Message-ID: <1429118052.7039.99.camel@j-VirtualBox>
Subject: Re: [PATCH 2/3] sched, timer: Use atomics for thread_group_cputimer
 to improve scalability
From: Jason Low <jason.low2@hp.com>
To: Ingo Molnar <mingo@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>, linux-kernel@vger.kernel.org,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Oleg Nesterov <oleg@redhat.com>,
        Mike Galbraith <umgwanakikbuti@gmail.com>,
        Frederic Weisbecker <fweisbec@gmail.com>, Mel Gorman <mgorman@suse.de>,
        Steven Rostedt <rostedt@goodmis.org>,
        Preeti U Murthy <preeti@linux.vnet.ibm.com>, hideaki.kimura@hp.com,
        Aswin Chandramouleeswaran <aswin@hp.com>,
        Scott J Norton <scott.norton@hp.com>, jason.low2@hp.com
Date: Wed, 15 Apr 2015 10:14:12 -0700
In-Reply-To: <20150415073532.GA14091@gmail.com>
References: <1429052986-9420-1-git-send-email-jason.low2@hp.com>
	 <1429052986-9420-3-git-send-email-jason.low2@hp.com>
	 <20150415073340.GB13449@gmail.com> <20150415073532.GA14091@gmail.com>
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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

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