linux-kernel - Re: [PATCH 2/3] sched, timer: Use atomics for thread_group

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Date:	Wed, 15 Apr 2015 10:14:12 -0700
From:	Jason Low <jason.low2@...com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Mike Galbraith <umgwanakikbuti@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Mel Gorman <mgorman@...e.de>,
	Steven Rostedt <rostedt@...dmis.org>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	hideaki.kimura@...com, Aswin Chandramouleeswaran <aswin@...com>,
	Scott J Norton <scott.norton@...com>, jason.low2@...com
Subject: Re: [PATCH 2/3] sched, timer: Use atomics for thread_group_cputimer
 to improve scalability

On Wed, 2015-04-15 at 09:35 +0200, Ingo Molnar wrote:
> * Ingo Molnar <mingo@...nel.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

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