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

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Message-ID: <20150415073532.GA14091@gmail.com>
Date:	Wed, 15 Apr 2015 09:35:32 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Jason Low <jason.low2@...com>
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>
Subject: Re: [PATCH 2/3] sched, timer: Use atomics for thread_group_cputimer
 to improve scalability


* 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.

Thanks,

	Ingo
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