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    SubjectRe: [PATCH 2/2] Markers Implementation for Preempt RCU Boost Tracing
    On Sat, Jan 05, 2008 at 07:46:32AM -0500, Mathieu Desnoyers wrote:
    > * Gautham R Shenoy (ego@in.ibm.com) wrote:
    > > On Thu, Jan 03, 2008 at 11:30:55AM -0500, Mathieu Desnoyers wrote:
    > > > * K. Prasad (prasad@linux.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@linux.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

    Hi Mathieu,
    Thanks for your suggestions.

    Even in functions such as rcu_check_callbacks_rt, rcu_advance_callbacks_rt and
    __rcu_advance_callbacks, where a call to RCU_TRACE_RDP() is made, the
    'cpu' variable is populated at an early stage with the
    return value of smp_processor_id().

    __rcu_advance_callbacks() <-- rcu_check_callbacks_rt() <--
    rcu_check_callbacks() <-- update_process_times().

    update_process_times() [if understood correctly, is called at timer
    interrupt level] populates the 'cpu' with smp_processor_id().

    There doesn't seem to be a need to pass down the 'cpu' parameter for
    the above RCU functions including respective trace_mark() calls.

    I am re-sending the patches with your suggested changes in subsequent
    mails.

    Thanks,
    K.Prasad

    >
    > >
    > > 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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