linux-kernel - Re: [PATCH] better align percpu counter (Was Re: [tip:sched/core] sched: cpuacct: Use bigger percpu counter batch values for stats counters

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Message-Id: <20090821125649.7c2e8fa5.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Fri, 21 Aug 2009 12:56:49 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Anton Blanchard <anton@...ba.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	balbir@...ux.vnet.ibm.com,
	Bharata B Rao <bharata@...ux.vnet.ibm.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Ingo Molnar <mingo@...e.hu>, mingo@...hat.com, hpa@...or.com,
	linux-kernel@...r.kernel.org, schwidefsky@...ibm.com,
	balajirrao@...il.com, dhaval@...ux.vnet.ibm.com,
	tglx@...utronix.de, akpm@...ux-foundation.org
Subject: Re: [PATCH] better align percpu counter (Was Re: [tip:sched/core]
 sched: cpuacct: Use bigger percpu counter batch values for stats counters

On Thu, 20 Aug 2009 17:41:23 +0900
KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:

>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> ---
>  include/linux/percpu_counter.h |   12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
> 
> Index: linux-2.6.31-rc6/include/linux/percpu_counter.h
> ===================================================================
> --- linux-2.6.31-rc6.orig/include/linux/percpu_counter.h	2009-08-20 12:09:27.000000000 +0900
> +++ linux-2.6.31-rc6/include/linux/percpu_counter.h	2009-08-20 17:31:13.000000000 +0900
> @@ -14,14 +14,24 @@
>  #include <linux/types.h>
>  
>  #ifdef CONFIG_SMP
> +struct __percpu_counter_padding {
> +	char x[0];
> +} ____cacheline_internodealigned_in_smp;

above alignement is too big...plz ignore this patch :(

-Kame


> +#define CACHELINE_PADDING(name)  struct __percpu_counter_padding name
>  
>  struct percpu_counter {
> +	/*
> +	 * This pointer is persistent and accessed firstly.
> +	 * Then, should not be purged by locking in other cpus.
> +	 */
> +	s32 *counters;
> +	CACHELINE_PADDING(pad);
>  	spinlock_t lock;
>  	s64 count;
>  #ifdef CONFIG_HOTPLUG_CPU
> +	/* rarely accessed field */
>  	struct list_head list;	/* All percpu_counters are on a list */
>  #endif
> -	s32 *counters;
>  };
>  
>  extern int percpu_counter_batch;
> 
> 
> --
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