Re: [PATCH 2/3] sched, timer: Use atomics for thread_group_cputimer to improve scalability

[Jason Low <jason.low2@hp.com>]

On Wed, 2015-04-15 at 09:35 +0200, Ingo Molnar wrote:
> * Ingo Molnar <mingo@kernel.org> wrote:
> 
> > So after your changes we still have a separate:
> > 
> > struct task_cputime {
> >         cputime_t utime;
> >         cputime_t stime;
> >         unsigned long long sum_exec_runtime;
> > };
> > 
> > Which then weirdly overlaps with a different structure on a different 
> > abstraction level:
> > 
> >  struct thread_group_cputimer {
> > 	atomic64_t utime;
> > 	atomic64_t stime;
> > 	atomic64_t sum_exec_runtime;
> >  	int running;
> >  };
> > 
> > So I think it would be more obvious what's going on if we introduced 
> > an atomic task_cputime structure:
> > 
> >  struct task_cputime_atomic {
> > 	atomic64_t utime;
> > 	atomic64_t stime;
> > 	atomic64_t sum_exec_runtime;
> >  };
> > 
> > and put that into 'struct thread_group_cputimer':
> > 
> >  struct thread_group_cputimer {
> > 	struct task_cputime_atomic cputime_atomic;
> >   	int running;
> >  };
> > 
> > Maybe even factor out the main update and reading methods into 
> > expressively named helper inlines?
> 
> Btw., feel free to preserve your original series and turn this 
> factoring out into 1-2 extra patches on top of it: so that we preserve 
> your testing on the original series, and see the structure (and cost) 
> of the factoring out of the new data type.

Okay, I'll add a task_cputime_atomic.

That will convert things like:

    void sample_group_cputimer(struct task_cputime *times,
                               struct thread_group_cputimer *cputimer)

to

    void sample_atomic_cputimes(struct task_cputime *times
                                struct task_cputime_atomic *atomic_cputimes)

which makes more sense, and the new "task_cputime_atomic" can
potentially be used in other places.

Thanks,
Jason