM India.
> "Freedom comes with a price tag of responsibility, which is still a bargain,
> because Freedom is priceless!"

-- 
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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