Re: [RFC][PATCH 1/4] perf: core, add group scheduling transactional APIs

[Frederic Weisbecker <fweisbec@gmail.com>]

On Fri, Apr 23, 2010 at 10:08:25AM +0800, Lin Ming wrote:
> On Fri, 2010-04-23 at 01:31 +0800, Frederic Weisbecker wrote:
> > On Thu, Apr 22, 2010 at 03:51:02PM +0800, Lin Ming wrote:
> > > Add group scheduling transactional APIs to struct pmu.
> > > These APIs will be implemented in arch code, based on Peter's idea as
> > > below.
> > > 
> > > > the idea behind hw_perf_group_sched_in() is to not perform
> > > > schedulability tests on each event in the group, but to add the group
> > > as
> > > > a whole and then perform one test.
> > > >
> > > > Of course, when that test fails, you'll have to roll-back the whole
> > > > group again.
> > > >
> > > > So start_txn (or a better name) would simply toggle a flag in the pmu
> > > > implementation that will make pmu::enable() not perform the
> > > > schedulablilty test.
> > > >
> > > > Then commit_txn() will perform the schedulability test (so note the
> > > > method has to have a !void return value, my mistake in the earlier
> > > > email).
> > > >
> > > > This will allow us to use the regular
> > > > kernel/perf_event.c::group_sched_in() and all the rollback code.
> > > > Currently each hw_perf_group_sched_in() implementation duplicates all
> > > > the rolllback code (with various bugs).
> > > 
> > > 
> > > Reviewed-by: Stephane Eranian <eranian@google.com>
> > > Reviewed-by: Peter Zijlstra <peterz@infradead.org>
> > > Signed-off-by: Lin Ming <ming.m.lin@intel.com>
> > > ---
> > >  include/linux/perf_event.h |    8 +++++---
> > >  kernel/perf_event.c        |   29 ++++++++++++++++-------------
> > >  2 files changed, 21 insertions(+), 16 deletions(-)
> > > 
> > > diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> > > index ace31fb..b16cfba 100644
> > > --- a/include/linux/perf_event.h
> > > +++ b/include/linux/perf_event.h
> > > @@ -532,6 +532,8 @@ struct hw_perf_event {
> > >  
> > >  struct perf_event;
> > >  
> > > +#define PERF_EVENT_TRAN_STARTED 1
> > > +
> > >  /**
> > >   * struct pmu - generic performance monitoring unit
> > >   */
> > > @@ -542,6 +544,9 @@ struct pmu {
> > >  	void (*stop)			(struct perf_event *event);
> > >  	void (*read)			(struct perf_event *event);
> > >  	void (*unthrottle)		(struct perf_event *event);
> > > +	void (*start_txn)		(const struct pmu *pmu);
> > > +	void (*stop_txn)		(const struct pmu *pmu);
> > > +	int (*commit_txn)		(const struct pmu *pmu);
> > 
> > 
> > Please add a few comments that briefly explain what these
> > *_txn callbacks are supposed to mean.
> > 
> > Unless txn is an acronym that most kernel developers are used to.
> 
> How about below changes?
> 
> Thanks for review.
> 
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index b16cfba..bba4c60 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -544,9 +544,21 @@ struct pmu {
>  	void (*stop)			(struct perf_event *event);
>  	void (*read)			(struct perf_event *event);
>  	void (*unthrottle)		(struct perf_event *event);
> -	void (*start_txn)		(const struct pmu *pmu);
> -	void (*stop_txn)		(const struct pmu *pmu);
> -	int (*commit_txn)		(const struct pmu *pmu);
> +
> +	/*
> +	 * group events scheduling is treated as a transaction,
> +	 * add group events as a whole and perform one schedulability test.
> +	 * If test fails, roll back the whole group
> +	 */
> +
> +	/* start group events transaction  */
> +	void (*start_group_trans)	(const struct pmu *pmu);
> +
> +	/* stop group events transaction  */
> +	void (*stop_group_trans)	(const struct pmu *pmu);
> +
> +	/* commit group events transaction */
> +	int (*commit_group_trans)	(const struct pmu *pmu);
>  };


Looks good!

Thanks.