Date: Wed, 15 Apr 2015 09:35:32 +0200
From: Ingo Molnar <mingo@kernel.org>
To: Jason Low <jason.low2@hp.com>
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>
Subject: Re: [PATCH 2/3] sched, timer: Use atomics for thread_group_cputimer
 to improve scalability
Message-ID: <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>
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* 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.

Thanks,

	Ingo
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